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Rubro-cerebellar connections an experimental study in the cat.

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AiiatonricaT Institirte, Cniaersity of Oslh, S o ~ t c a y
The existence of fibers passing from the dentate nucleus
via the bracliium conjunctivum to the red nucleus has been
repeatedly demonstrated. As f a r as we have been able to
ascertain, fibers coursing in a n opposite direction, i.e. neurites of cells of the red iiucleus passing to the cerebellum,
have not been generally recognized, although some authors
have advocated their presence (Forel, 1881; Gudden, 1882 ;
Vejas, 1885; Mahaim, 1894; von Monakow, '09). When studping more systematically the sites of origin of cerebellar affereiits from the brain stem i n the cat, one of us (A.B.)
noticed characteristic retrograde (axonal) changes in cells of
the red nucleus following experimental lesions of the cerebellum. Since this finding was made consistently in several animals, the present study was undertaken in a n attempt to
elucidate this pathway more closely.
Altogether 22 experimental animals were employed in this
study. The brains of three normal cats served as control.
Some of the experimental animals have been used also in
other studies of afferent cerebellar coniiections (Brodal, '52,
THE A X A T O X I C A L RECORD. V O L . 118. SO.
MARCH 1934
The modified Gudden method worked out previously (Brodal, '40) was employed. The cats were operated on at the
age of 6-18 days and killed 4-10 days later. Under nembutal
anaesthesia a n d under sterile precautions various lobules and
p a r t s of the cerebellum were removed by means of knife and
suction. The animals were killed by exsaiiguinatioii under a n
overdose of iiembutal or chloroform, the brain and brain
stem immediately dissected free and immersed i n 96% alcohol for fixation. Following adequate fixation the Cerebellum
and the attached brain stem were embedded in paraffin and
sectioned serially a t 15 I-( in the transversal plane. Every 5th
section was niouritecl and stained with Thionine. When it
proved desirable, intervening sections were niountcd and
stained later.
The sections passing tlirough the red nucleus were scarched
for nerve cells presenting retrograde cellular changes. I n
these young animals the cells, the lieurites of which have
been damaged, display clearcut alterations in the course of
a few Hays and will disintegrate completely during the following two to three days. Since a moderate cell loss will be
difficult to detect, it is essential to kill the experimental
animals when the cellular changes are a t their maximum.
This was found to be about 5 days following the cerebellar
ablation. However, on account of the considerable individual
variations in the rates of thc changes (see Brodal, '39, for
particulars), it may happeii that in certain cases the ccllular
changes a r e too slight to be identified, while in other animals
having survived for a similar period most of the altered cells
have already disappeared. The use of a larger number of
aiiiinals enabled us to overcome the difficulties due to these
iiidividual variations.
Before presenting the experimental evidence brief comment
on the normal topography and cellular architecture of the red
nucleus in the cat is appropriate, as is also a short description of the cellular changes in the experimental animals.
I . The normal red .nucleus im the cat
The red nucleus of mammals is generally considered as
composed of a large-celled caudal p a r t and a small-celled rostral part. Descriptions of the red nucleus in the cat have
been given by Hatschek ( '07), von Monakow ( '09), Winkler
and Potter ('14) and by Davenport and Ranson ( '30). Von
Monakow distinguishes altogether 5 subdivisions of the nucleus. Winkler a n d Potter recognize three, while Davenport
and Ranson maintain that it is only possible to distinguish
a caudal compact p a r t and a rostral reticular part. It is clear
from our material that there a r e considerable individual
variations in the architecture of the red nucleus in the cat,
making attempts a t a finer subdivision arbitrary. In view,
furthermore, of the gradual changes in its picture from level
to level, there seems to be little justification for distinguishing separate parts. On the whole our conception of the red
nucleus is in agreement with that advocated by Davenport
and Ranson.
Figure 1 sliows 5 camera lucida drawings of transverse sections through the n~esencephalonof a 15 day old cat. The
drawings a r e taken with equal intervals. The distribution of
cells of different sizes a t these 5 levels is shown to the i.ight.
Camera lucida drawings have been cliecked under the niicroscope, and all cells observed in the particular sections a r e
indicated, their relative sizes being shown appioximately by
the dimensions of the dots. As described hy several previous authors, aniong others by Cajal ('09), three types of
cells, large, medium-sized and small ones may be distinguished
in the red nucleus. Specimens of the different types a r e seen
to the left in the drawing of figure 7, which makes a description superfluous.
When traced from caudal to rostral levels the red nucleus
begins with a rather compact caudal end, made up almost
exclusively of cells of the largest type, with only a few
medium-sized cells intermingled (fig. 8). From this coinpact,
large-celled caudal pole there is a gradual transition in a
rostral direction. There is a decrease in the number of large
cells, which are by and by substituted by medium-sized and
these again by small ones. Even at rostral levels, however,
scattered cells of the large type occui-. Also the average diameter of the cells of each type appears to decrease steadily. Thus
the scattered large cells at rostral levels are distinctly smaller
than their fellows at caudal levels. Concomitant with tliese
changes in cellular composition there is a progressive change
from a compact to a more loose reticular struoture of the nucleus, as will be seen from figure 1. The rostral pole of the
nucleus fuses almost imperceptibly with the reticular formation surrounding it.
