Light and electron microscopy of the adrenal medulla of macaca mulata monkey

Abstract The fine structure of the adrenal medulla of Macaca mulata monkey was studied after double fixation with paraformaldehyde and OsO 4 ; other fixations were employed for comparison. Only one cell type was seen. The cytoplasm contained an uneven distribution of chromaffin vesicles which were either spherical or elongated and 0.1–0.3 μ in diameter. There were two principle vesicle categories: dark and compact forms which comprised the majority (about 80%) and lighter, mostly larger, vesicles with a finely granulated appearance. The Golgi apparatus was often seen in relatively clear areas where few other organelles were present. Vesicles, 0.1–0.2 μ in diameter, which stained heterogeneously were also observed. They were few in number and always associated with the Golgi apparatus. The chromaffin cells lay in close proximity, but in no specific relationship, to thin‐walled blood vessels. Nerve endings which were partially embraced by Schwann cells were in synaptic relation to the chromaffin cells. These findings are compared with previous observations in other mammals and the nature of the dark and light vesicles is discussed.