Electron microscopic observation of substance P-like immunoreactive nerve fibres and innervation in the anterior pituitary of macaques.

The anterior pituitary has recently been confirmed to be innervated by substance P-immunoreactive nerve fibres in the monkey and human. The present study investigated the morphology of the nerve fibres and their relationship with anterior pituitary gland cells in the macaque by means of immunoelectron microscopy. Many substance P-immunoreactive and unlabelled nerve fibres were distributed among the gland cells or formed nerve fibre bundles. These nerve fibres were unmyelinated and varicose, and contained a great many clear and/or large dense-cored vesicles. Substance P-immunoreactive cells were seen in the pars distalis of the anterior pituitary. Direct contacts between these nerve fibres and every cell type of the gland could be ascertained, including substance P-immunoreactive cells. Synaptoid contacts were seen among the substance P-immunoreactive varicosities and somatotropes, opiocortico-melanotropes and folliculostellate cells. Typical synapses were identified in somatotropes and opiocortico-melanotropes.