Neuroscience Letters, 80 (1987) 39-43 39 Elsevier ScientificPublishers Ireland Ltd. NSL 04799 Benzodiazepine binding increases in the superficial laminae of the trigeminal subnucleus caudalis following central rhizotomy James P. Drew 1,2, Lesnick E. Westrum 1'2, Denis B. Baskin 2,3 and JoAnn E. Franck 1 Departments of 1NeurologicalSurgery and 2BiologicalStructure, University of Washington, Seattle, WA 98195 (U.S.A.) and 3V.A. Medical Center, Division of Endocrinology~Metabolism, Seattle, WA 98108 (U.S.A.) (Received 18 February 1987; Revised version received 4 May 1987; Accepted 7 May 1987) Key words: Benzodiazepine; y-Aminobutyric acid (GABA); Trigeminal; Subnucleus caudalis; Deafferen- tation Benzodiazepine (BZ) binding is being studied in the spinal trigeminal nucleus of the cat 3 and 11 days following unilateral retrogasserian rhizotomy using in vitro autoradiography and computer-assisted densitometry. At 3 days following rhizotomy there is an increase in number and decrease in affinity of flunitrazepam binding sites in the superficial laminae of subnucleus caudalis of the spinal trigeminal com- plex. By 11 days, affinity remains below control values and binding site number shows an insignificant but detectable increase. There is no change in binding site characteristics in deeper laminae at either surviv- al time. The results are discussed in relation to the physiological hyperactivity and synaptic changes which occur following such lesions and to other conditions of deafferentation. Retrogasserian rhizotomy results in distinct patterns of alteration in physiological activity and in fine structural changes at synaptic sites. In the latter, the deafferen- tation causes vacating of specific postsynaptic sites with subsequent reoccupation by terminals with fiat synaptic vesicles. Other studies in normals suggest that this class of terminals may be GABAergic [15]. It is well accepted that a high-affinity modulatory binding site for benzodiazepines (BZ) exists on the GABA receptor-chloride ionophore complex. Thus, BZ is a sui- table marker for this complex. A subset of GABAergic receptors may therefore be localized using the BZ ligand [3H]flunitrazepam ([3H]FNZP) and quantitative in vitro autoradiography [ 12]. In the present study, quantitative autoradiography has been utilized to quantify BZ binding site changes in the spinal trigeminal nucleus of the cat following primary Correspondence: J.P. Drew, Department of Neurological Surgery, RI-20, University of Washington, Seat- tle, WA 98195, U.S.A. 0304-3940/87/$ 03.50 © 1987 Elsevier Scientific Publishers Ireland Ltd.