I t will be seen from the following description that the distribution of altered cells following cerebellar lesioiis does not
betray any particular topographic subdivision of the nucleus,
nor does the termination of afferent fibers t o the red nucleus,
as far as can be judged from the available literature. There
seems to be little reason, therefore, to distinguish in the cat
more than two chief parts of the nucleus, fusing gradually
Br.c., brachium conjunctivum
Br.p., brachium pontis
C,, lobulus C, of Bolk, pyramis
C?, lobulus C, of Bolk
C'.m., mammillary body
C'.r., restiform bodCr. I and Cr. 11, crus primum and
secundum of ansiform lobule of
C.S., superior colliculas
Flow., flocculus
F.r., fasciculus retroflexus
L., left
L.ant., anterior lobe
L.a.p., anso-paramedian lobule
L.p.m., paramedian lobule
m., nucleus minimus
h-.111,1-1,V I I and V I I I , oculomotor,
nbducent, facial and vestibular
nerve resp.
hT.d., nucleus dentatus
h.f., nucleus fastigii
N.i., nucleus interpositus
N i p . , nucleus interpeduncularis
N.n. 111, nucleus of oculomotor nerve
Km. V, sensory nucleus of trigeminal
N.n. cochl., nuclei of cochlear nerve
h.n. vest., nuclei of vestibular nerve
Nod., nodulas
K.r., red nucleus
Ol.s., superior olive
Ped.c., cerebral peduncle
P.fl., paraflocculus
Po., pons
R., riglit
S.n., substantia nigra
R.r.m., reticular substance of mesencephalon
Uv., uvula
one into the other: a caudal, magno-cellular, rather compact
part and a rostral, parvl-cellular, more reticular part. However, in section 3 of figure l a small lateral extension of tlie
nucleus is seen, forming a fairly well circuinscrilsed group
of rather densely packed small cells. This group which is
clearly to be distinguished in most animals appears t o cor-
Fig. 1 Diagram (made b y means of a projectioll apparatus) showing the
normal topography and cyto-architecture of the red nucleus a s seen in transverse Nissl-stained sections through the mesencephalon of a two week old cat.
The drawings a r e taken with equal intervals. To the right are shown drawings
a t higher magnification of the left nucleus a t the levels represented. The t h e e
types of cells present a r e indicated by dots of different sizes (drawings checked
under the microscope).
respond to the nucleus niinimus of von Nonakow ( '09). However, since our preparations do not reveal changes in this, we
sliall not consider it here.
IT. E x p erinaeizt n 1 r eszi 1ts
( 1 1 ) T h e retrograde cellzilar cliciiiges iiz t k e red iazlclezts f o l lolcing cerebellar Zesioizs. The changes observed in the cells
of the red nucleus following certain cerebellar lesions (vide
infra) a r e of the same type a s those seen in the same experimental animals in other nuclei sending their fibers to the
cerebellum, and which have been described previously ( f o r
example in the external cuneate nucleus, Brodal, '41 : tlie lateral reticular nucleus, Brodal, '43 ; the paramedian reticular
nucleus, Brodal, '53 ; the pontine nuclei, Brodal and Jansen,
'46). Kepresentative specimens of altered cells a r e reprociucecl in figure 7, and in the photomicrographs of figures 912. The chief alteration consists of a tigrolysis, which appears to begin centrally but later affects the> entire cytoplasni,
leaving only a few S i s s l granulrs along the periphery of tlie
cells. The tigrolytic cytoplasm acquires a homogenous, milky
appearance, staining a faint bluish hue in S i s s l preparations.
The nucleus is displaced to the periphery of the cell. I n
normal animals of the sanie agc the nucleus may also be
soniewliat peripherally situated in some cells, but iierer estrciiiely so, wliile in niany of the altered cells the nucleus appears to be 011 the point of being extruded. Sometimes the
nucleus changes its shape, becoming flattened or bean-shaped,
and in niore severely changed specimens the nucleolus map
be diminished and the nuclear nienibrane indistinct. On account of the varying size of tlie cells, it is difficult to decide
whether there is any change in volume, but indications a r e
that there takes place a certain amount of swellinq, with a
rounding off of tlic cell contours.
The time course of the alteratioiis shows considerable variations, but in most animals the clianges a r e fully developed 45 days after the cerebellar lesion has been made. Then the
cells appear to disintegrate rather rapidly, but the later stages
liave not been studied.
The changes described a r e most easily observed in the large
cells of the red nucleus, but they are also clearcut in the
medium-sized ones (see figs. 7 and 10). Conviiicingly altered
cells of the small type may also be seen, but frequently there
may be some doubt whether a particular cell is pathological
or not, since the small amount of cytoplasni makes it difficult
to ascertain moderate degrees of tigrolysis and a possible displacement of the nucleus.
In the experiments to be described below, only cells presenting unequivocal changes of the type described have been
taken into account. This probably means that some cells
being slightly clianged may have been left out of consideration. Even if the alterations registered will thus represent
the minimum of changes and perhaps not the totality, this
procedure was deemed preferable to running the risk of drawing conclusioiis on the basis of possibly equivocal cell changes.
( 6 ) T h e rubro-cerebellar projection. Maximum of cellular
changes in the red nucleus following cerebellar lesions is seen
in animals in which the entire cerebellum has been removed.
The following case is described as a n example.
Cat 0 131. A g e a t operation I 0 days. Killed 8 days later
( F i g s . 2, 9 and 1 0 )
Lesion. By removing part of the occipital bone above the foramen
magnum the posterior part of the verinis and both paramedian lobules
were exposed. Through this opening the entire cerebellum was removed by means of forceps and sucker.
Serial transverse sections show that all what is left of the cerebellum is part of the left flocculus (fig. 2). There is a necrosis extending
into both restiform bodies, both brachia pontis, less into the brachia
conjunctiva, presumably produced by the traction exerted on these
structures during suction. The necrosis is limited to these fiber
bundles and does not exceed their borders. The superficial part of
the vestibular nuclei shows some glial proliferation, otherwise there
are no alterations in the brain stem.
R e d nucleus. Clearcut retrograde cellular changes are found bilaterally (fig. 2 ) . They are most marked in the caudal third of the
nucleus, where more than one-third of all cells are changed. There
is some predominance of affected cells medially. As more rostral
levels are reached, the number of altered cells decreases by and by,
and in the rostral third there are only scattered degenerating cells.
