Innervation of the teleost pituitary

Abstract

This review covers the available data on the types of nerve fibers which innervate the teleost pituitary. Two types of nerve fibers (type “A” and “B” according to Knowles) innervate the glandular cells of the adenohypophysis, type “A” more related to MSH-secreting cells, and type “B” concerned with all cell types. While type “A” seems to orginate from the preoptic nucleus (NPO), evidence is presented here indicating the origin of type “B” fibers from the nucleus lateralis tuberis (NLT). Type “A” fibers appear to be related to the storage of neurohypophysial hormones, while type “B” fibers seem to store two principles, a catecholamine and a protein. New histophysiological data are presented here suggesting a regulatory participation of type “B” fibers in gonadotropic and prolactin cell activities. Finally, a brief summary of the anatomy of the hypothalamo-hypophysial relationships in the lungfish Lepidosiren paradoxa is presented. The coexistence of peptidergic fibers ending on portal vessels of the median eminence together with a direct aminergic innervation of the glandular cells of the adenohypophysis is described.