Gamma aminobutyric acid immunoreactivity in the mouse adrenal gland during postnatal development

To understand the developing processes of gamma-aminobutyric acid (GABA)-containing chromaffin cells and nerve fibers in the mouse adrenal gland, we examined the tissues in various postnatal stages by immunohistochemistry using a GABA antibody. From birth until postnatal week 1, GABA-immunoreactivity was seen in very few nerve fibers, and in none of the chromaffin cells. At postnatal week 2, GABA-immunoreactivity appeared weakly in clusters of chromaffin cells and strongly in relatively numerous varicose nerve fibers. The immunoreactive nerve fibers were densely distributed in the small immunonegative chromaffin cells and large ganglion cells, but only sparsely so in the weak immunoreactive chromaffin cells. At postnatal week 3, the number of the immunoreactive chromaffin cells and nerve fibers further increased compared to that at postnatal week 2. The staining pattern of GABA-immunoreactive nerve fibers in the medullas was similar to that at postnatal week 2. From postnatal week 4 until postnatal week 8, the distribution and frequency of the immunoreactive chromaffin cells and nerve fibers were also similar to those at postnatal week 3. These results suggest that the expression of GABA in the chromaffin cells and in the nerve fibers of the mouse adrenal gland may be completed by postnatal week 3.