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Proc. 6th Symp. Int. Soc. Res. Stereoencephalotomy, Tokyo 1973, part II
Confinia neurol. 37: 120-127 (1975)
Efferent Connections of the Centromedian Nucleus and the
Magnocellular Part of the Medial Geniculate Body in Cats
R. K uroda, H. M urui, K. A kagi, K. K amikawa and H. M ogami
Department of Neurosurgery, Osaka University Medical School, Osaka
With the development of the stereotaxic thalamotomy, it has been
clarified that the therapeutic destruction of the centromedian nucleus
(CM) and the parafascicular nucleus (Pf) are effective for the alleviation
of the intractable pain. M ehler [9] pointed out that the posterior nuclei
group (PO) of the thalamus, including the magnocellular part of the medi­
al geniculate body (MGmc) is a relay of protopathic diffuse pain in the
thalamus, and attached the importance to those rather than the CM and
the intralaminar nuclei. Previously, we have reported that a certain
amount of the secondary trigeminal fibers arising from the nucleus caudalis of the spinal trigeminal nucleus terminated in the ventrobasal and
the intralaminar nuclei of the thalamus in cat [10]. Stewart and K ing
[18] have also described the termination of those fibers in MGmc. Be­
sides the secondary trigeminal tract, the spinothalamic tract, the medial
lemniscal afferent and some of the other afferent fibers have been report­
ed to terminate in MGmc. However, the evidence that the spinothalamic
tract and secondary trigeminal tract terminated in the CM was not ob­
tained in our experiments. The degenerating axons seen in the CM were
only passing fibers. This fact has been recognized by N auta and K uypers
[12] and M ehler et al. [7, 8], The purpose of our report is to clarify the
efferent connections from CM and MGmc in cats anatomically.
Materials and Methods
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Under Nembutal anesthesia and with aseptic precautions, small electrolytic le­
sions were placed stereotaxically on the thalamus and MG in cats. In all animals the
K uroda/M urui /A kagi/K amikawa/M ogami
electrodes were introduced vertically through the ipsilatcral hemisphere according
to the coordinates of Snider and N iemer’s atlas [17J. After survival periods of 7-10
days, the animals were perfused with saline and then lOVo formalin solution under
deep anesthesia. The brains were removed and fixed in formalin for a few months.
Serial coronal sections of 35 iim in thickness were cut on a freezing microtome and
every third of fifth section was stained by Nauta-Gygax method. The lesions were
ascertained by Nissl slain preparations.
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1. MG me Lesions and their Efferent Connections
In three cats (C21, 22, 23) lesions were placed on the MGmc. As con­
trol studies, the lesion on the parvocellular part (MGp) was made in a cat
(C24), and only a needle track was made in another (C25).
Figure 1 shows the distribution of the degenerating axons from the le­
sion in cat C23. The degenerating fibers from the lesion (at B) projected
dorsomedially or medially and cranially. In the case with the lesion
placed out of MGmc, the degenerating fine particles were not observed in
the posterior nucleus, while preterminal degenerations were observed in
the posterior lateral nucleus and the suprageniculate nucleus. As to the in­
terthalamic connections, the MGmc most probably projects fibers to the
nucleus posterior of Snider-Niemer’s atlas which appears to correspond to
the nucleus limitans or its caudal extension of R ioch [15], and others [4,
5]. The suprageniculate nucleus also would probably receive the afferent
fibers from the MGmc.
As to the cortical projections from the MGmc, the anterior ectosylvian
gyrus was noteworthy. In three cases (C21, 22, 23) with an MGmc lesion
the degenerating fibers were abundant in the dorsal part of the anterior
ectosylvian gyrus. A case C24 with lesion in MGp showed a few degener­
ating axons in the anterior part of the anterior ectosylvian gyrus in addi­
tion to the projection to the dorsal part of it (A II). The degenerating
axons in the anterior part of the anterior ectosylvian gyrus were thought
to originate from the unintentional lesion in the ventrobasal nucleus.
In consequence of analysis of the cases the corticopetal fibers from the
MGmc terminated in the anterior ectosylvian gyrus. Most of the relevant
fibers terminated in the dorsal part of the anterior ectosylvian gyrus
which corresponded to the dorsal part of the second somatosensory area
(S II), or the transitional area to the second acoustic area (A II), while
the anterior and middle part of the S II received a small amount of them.
K uroda/M urui /A kagi/K amikawa/M ogami
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Fig. 1. Diagrams of representative levels of the subcortical structure to show the
distributions of degenerating axons (dot) from the lesion (solid black) of the MGmc
in cat C23.
Connections of the Centromedian Nucleus and Medial Geniculate
2. CM Lesions and their Efferent Connections
In four cats (Cl, 2, 5, 6) the lesions were placed in the CM selectively,
and in three cats other thalamic lesions of the CM were made as control.
