Differential regulation of 'central' and 'peripheral' benzodiazepine binding sites in the rat olfactory bulb

The density of [³H]flunitrazepam and [³H]Ro 5-4864 binding sites was examined 19-21 and 27-31 days after surgical isolation of the olfactory bulbs. While statistically significant reductions in [³H]flunitrazepam binding were observed in the olfactory bulbs at both intervals, a significant reduction in [³H]Ro 5-4864 binding was observed only at 27-31 days after surgery. No consistent changes in the binding of either radioligand were observed in cerebella. Extirpation of the olfactory bulbs resulted in a significant reduction in the convulsant potency (but not efficacy) of Ro 5-4864, while neither the potency nor efficacy of pentylenetetrazole was affected by this procedure. These results suggest that benzodiazepine receptors and 'peripheral-type' binding sites for benzodiazepines are regulated independently, and that at least a subpopulation of peripheral-type binding sites are associated with neuronal elements in the olfactory bulb. These data also suggest that peripheral-type binding sites for benzodiazepines in the olfactory bulbs may influence the convulsant actions of Ro 5-4864.