Characterization of Neurotransmitter Receptors in the Rat Hippocampal Formation

The hippocampal formation has been extensively research in terms of its putative neurotransmitters, anatomical connections, and behavioral relevance. An aspect of importance is the assessment of apparent neurotransmitter receptors by using receptor binding assays. In the present study, such assays were done in vitro to investigate alpha 1-adrenergic, alpha 2-adrenergic, beta-adrenergic, muscarinic cholinergic, benzodiazepine, and opiate receptors in the rat hippocampal formation. The corresponding radioligands for these receptors were 3H]prazosin, 3H]p-aminoclonidine, 3H]dihydroalprenolol, 3H]quinuclidinyl benzilate, 3H]flunitrazepam, and 3H]naloxone. An analysis of the binding parameters for the ligands indicated saturable binding of a high affinity and the following rank order of maximal binding capacities: 3H]flunitrazepam greater than 3H]quinuclidinyl benzilate greater than 3H]naloxone greater than 3H]p-aminoclonidine greater than 3H]prazosin greater than 3H]dihydroalprenolol. Competition experiments with pharmacologic agonists and antagonists confirmed the specificity of each ligand. The results are integrated with information on other types of receptors and with neurotransmitter concentrations, and discussed in terms of hippocampal function.