Evidence for a cyclic GMP mechanism in the mediation of hippocampal post-tetanic potentiation.

Correlative electrophysiological and biochemical techniques were used to study hippocampal post-tetanic potentiation in acutely prepared rabbits following stimulation of the medial septal region and contralateral hippocampal field CA3. The results indicate that calcium ions, guanosine-3':5'-monophosphate, and phosphodiesterase inhibitors selectively enhanced the duration of post-tetanic potentiation. Potassium ions selectively enhanced tetanic potentiation. Adenosine-3':5'-cyclic monophosphate suppressed both tetanic and post-tetanic potentiation. The electrophysiological findings were supported by biochemical observations that guanosine-3':5'-monophosphate levels show marked increases following tetanic stimulation of either the medial septal region or contralateral hippocampal field CA3 pathways. The data suggest that a calcium-dependent process in the presence of a guanosine-3':5'-monophosphate mechanism promotes periods of hippocampal pyramidal cell hyperexcitability. The mechanism by which the cyclic nucleotide alters potentiation does not appear to be coupled to a single receptor variety.