Neuropeptide Y-containing interneurons in the hippocampus receive synaptic input from median raphe and GABAergic...

Neuropeptide Y has been extensively studied in the central nervous system due to a possible involvement of neuropeptide Y-containing neurons in cognitive functions. In the hippocampus neuropeptide Y is present in a subpopulation of nonpyramidal cells, which control the firing of hippocampal output neurons. In the present study we examined whether septohippocampal and raphe-hippocampal afferents--known to have a powerful effect on hippocampal electrical activity patterns--innervate neuropeptide Y-containing neurons in the hippocampal formation of the rat. Using a combination of pre- and postembedding immunostaining and tracing with Phaseolus vulgaris leucoagglutinin (PHAL) we showed that GABAergic afferents arising from the medial septal area extensively innervate neuropeptide Y-containing neurons. Afferents of median raphe origin, most of which are thought to be serotonergic, were also found to make multiple synaptic contacts with these cells. Thus, the neuropeptide Y-containing subpopulation of interneurons--which innervate distal dendrites of principal cells--are also among those through which different subcortical nuclei modulate information processing in the hippocampal formation.