QUANTITATIVE AUTORADIOGRAPHIC STUDIES OF THE EFFECTS OF BILATERAL OLFACTORY BULBECTOMY IN THE RAT-BRAIN - CENTRAL-TYPE AND PERIPHERAL-TYPE BENZODIAZEPINE RECEPTORS

We investigated the discrete regional effects of bilateral olfactory b ulbectomy on central- and peripheral-type benzodiazepine receptors in rat brains at weekly intervals until one month after bulb ablation. Pe rsistent increases in [H-3]flunitrazepam binding to central benzodiaze pine receptors were observed in the cingulum (27%) and in the frontal( 15%) and parietal (14%) cortices. Progressive increases in central ben zodiazepine receptors, reaching statistical significance four weeks af ter olfactory bulbectomy, were observed in the ventromedial thalamic n ucleus (35%), the lateral hypothalamic region (22%), the basolateral a mygdaloid nucleus (23%) and substantia nigra (25%). Persistent major i ncreases (between four- and six-fold) in [H-3]PK-11195 phenyl)-N-methy l-N-(1-methylpropyl)-3-isoquinoline carboxamide binding to peripheral- type benzodiazepine receptors were observed in all anterior olfactory nuclei. Similarly, throughout the time period studied, [H-3]PK-11195 b inding densities were increased two- to three-fold in the piriform cor tex and lateral olfactory tract. These observations confirm the useful ness of [H-3]PK-11195 binding as a marker of neuronal insult in the br ain. Moreover, the persistent regional increases in [H-3]flunitrazepam binding to central-type benzodiazepine receptors suggest that GABAerg ic transmission is altered following olfactory bulb ablation.