Rapid Pinealectomy in Hamsters and other Small Rodents ROGER A. HOFFMAN AND RUSSEL J. REITER Physiology Division, Directorate of Medical Research, Edgewood Arsenal, Maryland ABSTRACT Removal of the pineal organ from small rodents may be rapidly accomplished by ( 1 ) immobilizing the skull in a head mounting device and (2) by cutting and removing a circular disc of bone overlying the pineal area with the use of a dental machine and a specially designed circle cutter. Recent investigations in this laboratory have required the use of large numbers of pinealectomized hamsters. Initially, the operation performed with a hand trephine or a dental machine using a n ordinary burr drill was fraught with technical difficulties, excessive bleeding and relatively high mortality. The following procedure using a standard dental machine was developed which permits rapid pinealectomy, minimal bleeding and nearly 100% survival. The hamster skull is small and the skin is so loose that the necessary immobilization of the head to permit drilling is almost impossible. This difficulty was solved by building a base of lucite fitted with ear bars and a n adjustable tooth bar. Essentially this head holder is simply a modification of any standard stereotaxic instrument base. A disc drill was made from stainless steel stock turned down and drilled so as to form a thin walled tube as shown in figure 1. Coarse teeth were filed at one end of a short piece which was attached to the shaft of an ordinary dental drill either by silver solder or by boring and tapping holes in the sides to accommodate 0-80 stainless steel Allen screws. A collar was fitted around the drill, adjusted to the desired depth of cut and tightened with Allen screws. Although figure 1 shows serrations with positive rake when rotating in a clockwise direction, further study has shown that teeth with negative rake are a s good or better; the latter appears to produce less hemorrhage from the diploic vessels. The animals are anesthetized, the bases of the ears are slit vertically to expose the ear canals (not mandatory) and the head of the animal is rigidly mounted i n the ANAT REC., 153: 19-22. holder (fig. 2). The scalp is cut anteroposteriorly along the midline from between the eyes to beyond the base of the skull. The skin flaps are reflected and the underlying fasciae and the insertions of the temporal and occipital muscle masses are scraped free in a n area wider than the diameter of the collar. Careful removal of these tissues from the field is necessary to prevent entanglement with the drill and collar during the subsequent step. At this .0b 2” I ,125’‘ I I I I I I ! I I I Fig. I Diagram of the drill complex. C, collar (outer diameter, 0.353”); DD, dental drill shaft (0.092”); HS, hollow shaft (outer diameter, 0.220”; inner diameter, 0.185”) ; SSAS, stainless steel Allen screw (0-80). 19 20 ROGER A. HOFFMAN AND R U S S E L J. REITER Fig. 2 A photograph of a hamster head mounted i n head holder with bone disc removed. Re-touched sagittal and transverse sinuses are visible. The freed bone disc lies anterior to the opening. point the large venous sinuses of the brain are visible through the skull. The drill is centered on the confluence of the superior sagittal and transverse sinuses. The hole is drilled to the desired depth as set by the adjustable collar. We find that the optimal depth is not quite equal to the thickness of the skull. At this depth, the bone disc is movable but still adherent to the dura. With care, the disc can be removed with little or no bleeding from the underlying vascular channels. Although the pineal gland is not visible, a little practice permits one to remove it by inserting a n open pair of watchmaker’s forceps into the junction of the two sinuses, grasping the stalk and removing gland and stalk in one motion (fig. 3 ) . The white pineal body is about 0.5 mm in diameter (in hamsters) and is unmistakable. Excessive hemorrhage is prevented by rapidly returning the bone disc to its original position and by the application of a cotton pledget with moderate pressure. Bleeding (and possible infection) is further controlled by application of a powdered sulfa compound. The skin flaps are pulled together and stapled. We find that 21 RAPID PINEALECTOMY Fig. 3 Diagram of a mid-sagittal section of a n adult hamster brain showing the relationships of the pineal organ with the surrounding structures and the direction of approach for pinealectomy. CC, corpus callosum; CER, cerebellum; HN, habenular nucleus; IC, inferior colliculus; PC, posterior commissure; SC, superior colliculus; SSS, superior sagittal sinus. a standard desk stapler from which the anterior end of the base has been ground off to the front margin of the stapling plate is rapid and quite satisfactory. Normally, we maintain the animals on oxytetracycline hydrochloride (Cosa-Terramycin, Pfizer) i n the drinking water for the first 2-3 days postoperatively a s a prophylactic measure. Penicillin has been found to have adverse effects on anesthetized hamsters. While other procedures are undoubtedly adequate (see Kitay and Altschule, '54), the use of the head holder and the disc drill permits the operator to pinealectomize an animal in 1-2 minutes. Rats and ground squirrels have been pinealectomized with equal facility by adjusting the collar to change the depth of cut. While the dimensions of the drill and collar as given in figure 1 are those which we have used and found optimal for use on hamsters, they are not critical. The hole size and the collar can be varied to suit other animals. ACKNOWLEDGMENTS The authors are indebted to Mr. Milton Wirth for the construction of the drill complex and stereotaxic instrument base. LITERATURE CITED Kitay, J. I., and M. D. Altschule 1954 The Pineal Gland, Harvard University Press, Cambridge, pp. 8-12.