Somatostatin neurons and their projections in dog diencephalon.

Immunocytochemical localization of the tetradecapeptide somatostatin was performed in dog brain using the unlabeled antibody enzyme method. A large population of immunoreactive neurons was seen in the periventricular areas of the preoptic area and anterior hypothalamus. This field of neurons extended into the paraventricular nucleus, arcuate nucleus and tuberal areas surrounding the ventromedial nuclei. Fibers from the periventricular somatostatin cells projected into the median eminence, the third ventricle, the pars nervosa of the hypophysis, the organum vasculosum of the lamina terminalis, the medial preoptic area and the interstitial nucleus of the stria terminalis. The tuberal cells projected to the ventromedial nucleus and the cells of the arcuate nucleus terminated within the arcuate nucleus as well as within the contact zone of the median eminence. These findings suggest that somatostatin can exert hormonal effects via the vasculature or the cerebrospinal fluid, or transmitter and/or neuromodulatory effects via contacts with other neurons.