Cholinergic innervation of mossy cells in the rat fascia dentata

Hilar mossy cells are the main cells of origin of the commissural/associati onal projection to the inner molecular layer of the rat fascia dentata. In order to analyze the cholinergic innervation of hilar mossy cells, a light and electron microscopic double-labeling technique was used. Immunolabeling for calcitonin gene-related peptide (CGRP) was employed to identify mossy cells and immunocytochemistry for choline acetyltransferase (ChAT) was used to label cholinergic septohippocampal fibers. Cholinergic boutons were abu ndant around mossy cell somata and on their proximal dendrites. Electron mi croscopy confirmed that many of these boutons formed synapses with the CGRP -positive mossy cells. These data demonstrate a direct innervation of hilar mossy cells by cholinergic septohippocampal afferents. This connectivity c ould contribute to the electrophysiological behavior of mossy cells during theta oscillations. (C) 1999 Wiley-Liss, Inc.