The density of the dots in figure 2 gives a n impression of the relative
number of changed cells a t the levels drawn. The inset in figure 2
shows a camera lucida drawing of the nucleus a t the level of drawing 6. All changed cells are shown by open circles, all normal cells
present by solid dots.
The retrograde changes are especially striking in the large cells
of the nucleus (figs. 9 and lo), but also medium-sized cells are typically altered, showing tigrolysis and a nucleus displaced to the
extreme periphery of the cell. Even some of the small cells are pathological, but the changes in these are less impressive.
The same cellular changes and a similar distribution of altered cells is found in 4 other animals subjected to total
decerebellations (cat 093, age at operation 15 days, killed
5 days later; cat 0 120, age at operation 10 days, killed 5
days later; cat 0 126, age at operation 10 days, killed 6 days
later [fig. 111 ; cat 0 149, age at operation 10 days, killed 9
days later). I n all of these animals only remnants of the flocculi and in two of one paraflocculus were left. I n all of them
there was some necrosis of fiber bundles in the cerebellar
peduncles, and in three of them there was slight superficial
damage t o the vestibular nuclei.
The consistent occurrence of retrograde cellular changes in
the red nuclei in these decerebellated animals permits the
conclusion that some cells of this nucleus send their neurites
to the cerebellum. These cells belong to all types, but a majority of them appears to be of the large type, only few of
the small type, although it is possible that slighter changes
Fig. 2 Diagram of the findings in cat 0 131. Below a section showing the
maximal extent of the lesion. Simple hatchings indicate areas slightly altered,
cross hatchings indicate necrotic areas. Above a series of drawings from equally
spaced transverse Nissl-stained sections of the mesencephalon. The relative
density of dots in the red ni:clei gives an impression of the intciisity of the
changes a t different levels. The inset to drawing 6 is a camera lucida drawing
(checked under the microscope) of the left red nucleus a t this level, showing all
cells present, the normal ones black, those presenting typical retrograde changes
white. See also figures 9 and 10.
in the latter have not been considered significant and have,
therefore, been disregarded. I t follows from the distribution
of altered cells that the rubro-cerebellar fibers take 01-igin
Figure 2
preponderantly from the caudal third of the red nucleus, with
a certain overweight from its medial part. But even a few
cells in the rostral third of the nucleus project on to the
The question may be raised whether the damage to the vestibular nuclei present in most of tlie decerebellated animals
might be responsible for the cellular changes in the red nucleus. However, this daniagc is always superficial and very
moderate, and, therefore, unlikely to give such marked and
widely distributed cellular changes in tlie nucleus. Furthermore similar changes a r c observed in the red nucleus in other
aiiiriials with a n incomplete decercbellation without conconiitant injury to the vestibular nuclei (vide infra). Although
the iiiatc~ialavailalile does not exclude tlic possibility that
tlie vestibular nuclei may receive soiiie rubro-fugal fibers, we
feel safe to conclude from o w esperinieiits that the cerebellum receives tlie neurites of t h e bulk of the changed cells in
the red nucleus.
B’urtliei. information of tlic rubm-cerebellar projection is
obtained from cases wi tli more circumscrihed cercbellar lesions. Iii several aiiinials the cerebellar lesions \ ~ e r cliiiiited
to the verniis. I n some of tliem it incluclecl also tlic fastigial
nucleus. The lesions ill fiof tlicsc cases are shown in figure :
and will be briefly clcscrihed.
(‘at 0 105. (Agv at operation 18 days, Billed 5 days later.) Thc
ri111dal two-thirds of the lobiilns c2 and the rostral half of the lobulns
C I of 1:olli have been reiiiovtd by siiction. There is a small bleeding
in tlie right paranietlian l o b i i l ~ ,hnt n o damage to the ccntral vliite
mattcr ant1 the intra-cerebellar nuclei.
(‘ut 0 12.3. iAgr at opcration 10 days, liilleti 5 days later.) The
cantlal two-thirds of tlic lohiilns c., the entirt. lobnlus cI (pyramis),
11101’~than the left half of tht> lobnlus 1) (uvula) and some of thc
lobului a (nocliilns) have been removetl. Slight damage ha3 been
matlc to tht. niedialmoat part of t h e left paramedian lobule, and the
left fastigiwl nuclrus is almost destroyed. A very small number of
fibws from the most caudal part of the left dentate nuclens may
possibly have h e m cut.
(’(it 0 133. (Age a t operation 9 (lays, killed 5 days later.) P a r t
of thr. lobuliis ~~1 (pyrainis) and almost the entire lobulns b (uvnla)
have been removed. There is a trifling injury to the l e f t fastigial
Cut 0 138. (Age a t operation 8 clays, killed 4 days later.) The
lobulus CI (pyramis) and the caudal third of the lobalus cz have
been removed o r destroyed. The i n j u r y to the latter lobule extends
laterally into the right anso-paramedian lobule and i n the midline
has damaged to a moderate degree both fastigial nuclei.
0 138
0 146
Fig. 3 Diagram showing in outlines on the unfolded cerebellar cortex the extent of the lesions in 6 cats in which chiefly parts of the vermis were removed.
Al~breviationsas in figure 1.
C'at 0 240. (Age a t operation 9 days, lrilled 5 days later.) The
right half of the anterior lobe is almost completely removed. The
lesion extends caudally into the lobuli~sC L ) and has also slightly encroached upon the lobulus c1 ( p y x m i s ) . There is slight affection
of the right fastigial nuclens and the nuclens interpositus but no
affection of the dentate. The right inferior colliculus is superficially
Cat 0 246. (Age a t operation 8 clays, I d l e d 5 days later.) The
middle parts of the lobnlus 4 (culnien) of the anterior lobe have been
removed. A more superficial lcsion extends caudally near the midline
as f a r as to the caudal end of the lobulus c2. There is no damage
to the central white matter and the nuclei.
