Modifications in recognition sites for neurotransmitters in rat hippocampus by kainic acid lesion

The specific binding of the tritiated radioligands of dexetimide, serotonin, clonidine, prazosin, WB-4101 and dihydroalprenolol to hippocampal membranes was determined two weeks after producing a virtual complete degeneration of perikarya by the local application of 0.5 micrograms of kainic acid in the dorsal and ventral parts of the hippocampus. Afferent terminals were unaffected by the neurotoxin since the contents of noradrenaline, serotonin and acetylcholine, as well as the activity of choline acetyltransferase, were not modified. Scatchard analysis revealed that the kainic acid lesion produced a 60% decrease in the density of both cholinergic muscarinic binding sites and serotonin binding sites. A significant portion of alpha 1- and alpha 2-adrenoceptor binding sites are also associated with intrinsic neurons of the hippocampus, as shown by the approximately 30% reduction in the densities of tritiated WB-4101, prazosin and clonidine produced by the action of kainic acid. By contrast, the affinity and density of beta-adrenoceptor binding sites were unaffected by the lesion. It is suggested that the recognition sites of the different receptor populations surviving the lesion most likely reside on homologous and/or heterologous nerve terminals.