1995 Volume 7 Issue 2 Pages 183-192
Catecholaminergic innervation of the rat neurohypophysis was studied by electron-microscopic immunocytochemistry for tyrosine hydroxylase using the preembedding peroxidase-antiperoxidase method. Examination of semithin sections of the neuro-intermediate lobe of the pituitary showed that most of the nerve fibers and terminals that displayed tyrosine hydroxylase (TH) -like immunoreactivity were in the parenchyma of the neurohypophysis, and that some of them were in close contact with pituicytes. Ultrastructurally, the TH-like immunoreactive (LI) terminals contained many small, clear vesicles and mitochondria in addition to some dense-core granules and large, clear vesicles. The reaction products were located around all of the membranous structures and within the dense-core granules. The TH-LI terminals were found to make synapse-like contacts with magnocellular neurosecretory fibers and terminals as well as with cell bodies and processes of pituicytes. At the sites of the synapse-like contacts, aggregations of small, clear vesicles in the presynaptic TH-LI terminal were seen. The present results provide ultrastructural evidence of catecholaminergic regulatory influence on some functions of magnocellular neurons and pituicytes in the neurohypophysis. The functional significance of the synapse-like contacts with special reference to neurosecretory hormone release in the neurohypophysis is discussed.
