AUTORADIOGRAPHIC STUDY OF [H-3]FLUNITRAZEPAM BINDING-SITES IN THE SUBNUCLEI OF THE THALAMUS OF RATS RENDERED TOLERANT TO AND DEPENDENT ON PENTOBARBITAL

We examined changes in benzodiazepine binding sites labeled by [H-3]fl unitrazepam in five nuclei of the thalamus, the central medial, centra l lateral, intermediodorsal, ventroposterior, and laterodorsal nuclei, in rats made tolerant to and dependent on pentobarbital. Animals were made tolerant by intracerebroventricular infusion with pentobarbital (300 mu g(10 mu l)(-1) h(-1) for six days) through pre-implanted cannu lae. Pentobarbital dependence was assessed 24 h after abrupt withdrawa l from pentobarbital. Pentobarbital-tolerant rats showed no significan t change in [H-3]flunitrazepam binding sites (B-max and K-d) in any nu cleus examined in the thalamus. In the rats made dependent on pentobar bital, significant increases in the B-max of [H-3]flunitrazepam bindin g without changes in K-d were noted in central medial and central late ral nuclei. GABAerqic (gamma-aminobutyric acid) neurons in the ventrob asal nucleus and in nuclei in the midline group are important in seizu re regulation and arousal. These findings suggest that alterations of benzodiazepine receptors in certain nuclei of thalami are involved in the physiological changes induced by pentobarbital dependence. There w ere no changes in the binding parameters for [H-3]flunitrazepam in pen tobarbital-tolerant rats. (C) 1998 Elsevier Science B.V. All rights re served.