I n 5 of these cases a s well a s in some others with similar
lesions 110 altered cells could be found in the red nuclei. W e
a r e inclined to conclude, therefore, that the parts of the cerebellum damaged in these animals, namely the anterior lobe,
the middle and posterior parts of the vermis as well as the
nucleus fastigii, do not participate in the rubro-cerebellar
projection. It must be admitted, however, that this possibility
cannot be definitely ruled out, since the absence of retrograde
cellular changes is by itself not conclusive, particularly in
view of the individual variations with regard to the speed
of development of these changes, a s mentioned before. On the
other liaiid, the rather large number of such negative cases
lends support to the conclusion mentioned.
I n one case, cat 0 140 (fig. 3), altogether three typically
changed cells were found in the red nuclei in all sections esamined. Since a moderate involvement of the nucleus interpositus is the only principal difference between the lesion in
this case and the others shown in figure 3, we are iiiclinecl
to assume that a few fibers from the red nucleus terminate in
the nucleus interpositus. This conclusion is supported by the
findings in another case (cat 0 132) illustrated in figure 4.
This shows the lesions in 4 animals in which the cortex of a
cerebellar hemisphere was more or less completely removed.
Cat 0 104. (Age a t operation 18 days, killed 8 days later.) The
right paramedian lobule, the crns I1 of the ansiform lobule and p a r t
of the parafloccnlus have been removed by means of knife and suction.
The sagittal cut made to separate the paramedian lobule from the
vermis has extended a little too f a r rostrally, separating the fastigial
nucleus from the interpositus by a slit. The dentate nucleus is present, but owing to its close vicinity to the lesion of the paraflocculus
there is some glial infiltration in its caudo-lateral pole.
Cat 0 132. (Age a t operation 9 days, killed 5 days later.) Nost
of the rermis, almost the entire right anso-paramedian lobule and
part of the left ansiform lobule have been removed. The right nucleus
fastigii and nucleus interpositus have been removed with o d y slight
glial infiltration in the neighboring parts of the right dentate. On
the left there is partial but rather extensive damage to the nucleus
fastigii and to the nucleus interpositus.
Cut 0 147. (Age a t operation 8 days, killed 5 days later. P a r t s
of tlie left paramedian lobule and of the crus I1 have been removed
with slight encroachment upon the paraflocculus. The left dentate
nucleus is iiitact except for some glial infiltration a n d slighter nerve
cell changps in thp caudalmost p a r t of its lateral pole.
0 104
........ 0 132
++++ R 1 5 2
Fig. 4 Diagram showing in outlines on t h e unfolded cerebellar surface tlie
extent of the lesions in 4 cats in which chiefly parts of tlie cerebellar hemispheres
mere removed. Abbreviations as in figure 1.
Cat R 152. (Age at operation 8 days, killed 5 days later.) Almost the entire left cerebellar hemisphere has been removed, including most of the paraflocculus. Only remnants of the left flocculus
are present. The lateralinost pole of the left dentate nucleus shows
some glial infiltration and some altered nerve cells, but there is no
primary injury to the dentate.
I n three of the cases shown in figure 4 (cats 0 104, 0 147
and R l 5 2 ) no retrograde changed cells were present in the
red nuclei, while in cat 0 1 3 2 a moderate number of such
cells was found (chiefly in the rostra1 p a r t of the caudal third
of the nuclei). Since thus reinoval of extensive p a r t s of the
cortex of the ansoparamedian lobule and of parts of the
paraflocculus is not followed by the occurrence of retrograde
changed cells in the red nucleus, it appears likely that the
rubro-cerebellar fibers do not reach the cerebellar cortex of
the hemispheres. The presence of some altered cells in cat
0 132 is reasonably explained by the extensive removal of
the nuclei interpositi in addition to the cortical removal, a
conclusion in agreement with that drawn from the findings
in the cases shown in figure 3. The findings in another case
(cat 0 129) with removal of almost the entire verniis and
rather extensive damage to the nuclei fastigii and interpositi a r e also in agreement with this. IIowever, the number of altered cells following lesions including the nuclei
interpositi is very moderate as compared with that seen consistently after total decerebellations. The following case provides an explanation of this discrepancy.
('at 0 1 1 9 . Age at o p w n f i o n 8 dayc. Killed 4 days later
(Pigs. 5 and 1 2 )
Lesion. Cy means of a knife a slit was made on the border 1)etween
t h vcrniis and the left hemisphere and the latter removed by suction.
Transverse scrial sections through the cerebellum and brain steni
shorn that the entire left hemisphere, including the parafloccnlus and
floccnlus, has been removed. There is some damage to the lateralmost f o l k of the lobidus 4 of the anterior lobe aiid slight involvement
of thr left side of the lobuliis e2 of the verniis. The left dentate is
cornpletcly removed while there is a imall rernnaiit left of the nnclcns
interpositus. The fastigial nucleiis iq intact. h nrcrosis. presumably
d u e to traction, extends Into thc bmchiiim pontis on the left, hiit
tlicre is no affection of nuclei of the hraiii stein.
IZcd nzcclezu. Typically retrogradc cliangPd cells are found iii both
red nuclei (fig. 1 2 ) . Their. nnnibcr is coiisidcrnbly less than i n the
cascs 11 ith total deccrclbcllations, hut their localization within the
nuclens is the same, i.e. they iirr foiinti chiefly i n its caudal thirtl,
decreasing in number a s more rostral levels are reached. I n the
rostral third scarcely any altered cells are present. The changes are
bilateral, but the numhcr of alterrd cells on the right side, eontralateral to the lesion. is about clonhle of that on the left.
