Revaluation of neuronal contacts with pituicytes in the rat posterior pituitary

Synaptic structures of neuronal contacts with pituicytes in the posterior pituitary (PP) were investigated in detail after wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) injection into the rat hypothalamus including the paraventricular, dorsomedial and arcuate nuclei. The injection resulted in heavy labeling of hypothalamic fibers in the PP. In the neuropil of the PP, there were a lot of terminals containing HRP-reaction product (RP) recognized as electron dense lysosomal-like structures. It was of particular interest that the terminals make synaptic contacts with pituicytes. Although the neuronal contacts were characterized by the structure of presynaptic thickening, occasionally two classes could be distinguished asymmetrical and symmetrical synaptic contacts (Gray’s type I and II). These findings provided the morphological evidence for tight structural relationship of neurons with pituicytes in the PP, as well as neuro-neuronal connections in the central nervous system, and additionally for pituicyte modulation of neurohormone output.