Figure 2 shows the distribution of the degenerating axons from the le­
sion in cat C5. A small number of fibers passed through the massa inter­
media and terminated in the contralateral CM, Pf, the central lateral nu­
cleus (CL), the paracentral nucleus (Pc) and the ventral posteromedial
nucleus (VPM). In addition, some of them terminated in the midline nu­
cleus on the way to the contralateral side. In the homolateral side, many
fibers terminated in the intralaminar nuclei, CL, Pc, and Pf. The CM had
probably close fiber connections with every ventral nuclei. Some of the
efferent fibers terminated in the ventromedial part of the reticular nucle­
us. The CM projected fibers to the head of the caudate nucleus and the
rostral putamen.
As to the cortical termination, the CM projected some of the corticopetal fibers to the anterior ectosylvian gyrus, the anterior and poterior sig­
moid gyrus, the coronal gyrus and probably the anterior sylvian gyrus.
However, these corticopetal fibers were only sustaining collateral and not
the essential one.
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Various efferent connections to the MGmc have been proved anatomi­
cally and also supported by electrophysiological studies [13, 21, 22]. As
to the efferent connections from the MGmc, many studies were reported,
however, there were some controversies among them. It was because
those conclusions were drawn from the various findings of retrograde de­
generations in the MGmc following cortical excision. Recently, the corti­
cal projection of the degenerating fibers arising from MGmc lesions have
been investigated by NAUTA-Gygax stain. Mehler [9] has insisted on the
efferent projections from the MGmc to the anterior ectosylvian gyrus. As
to the corticothalamic projection from S II, R invic [14], deV ito [3] and
K usama and K awana [6] have agreed with the fiber connection between
the S II and the MGmc.
In our experiments, the efferent fibers from the MGmc to the anterior
ectosylvian gyrus were analyzed and compared to control experiments. As
to the thalamic connections from the MGmc, it was difficult to draw a
conclusion because the needle insersion caused the degenerating axons
K uroda / M u ru i /A kagi /K a m ik a w a /M ogami
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Fig. 2. Diagrams of representative levels to show the distributions of degenerat­
ing axons (dot) from the lesion (solid black) of the CM in cat C5.
Connections of the Centromcdian Nucleus and Medial Geniculate
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which projected to the cortex. At the level of the meso-diencephalic junc­
tion, many degenerating fibers and preterminals were observed in the pulvinar, the pretectal nucleus, the posterior lateral nucleus, the suprageniculate nucleus and the posterior nucleus.
The terminations in the pulvinar and the pretectal area are not yet
clarified, because unintentional small lesions were made in the pulvinar in
addition to the needle tracks in the optic tract.
In our cats with lesions in the MGmc and its adjacent area, a certain
number of terminations were found in the posterior nuclei complex, in­
cluding the suprageniculate nucleus. M orest [11] has also ascertained the
efferent connections from the MGmc to the suprageniculate nucleus by
Golgi stain. Therefore, the MGmc seemed to connect to the posterior nu­
cleus of the Snider and N iemer atlas and the suprageniculate nucleus.
The CM is one of the most effective target points for the alleviation of
pain. However, there are no direct afferent connections in the CM from
the spinothalamic tract and the secondary trigeminal tract. The intrathalamic fiber connections and the cortical projections of the CM efferents
have long been discussed. The degenerating fibers originated from the
CM were distributed diffusely in almost every thalamic nuclei.
Different findings were reported as to the small number of commissur­
al fibers through the massa intermedia and the termination in the ventro­
medial part of the reticular nucleus. C lark and B oggon [2] and W ells
[20] noticed these commissural fibers via the massa intermedia in their
study of the MD lesion, but their origin remained unknown. According to
the Golgi study by Scheibel and Scheibel [16], the CM-Pf complex with
a richly branching system projected to virtually every thalamic field.
These axons spread to the neuropil field of most midline nuclei, medial
nuclei of both sides and to the portions of the ventral lateral nucleus
(VL), the ventral anterior nucleus (VA), the dorsomedial nucleus (MD)
and reticular nucleus. Terminal degenerations were observed in the hom­
olateral MD, CM, Pf, Pc, CL, VPM, VL and VA. These terminal degen­
erations were supposed to be attributed to the CM lesion, but we could
not deduce definite conclusion from our materials.
Concerning the cortical projection of the CM, recently B owsher [[1]
and T otibadze and M oniava [19] reported that the CM projected to the
motorsensory cortex. But these reports also have some limitations owing
to the inevitable lesions, such as the needle track. Therefore, these reports
have involved some controversies. To clarify the cortical projection from
the CM, various approaches to the CM should be attempted.
K uroda/M urui /A kagi/K amikawa/M ogami
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1 Bowsher , D.: Some afferent and efferent connections of the parafascicular-center median complex; in P urpura The thalamus, pp. 99-108 (Columbia
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of the cat (National Research Council of Canada, Ottawa 1960).
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Connections of the Ccntromedian Nucleus and Medial Geniculate
18 Stewart , W. A. and K ing , R. B.: Fiber projections from the nucleus caudalis of
the spinal trigeminal nucleus. J. comp. Neurol. 121: 271-286 (1963).
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nucleus centrum medianum thalamic. J. comp. Neurol. 137: 347-360 (1960).
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Request reprints from: Dr. R. K uroda, Department of Neurosurgery, Osaka Uni­
versity Medical School, Osaka (Japan)
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