Fig. 5 Diagrammatic representation of the findings in cat 0 119. Above a
series of sections through the mesencephalon slion iiig the distribution and relatim density of retrograde changed cells in the red nuclei after the same principle as in figure 2 . Below drawings showing the esteut of the lesion. The
parts of the cerebellum shown in black in the diagram of the unfolded cerebellar
surf ace hare been totally removed. Hatchings indicate slighter changes. Abbreviations as in figure 1.
The ample occurrence of altered cells in the red nucleus in
this case must be ascribed to the removal of the dentate nucleus, since lesions involving only those parts of the cortex
which have been removed in this case do not produce such
changes.1 The distribution of altered cells within the red nuclei is identical with that following total decerebcllations, but
their number is more restricted, a s might be expected 011 account of the unilateral lesion. Although the method cniployed
does not permit exact quantitative estimates, the changes in
the latter case are so marked that they appear to approach
half of those following decerebellations. The conclusion seems
permissible, therefore, that the bulk of the rubro-cerebellar
fibers terminates in the dentate nucleus. A much smaller
proportion reaches the nucleus interpositus, while no such fibers have been traced to the cerebellar cortex and the fastigial
nuclei. Whether there is any differential distribution within
the dentate nucleus cannot be ascertained. The absence of
changes in the red nucleus when the lateralinost pole of the
dentate is slightly affected (cp. fig. 4) does not exclude that
also this p a r t may receive rubral fibers.
The bilateral occurrence of clianges in the red nuclei in the
last case makes clear that the rubro-cerebellar projection
is crossed as well as uncrossed, and that the proportion of
crossed fibers is considerably larger than that of uncrossed.
The absence of clianges in the red nuclei following removal
of the vermis suggests that the crossing of the rubro-cerebellar
fibers takes place in the brain stern, since fibers crossing in
the cerebellum would have been interrupted in some of these
cases where the lesion extends ventrally to the 4th ventricle.
(c) Szipplemzentary observations. I n an attempt to throw
light on some of the questions raised by the findings reported
above sections were examined from the brains of some cats
suhjected to experiments performed to elucidate primarily
ot he 1- problems .
The limit betnecii the nucleus interpositus and t h e dentate nucleus is not
iiioq~liologicallydistinct. I n the above account the border has been chosen in
agreement with Janseii and Rrodal ('40)' a little more medially than indicated
by Snider ( ' 4 0 ) .
On account of the somewhat diverging views expressed in
the literature concerning the termination of the brachiurn
conjunctivum fibers, silver impregnated frozen transverse seetions through the mesencephalon were prepared from a cat
(B. St. L. 50) i n which the vermis and one cerebellar hemisphere had been removed 5 days before sacrifice, with the aim
of establishing more precisely the termination than can possibly be clone by the Marchi method employed by previous
workers. I n these sections the massively degeneraled brachiuni conjunctivum could be easily followed through its decussation and into the contralateral red nucleus. Terminal,
very fine degenerating fibers were abundant in the caudal part
of the nucleus, and some degenerating terminal boutons were
also seen. I n the caudal third the majority of fine fibers in
the nucleus were degenerating, only few fine fibers appearing normal (fig. 13). Degeneration was somewhat more
marked ventro-medially than laterally. As more rostral levels were reached the number of degenerating terminal fibers
showed a steady decrease, but even a t a level corresponding
to drawing 2 of figure 1, there was still a considerable number of fine fibers in degeneration, also here more conspicuous
medially (fig. 14).
While a single case like this does not give information of
details it permits the conclusion that the termination of
brachiurn conjunctivum fibers is not limited to the caudal
p a r t of the nucleus, even if it is more abundant here than a t
rostral levels. There appears to be a similar distribution of
termination of the afferent cerebellar fibers as of the cells
of the red nucleus projecting on to the cerebellum. It was,
however, not possible to detect in these silver preparations
cells which could be identified as being in the state of retrograde degeneration (presumably because the animal was adult
and had survived for 5 days only). The interesting question,
whether the cerebello-rubral fibers establish synaptical contact with cells which project back to the cerebellum could,
therefore, not be answered.
Since the rubro-spinal tract is known to take origin from
the caudal p a r t of the red nucleus, it was of interest to compare the distribution of retrograde cells following decerebellations with the distribution following interruption of the
rubro-spinal tract. Two cats (0 141 and 0 144) in which transverse lesions had been made in the spinal cord a t the level
o f C, at the age of 11 days and which had been sacrificed 5
Fig. 6 Diagram showing the numbers of retrograde changed (hatchings) and
normal (white) cells in three caudal sections from the red nucleus in a decerebellatcd cat (0 131) and in a cat in which the rnbro-spinal tract had been
transected a t the level of C, (0 141). Column I represents the most caudal
of the sections of the series passing through the red nucleus; between sections
I and I1 and I11 there is a n interval of 4 sections which mere not mounted.
Since the first section cuts the nucleus more caudally in cat 0 141 than in 0 131
cell numbers a r e less i n all sections from this animal than in 0 131. Cp. text.
days later, were uscd f o r this purpose. AIicroscopical examination showed that in both of them the lateral funiculus
had been completely transected. The retrograde changes in
the contralateral red nucleus involved large, mediuni-sized
and sniall cells and were most abundant in the caudal third,
decreasing by and by in a rostra1 direction. The altered cells
were, therefore, found a t the same levels of the nucleus as
the changes following decerebellation, but there was a tendency for the affected cells to he located laterally.
On account of the similar distribution of the cells giving
origin t o cerebellar and spinal fibers, and in view of the
statement by Cajal ('09, vol. I, p. 255) that some cells of
the red nucleus have neurites which dichotomize close to the
perikaryon, the possibility must be considered that the same
cells may project to the cerebellum and to the spinal cord.
The normal and retrograde changed cells in one case of spinal cord lesion (cat 0 141) and in one case of decerebellatioii
(cat 0 1 3 1 ) were, therefore, counted in the three most caudal sections of each series (after having been drawn in a
projection apparatus and controlled under the microscope).
