Somatostatin-like immunoreactive neurons in the hippocampus: an immunocytochemical study in the rat.

Using antibodies to somatostatin in combination with the avidin-biotin immunohistochemical method, the laminar distribution and morphology of somatostatin-like (SOM-L) immunoreactive cells have been studied in the hippocampal formation of the rat. SOM-L positive cells are present throughout the longitudinal axis of the hippocampus. Most of these neurons are of medium (15-20 micrometers) to large (25-30 micrometers) size with soma of multipolar or fusiform shape. No pyramidal or granule cells contained SOM-L immunoreactivity. SOM-L-positive cells show a preferential distribution in the stratum oriens and stratum pyramidalae of Ammon's horn, and match the description of the polymorphic cells of the hilus area dentata. This geographic segregation may imply a chemical compartmentation of function in the hippocampus.