Total Pinealectomy by an Occipital Parasagittal Approach in Sheep Robert J. Dempsey, M.D.,* Jonathan Hopkins, M.D.,* Eric L. Bittman, Ph.D.,t$ and Glenn W. Kindt, M.D.* A reliable method of total pinealectomy in sheep without a resulting significant neurological deficit has been de- veloped and is described. The known effect of light on sheep gonadotropin levels helps validate these studies of its pineal gland. Special attention is given to delineation of the surgical anatomy of the gland and its relationship un- der magnification to the central draining veins of the brain. In this large mammal this relationship differs considerably from that of humans. T]he application of an intrahemi- spheric occipital exposure using magnification, as well as the preoperative administration of steroids and osmotic agents, helped to minimize the effects of retraction and resultant cerebral edema. We have thus been able to in- crease the rate of successful pinealectomy to 83%, al- lowing the development of groups of animals suitable for studies of the neuroendocrine function of the pineal and pituitary glands. DempseyRJ, Hopkins J, BittmanEL, KindtGW: Total pinealectomy by an occipitalparasagittal ap- proach in sheep. SurgNeurol 18:377-380, 1982 The surgical anatomy of the pineal region has been a sub- ject of great interest to neurosurgeons since the early work of Walter Dandy [2]. Clinical experience and detailed studies of cadavers continue to contribute to our under- standing of this region [ 13]. The lack of a good large animal model, however, has made chronic survivor experiments of the effects of pinealectomy difficult. Neuroendocrinologists have found the pineal gland a unique challenge since 1917 when McCord and Allen [11] first proved that extracts of the gland have a biological ac- tion. Lerner and his associates [8] later isolated melatonin as a prospective hormone secreted in a cyclic nocturnal pattern from the gland. Studies of biological rhythms have since suggested that the pineal may mediate the effects of From the *Sectionof Neurosurgery, Departmentof Surgery, "~Michigan Societyof Fellows,ReproductiveEndocrinology Program, and the :~De- partmentsof Pathology and Physiology, The University of Michigan,Ann Arbor, MI. Address reprint requests to Dr. Robert J. Dempsey, Section of Neurosurgery, Universityof MichiganHospital, 1405 E. Ann St., Ann Arbor, MI 48109. Key words: pineal gland; melatonin; pinealectomy;sheep; neuroendo- crinology;pineal tumor. day-length§ on the neuroendocrine system [5, 10, 17]. To allow a systematic study of these effects, a model was de- veloped for pinealectomy in the adult ewe, a long-lived mammal whose seasonal reproductive rhythm is known to be regulated by photoperiodism [6]. Pinealectomy has been described in many laboratory animals [1, 2, 4, 9], including sheep [14]. Unlike that done in small laboratory rodents, whose pineal glands are superficially located, the sheep pineal gland is shielded by the central draining veins of the brain (Fig. 1). Previous attempts to develop a pinealectomy procedure in the ewe have failed to take this venous system into consideration and have resulted in a high frequency of complications (> 45%), often precluding successful pinealectomy [14]. The surgical anatomy of this animal's pineal region pre- sented a challenge because of some marked differences from the human anatomy. An adaptation of the midline occipi- tal approach developed by Poppen for human beings, was utilized in this model [12]. This allowed more flexibility in the exposure necessary for total gland removal in the very confined cranium of the sheep. By delineating the deep venous anatomy of a midline occipital approach to the gland, and by introducing neurosurgical techniques such as microsurgery, complications were reduced to a level accept- able for the production of substantial numbers of pinealec- tomized animals (17%). This allowed for extended studies over many seasons in photoperiodic animals large enough for safe repeated assessments of serum levels of melatonin [15] and the later infusion of the appropriate hormone after removal of the gland. Materials and Methods Mature Suffolk ewes were maintained at the University of Michigan Sheep Research Facility. Each animal was given no food for 24 hours prior to operation. Eighteen hours be- fore operation, ewes were given intramuscular injections of ampicillin (5 mg per kilogram of body weight) and dex- amethasone (0.6 mg/kg). Immediately prior to anesthesia, TurcapsoUL and Emulsifol# were administered orally as car- §The ability of the neuroendocrine system to determine seasons of the year by measuring the lengthof day. thus allowing accurateseasonalreproduc- tive patterns. bISalicylic acid, methyl salicylate,camphor,oil of turpentine, and ginger; Pitman-Moore, Washington Crossing,NJ. #Soybeanoil and polysorbate;Roberts Laboratories,Rockford,IL. 0090-3019/82/110377-04501.25 O 1982 by Little, Brown and Company (Inc.) 377