Only cells representing the fully developed picture of retrograde changes were considered as significant, all other cells
were counted as normal ones. Tangentially cut cells without
a nucleus were discarded.
The diagram of figure 6 shows the numbers of typical retrograde cells (hatchings) and of normal cells (white) in the
three sections from the two cases, column I representing the
most caudal section. As will be seen, in the decerebellated
animal (0 131) in the two caudalmost sections more than half
of the cells a r e altered, in the spinal animal this is the case
only a t level IT. I n sections rostral to those represented the
proportion of altered cells decreases by and by in both cases.
(The inset in fig. 2 is from the section following rostral to
section 111here.) When the three levels considered a r e taken
together, they contain in the decerebellated animal 179 cells,
95 of which a r e altered, i.e. 53% of the cells present retrograde changes. I n the animal with transection of the rnbrospinal tract at Cs, there a r e altogether in the three sections
130 cells, 61 of which a r e pathological, i.e. 47%. These findings will be discussed below.
The changed cells of the red nucleus described and illustrated in this paper present all those features which are considered a s evidence of retrograde cellular alterations, i.e.
changes occurring in the perikarya of nerve cells following
transection of their neurites. Even if such changes, as f a r as
we a r e aware, have not been observed in the red nucleus following lesions of the cerebellum by previous authors we feel
convinced that their presence in the experimental animals betrays the existence of true rubro-cerebellar fibers, terminating
chiefly in the dentate, to a small extent also in the nucleus
iiiterpositus. This interpretation is supported by the very
close similarity between the celllular changes described and
those observed in other nuclei, the cerebellar projection of
which has been substantiated also by other methods. Furtliermore, exactly similar changes occur in the cells of the red nucleus following lesions of the brain stem or upper p a r t of
the cervical cord involving the rubro-spinal tract, as we have
been able to verify ourselves.
I t should be emphasized, however, that the lack of retrograde changes in a nucleus does not warrant the conclusion
that it does not contribute fibers to a particular fiber bundle
which has been transected. Our experiments, therefore, indicate the minimum of possibly existing connections, the more
so since only definitely altered cells, presenting a clearcut
picture of retrograde changes, have been taken into account.
We a r e not entitled to exclude definitely that a few of the
rubro-cerebellar fibers may terminate in the fastigial nucleus
or in the cerebellar cortex, even if the consistently negative
findings in a fairly large number of cases make this unlikely.
I n spite of the limitations inherent in the method employed
here, it is nevertheless the best suited at present. Since the
rubro-cerebellar connections a r e crossed as well as uncrossed,
a study of the later stages presenting cell loss would be less
satisfactory on account of the lack of a normal control side.
I t is of some interest to compare our findings with obsei-vations reported by some early authors who have advocated the presence of rubro-cerebellar connections. Fore1 in
1851 was the first to describe a n atrophy of the posterior third
of the red nucleus in a rabbit in which he had damaged the
brachium conjunctivum and Gudden (1882) and Vejas (1885)
observed the same following extirpation of one cerebellar
hemisphere. Mahaim (1894) following transection of the superior cerebellar peduncle in a one day old rabbit found 4;
months later an almost complete disappearance of nerve cells
in the caudal third of the contralateral red nucleus, and a
smaller loss of cells in its middle third. Some of the cells in
the altered parts of the nucleus were diminished in size. All
these early authors employed the original Guddeii method,
operating their animals immediately after birth or in the
course of the first day and kept them for several weeks or
The findings made by these authors were not considered
valid by subsequent workers, and the objections were made
that there were accidental lesions, or e.g. by Cajal, that the
changes were transneuronal. The observations made in the
present study leave no doubt, however, that these authors were
right in concluding that fibers from the posterior third of
the red nucleus pass to the cerebellum, even if their assumption that the brachiurn conjunctivum is composed of descending fibers only has been disproved.
The distribution of retrograde changed cells in the red nucleus observed i n the present investigation is practically identical with the sites of cell loss reported by Mahaim (1894) in
his careful study. However, the smaller homolateral contribution of rubro-cerebellar fibers demonstrated here has
been overlooked by the early authors, since they examined
their animals after a lapse of time when all altered cells had
disappeared. It is in agreement with our findings that Maliaim did not find alterations in the nucleus minimus.
A comparison between the rubro-cerebellar projection as
determined here and the cerebello-rubral connections studied
by numerous previous authors is of some interest. On most
points these two fiber systems betray striking similaritim2
21t has been assumed here t h a t the rubro-cerebellar fibers enter the cerebellum yia. the brachiurn eonjunctivum. Our experiments, however, do not permit
us t o state this with certaintr, and me are not entitled t o exclude t h a t the films
may enter via the restiforin bodr or the bracliiuni pontis, although this appears
less likely.
Almost all authors a r e i n agreement with regard to the
complete crossing of the fibers of the brachium conjnnctivum
(for example Klinioff, 1899 ; Allen, '24 ; Mussen, '27 ; Gerebtzoff, '36). Probst ('02), however, has suggested that there
niay be also some uncrossed fibers to the red nucleus, but he
derives them from the fastigial nucleus. With regard to the
crossing of fibers, there may, therefore, be a difference between the rubro-cerebellar and the ccrebello-rubral projections. It is possible, however, that a minor homolateral
contingent of cerebello-rubral fibers has been disregarded by
the workers who have employed the I\Iarchi method. Our
case of hemidecerebellation is suggestive of terminal degeneration also in the homolateral nucleus.
