Ontogeny of somatostatin-containing neuron system of the rat cerebellum including its fiber connections: an experimental and immunohistochemical analysis.

Ontogeny of somatostatin (SRIF) neuron system of the rat cerebellum was investigated by means of the indirect immunofluorescent method. In addition, several operations were performed to provide the evidence of understanding the cerebellar SRIF innervation. SRIF-positive structures appeared in the primordium of the cerebellum of the fetus at gestational day 16 (14-15 mm embryos). From that time on, SRIF-positive structures identified in the cerebellum increased in number and the greatest number of SRIF-positive structures were detected in the cerebellum of the rat between newborn and 7-day-olds. Afterwards, these structures decreased remarkably in number and only a few if any SRIF-positive structures were observed in the cerebellum of the adult rats. These facts might suggest that SRIF might perform some important roles in the development of the cerebellum. The present study further elucidated that cerebellar SRIF was supplied by at least two types of sources; one was situated within the cerebellum and the other in the extracerebellar regions. The former one innervates mainly the vermis and partly the hemisphere, while the latter one projects mainly to the hemisphere and partly to the vermis.