SOMATOSTATIN-CONTAINING NEURONS IN RAT ORGANOTYPIC HIPPOCAMPAL SLICE CULTURES - LIGHT AND ELECTRON-MICROSCOPIC IMMUNOCYTOCHEMISTRY

Light and electron microscopic immunocytochemical techniques were used to study the interneuron population staining for somatostatin (SRIF) in cultured slices of rat hippocampus. The SRIF immunoreactive somata were most dense in stratum oriens of areas CA1 and CA3, and in the den tate hilus. Somatostatin immunoreactive cells in areas CA1 and CA3 wer e characteristically fusiform in shape, with dendrites that extended b oth parallel to and into the alveus. The axonal plexus in areas CA1 an d CA3 was most dense in stratum lacunosum-moleculare and in stratum py ramidale. Electron microscopic analysis of this area revealed that the largest number of symmetric synaptic contacts from SRIF immunoreactiv e axons were onto pyramidal cell somata and onto dendrites in stratum lacunosum-moleculare. In the dentate gyrus, SRIF somata and dendrites were localized in the hilus. Hilar SRIF immunoreactive neurons were fu siform in shape and similar in size to those seen in CA1 and CA3. Axon collaterals coursed throughout the hilus, projected between the granu le cells and into the outer molecular layer. The highest number of SRI F synaptic contacts in the dentate gyrus were seen on granule cell den drites in the outer molecular layer. Synaptic contacts were also obser ved on hilar neurons and granule cell somata. SRIF synaptic profiles w ere seen on somata and dendrites of interneurons in all regions. The m orphology and synaptic connectivity of SRIF neurons in hippocampal sli ce cultures appeared generally similar to intact hippocampus. (C) 1994 Wiley-Liss, Inc.