While all authors agree that the dentate nucleus is an iniportant source of the fibers of the brachium conjunctivum,
others have adduced evidence that fibers from the nucleus
interpositus, corresponding to the globose and emboliform
nuclei in man, also take p a r t in the projection (Klirnoff, 1899;
-411ei1, '24 ; Mussen, '27 ; T i n k l e r , '27 ; Gerebtzoff, '36 ; J a n sen and Janseii). Some even niaintaiii that a small contribution comes from the fastigial nucleus (I'robst, '02 ; Preisig,
'04). l y e have not been able to deirionstrate rubro-fastigial
fibers (although their presence cannot be excluded), but our
study makcs clear that the bulk of the rubro-cerebellar fibers reach the dentate while a small proportion terminates
in the nucleus interpositus. A p a r t from the more moderate
number of fibers related to the nucleus interpositus in the
rubro-cerebellar than in the cerebello-rubral projection there
appears thus to be a correspondence between these fiber systems with regard to their relation to the intra-cerebellar nuclei. Of relevance in this connection a r e Hassler's ('50) findings in human material. According to Hassler the brachium
coiijunctivum fibers originating in the nucleus emboliformis
reach the central nucleus of the thalamus (centre m6dian of
Luys), the fibers from the parvi-cellular p a r t of the dentate
pass to the ventral thalamic nucleus, while only those from
tlic niagno-cellular, phylogenetically oldest p a r t of the dentate
tcrniinate in the red nucleus, in its caudal magno-cellular
(which is small in man) as well as in its parvi-cellular part.
Authors working experimentally who have considered this
problem, have expressed the opinion that the fibers from the
nucleus interpositus and those from the dentate reach the
same p a r t s of the red nucleus (Allen, '24; I\lussen, '27). It
should be recalled, however, that the Itlarclii nicthod, cniploycd by these authors, is not well suited to cleterniine the
exact termination of degenerating fibers, and the fibers from
the nucleus interpositus niay chiefly be fibers passing by. The
study of cell loss in Hassler's cases makes possible more definite conclusions. It would, therefore, not be impi*obable that
conditions also in the cat a r e in principle as Hasslcr has described them in man. If so, the parallclism between the
(webello-rubral and rubro-cerebellar projections would be
very close with regard to their relation to tlie i1iti.a-cerebellar
nuclei. However, it appears from tlie studies of Janscn and
Jansen, Jr. (in press) that although the projections of the dentate and the nucleus interpositus a r c not identical, the conditions in tlie cat appear not to be as described for inaii by Hassler ('50). Phylogenetical differences will, of course, have to
be taken into account when this problem is to be studied.
The rubro-cerebellar fibers, as has been seen, take origin
chiefly from the caudal, magno-cellular p a r t of the red nucleus, but scattered fibers come also from the rostra1 parvicellular part. This area of origin c o i n d e s with that to
which most authors have traced cerebello-fugal brachium
conjunctivum fibers, be they all derived from the dentate o r
some also from the nucleus interpositus. The distribution of
terminal degeneration within tlie red nucleus following removal of one-half of the cerebellum confirms this parallelism.
A two-way connection between the dentate and the red nucleus, therefore, exists, and it appears likely that a considerable nunibcr of cells in the caudal p a r t of the red nucleus
which project o n to the dentate mag be influenced by impulses from this nucleus. Whether the cerebello-rubral fibers
establish spnaptical contact with the perikarya of the rubroccrebcllar fibers, we have, however, not been able t o decide.
A final question to be considered is the relationship between
the rubro-spinal and the rubro-cerebellar projections. The
rubro-spinal tract has been shown to take origin chiefly from
the caudal niagno-cellular p a r t of the red nucleus ( e g . by
Preisig, '04; von Monakow, '09; and others), and our series
with spinal cord lesions confirm this. They also show that
some fibers come from the parvi-cellular part, in decreasing
numbers as more rostra1 levels a r e reached, and that not only
large cells but also medium-sized and small cells give origin
to some rubro-spinal fibers as mentioned by von h4onakow
( '09). The rubro-spinal and the rubro-cerebellar projections,
therefore, appear t o be derived from the same areas of the
red nucleus, a p a r t from a slight difference insofar as the
cerebellar fibers take origin with a certain preponderance from
the medio-ventral parts, the spinal fibers more from the lateral p a r t of the red nucleus. Since the number of altered
cells in the red nucleus following decerebellations as well
as following high level spinal cord lesions is remarkably
large, the possibility suggests itself that some of the cells
may give origin, by r~ieaiisof a branching neurite, to both
types of fibers, a possibility supported by Cajal's Golgi studies. The results of quantitative studies performed to test
this possibility a r e represented in the diagram of figure 6.
Fifty-three per cent of the cells in the caudal part of tlie
red nucleus show changes following decerebellation, 47 5 a r e
changed following a lesion at C, of the spinal cord. Even
if thus these figures togetlier account for all cells in the caudal p a r t of the nucleus, the values obtained a r e certainly too
low. First, only cells showing fully developed retrograde alterations have been taken into account, and i t is almost certain that in both cases some cells with slighter clianges, representing earlier phases of their development, h a r e been
disregarded. Second, a transection of the rubro-spinal tract a t
tlie level of C, can scarcely be imagined to l i a w cut all rubrospinal fibers and will at least have spared possible rnbrobulbar fibers (von Monakow, '09).
The fiiidiiigs, therefore, strongly suggest that sonie cells of
tlie red iiuclcus project by means of a braiichirig ncnrite to
the dciitate riuclcus as wcll as to the spinal cord." It is of interest in tliis corincctioii to recall that sonic of the cerebcllorubral fibers projcct caudally by means of a collateral, forming the brachium coiijuiictivum desceiiclens. Even if it is as
yet uiikiiowri to what extciit the terminations of tlicse two
descciidiiig pathways may be icleiitical, tlieir cxistcncc furnislies anotlicr cxample of the parallelism in the organization
of the cerehello-rubral and rubro-cercbcllar connections.
