Dual Neurosecretory Innervation of the Adenohypophysis of Hippocampus, the Sea-horse

Abstract

THE postulate that a dual control of endocrine function by two kinds of neurosecretory fibre may be a fundamental feature of neuroendocrine systems¹ has received much support in recent years^2–4. It has been suggested that type A fibres, containing peptide hormones, and type B fibres, containing monoamines, may regulate intrinsic endocrine cells of the pituitary. Direct synaptoid contacts (that is, contacts which morphologically resemble synapses elsewhere in the central nervous system) have been demonstrated in an elasmobranch fish, but so far only in the pars intermedia². In a teleost fish, the eel, type A and type B fibres invade all lobes of the pituitary⁴. In this fish the fibre terminals are separated from the intrinsic cells of the pars distalis by vascular channels, and so a morphological proof that pars distalis function in teleosts is under dual neurosecretory control was still incomplete. This problem has now been investigated in Hippocampus. This species was chosen because it has been shown by Da Lage⁵, using light microscopy, that neurosecretory fibres are closely associated with pars distalis cells.