Benzodiazepine receptors in the rat hippocampal formation: Action of catecholaminergic, serotoninergic and commissural denervation

Abstract The problem of benzodiazepine receptor localization in the rat hippocampal formation has been approached using several methods of selective deafferentation, followed by [ 3 H]flunitrazepam binding studies. The intraventricular injection of 6-hydroxydopamine reduced, after 14 days, the norepinephrine content of the hippocampal formation by 68.4%, and decreased the number of binding sites by 32%, without change in affinity. The intraventricular injection of 5,6 dihydroxytryptamine reduced the serotonin content by 61.5% but did not alter the [ 3 H]flunitrazepam binding. The intraventricular bilateral injection of 0.5μg kainic acid selectively destroyed the pyramidal neurons in area CA 3 of both hippocampi and produced an increase of 28% in [ 3 H]flunitrazepam binding, without change in affinity. These results are discussed in relation to our previous observations about benzodiazepine receptor changes after fimbria-fornix transection. The reduction in [ 3 H]flunitrazepam binding after administration of 6-hydroxydopamine suggests the possible localization of the benzodiazepine receptors on adrenergic presynaptic terminals. The increase in binding sites after destruction of CA 3 pyramidal cells, which are the site of origin of commissural fibers, is tentatively interpreted as resulting from the sprouting of mossy fibers that replace the associational-commissural projections.