Tlie iuiictioiial sigliificarice of the pathway dciiionstrated
in this study remains a subject f o r pliysiological studies. IVe
sliall refrain from such speculations wliicli may be made at
our present state of knowledge. Suffice it to d r a w attentioii
to tlie fact that this ccrcbcllo-rubro-ccrebellar patliway is anotlier example of systems made up of fibcw conducting in
botli directions, organized so as to rriake possible iicrvous
activity in closed neuroiial circuits and rcpresciiting tlic structural basis of fcetl-back mcclianisms. Two-way coiiiiectioiis
of this type appear, iiideed, to bc 11ioi*c1common tliaii hitlicrto
The existelice of rubro-cci*cbcllsr connections, advocatcd by
sonic carly authors, litis not been generally admitted by subscqueiit investigators. By tlic use of the modified Gudclen
method it lias becii possiblc to dcmonstra tc tlicsc conncctions.
A n account of the iio~.rrialarc1iitectui.e aiicl topography of
tlie red nucleus in the cat is given. Tliew seems to be no
" If t h e assumption set forth licre is cotreet, it m:iy seem strange t h a t these
cells renct equally well x i t h retiogr:tde clinngcs to :I transection of either of
tlieir two neuritic branches, since tlir pwserration of proximal eollaterals lins
1)een fwqiimtly adduced t o explain n lack of retrogindc c1i:rnges in t i e n e cells
following traitsection of tlieir neuritcs. IIowever, this protecting influence of
piesrrred coll:itcr:ils, :is far a s TIC :ire awaie, has never been pro\ed. On the
other Ii:ind i t is well Itno\v~.nthat different ncivc cells exhibit marked diffcrriices
with rcgnrd to thcir tcwctio~l to :I tiansertion of their nenrites.
reason to distinguish other subdivisions than a caudal niagnocellular aiid a rostra1 parvi-cellular part, fusing without sliarp
tisaiisitions. Even in tlie caudal p a r t there a r c sonic siiiall
cells, and scattered large cells occur in the rosti-a1 part.
Following total decerebellations in 6 cats aged 8-3s clay,i
and killcd 5-9 days later typical retrograde cliaiigcd cells occur in the red nucleus. All types of cells are affected, most
of them being found in tlie caudal pole, where niore tlian lialf
tlie iiuniber of cells present arc afiected, hut also in the rostral p a r t of tlie nucleus scattered altered cells occur. It is
concluded that tliese cells send their neuiaites to the cerebcllurn.
Following lesions restricted to the cerebellar vermis aiid
tlie nucleus fastigii or to the cortex of tlie hemispheres 110
changes a r e found in tlie red nucleus. Wlieii the iiucleus
interpositus is damaged there are a few altered cells, and
when the dentate iiucleus is included in the lesion tlicrc is
a n affection of about half as niaiiy cells as wheii the cntirc
cerebellum is removed. Considerably niore cells are affected
in the contralateral nucleus than in tlie lioniolatcral. It is coileluded that the rubro-cerebellar projection is chiefly crossed,
to a less extent uncrossed, and tliat the hulk of its fibers iwicli
the dentate nucleus, a small contingent the nucleus iiiterpositus.
The distribution of the cells of origin of the rul~ro-cerebc~ll~i1~
projection coincides very closely with the terminal area of tlic
cerebello-rubral fibers a s determined by the method of terniinal degeneration. The rubro-spinal tract also takes origin
from the same p a r t of the nucleus. Quaiititative cstiiiiatcs
niake probahlc that tliere ai'e in the caudal p a r t of the retl
iiucleus a certain number of cells which by nictiiis of n dicliotomiziiig iieurite projects o n to the cerebellulll a s well a s to
tlic spinal cord. The rubro-cerebellar and tlie cerebello-rul)ral
fibers establish a two-way coniicction between the clelitatc 1111cleus aiiti the red nucleus.
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C:inier;i lucicia drawings of Sissl-st:iined krrgc, medium-sized a n d sm:ill cells
froin the normal red nucleus in cats two t o tliiee weeks old ( t o tlie left) and
of the same types of cells in the fully developed stage of retrograde changes
folloiring deeerebellntioii (to the right). X GOO.
Pliotonrierogr:~pli froin the cauc1:rl p:rrt of the red nnclcus in a norn1:11 eat,
1.8 (1:iys old. Chiefly largc, l)iit, nlso ~nedi~inr-sized
and small cells :ire picsent.
x 260.
Pliotoniierograph froin the ca:rud:il p:ti,t of tlic red nucleus in c a t (0 131 j ,
deecwl)cllxted 10 days old, killed 8 d:iys 1:itrr. Numerous cells present t y p r:il ictrogr:idc eliangrs. X 65.
10 Pliotoiiiicrogrnph from tlrc red nuc1r:ns a s sliowir i n figiiw 9. Most crlls prcsciit are patlio1ogic:il. X 260.
11 Photomicrograph f roni the cnndal p a r t of the red nuclciis ill annt1ic.r w t .
(0 12C;), dccerebel1:itcd 10 days old, killed G (lays Inter. X 260.
12 Pliotoniicrograpli slio\ring retrograde changed cells in the caudal p a r t of tlic
riglit rrcl nucleus iii c a t 0 119, following reiiiov:il of the l e f t ce1~1~ell:ir
hciuisplicre and dentate niiclcns. The anini:rl mas operntrd on 8 d a y s old :mcl
killed 4 days later. X 260.
1:3 and 14 P1iotomicrogr:iplis of silrcv imprcgiiatrcl t,r:insvcrsc sections (Glees ’
nictliod) froin the red nricleiis of :in :idult rat, killcd 5 d ay s a f t e r a n estirpntion of tlic contr:ilatcwl ceiebell:rr hnnisplicre. More nbuncktnt 1)r(ltcriiiiiinl and terminal degenerating fibers (some of them iiidic:itcd l y a r rows) iii tlic c:ind:il part of tlir nnclcns ( 1 3 ) tlraii in tlrc rostxil p a r t ( 1 4 ) .
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