The present immunohistochemical and enzyme histochemical study showed gamma
-aminobutyric acid (GABA) immunoreactivity and acetylcholinesterase (AChE)
activity in the mouse adrenal gland. Weak GABA immunoreactivity was seen in
clusters of chromaffin cells showing noradrenaline fluorescence. This find
ing suggests that both GABA and noradrenaline may be released from the gran
ules of noradrenaline cells by adequate stimuli. GABA-immunoreactive varico
se nerve fibers densely contacted adrenaline cells and large ganglion cells
, but they were sparse in the periphery of clusters of noradrenaline cells.
AChE activity was strong in a few large ganglion cells and weak in chromaf
fin cells showing noradrenaline fluorescence, and was found in numerous ner
ve bundles and fibers of the medulla. AChE-active nerve fibers more densely
contacted noradrenaline cells than adrenaline cells. By using double label
ing technique, numerous GABA-immunoreactive nerve fibers in the medulla wer
e reactive for AChE in the same sections. These results suggest that both G
ABA and acetylcholine may be colocalized in the intra-adrenal nerve fibers
and may have some secretory effects on the chromaffin cells.