Ultrastructure of the sturgeon neurohypophysis

Three types of nerve fibres and their terminals have been revealed in the sturgeon neurohypophysis. Peptidergic A1 and A2 type fibres contain granules 120--200 and 100--160 nm in diameter, resp. Monoaminergic B type fibres have granules 80-100 nm in diameter. Terminals of A2 type predominate in the sturgeon neurohypophysis, A1 and B type terminals are a rarer occurrence. Different stages of exocytosis of the neurosecretory granule content were seen in the A1 and A2 type terminals. It is suggested that neurosecretory granules are the carriers of arginine-8-vasotocin and oxytocin-like polypeptide in A2 and A1 fibres, resp.