Ultrastructural localization of nerve terminals containing nitric oxide synthase in rat adrenal gland.

Immunoelectron microscopy was performed to localize immunoreactivity for nitric oxide synthase (NOS) in rat adrenal gland. NOS-immunoreactive (NOS-ir) nerve fibers were observed around blood vessels and endocrine cells in the zona glomerulosa of the cortex. Electron microscopy showed that NOS-ir axon varicosities were in close contact with the smooth muscles of blood vessels and with the cytolemma of endocrine cells. In the adrenal medulla, several NOS-ir ganglion cells were found. Synaptic contacts between non-immunoreactive axons and dendrites of NOS-ir neurons were observed. NOS-ir nerve fibers were distributed among chromaffin cells. Positive axon varicosities were in close contact with the catecholamine-storing chromaffin cells. These results suggest that NOS-ir nerve cells control directly the secretion of corticosteroid and catecholamine in addition to the vascular tone.