Microscopic anatomy of the baboon (Papio hamadryas) adrenal medulla

Adrenal medullas of 2 baboons perfused with formaldehyde/glutaraldehyde and tannic acid were studied by light and electron microscopy. Tissues were postfixed in OsO4. This procedure allows identification of noradrenaline cells on the basis of a selective reaction of glutaraldehyde with noradrenaline vesicles. As positive control for noradrenaline cells, similarly treated mouse adrenal medullas were also examined. Light microscopic examination of thick sections of baboon medullas did not show noradrenaline cells. In contrast, mouse adrenal medullas showed noradrenaline cells scattered in small groups among the much lighter adrenaline cells. By electron microscopy no noradrenaline cells were seen in the baboon medulla while mouse adrenal medullas showed noradrenaline cells with vesicles possessing exceedingly dense cores and light spaces within their limiting membranes. Otherwise, the majority of the baboon chromaffin cells showed chromaffin vesicles which were round or elongated, 150-520 nm in diameter, and heterogenous in electron density. Cytoplasmic densities were occasionally seen attached to the inner aspect of the plasmalemma, particularly along areas close to blood capillaries. These densities could be chromaffin vesicles in the process of exocytosis. This is the first report of exocytotic profiles in a primate medulla. Occasional small vesicle-containing cells also were present. The vast majority of their vesicles were electron dense. Several possible alternatives for the varied catecholamine vesicular osmiophilia, were discussed. It was suggested that this could be attributed to varied concentration of noradrenaline and adrenaline neurohormones among the vesicle population.