Nicotinic Receptor Alpha7 Expression during Mouse Adrenal Gland Development

The nicotinic acetylcholine receptor alpha 7 (α7) is a ligand-activated ion channel that contributes to a diversity of cellular processes involved in development, neurotransmission and inflammation. In this report the expression of α7 was examined in the mouse developing and adult adrenal gland that expresses a green fluorescent protein (GFP) reporter as a bi-cistronic extension of the endogenous α7 transcript (α7 G ). At embryonic day 12.5 (E12.5) α7 G expression was associated with the suprarenal ganglion and precursor cells of the adrenal gland. The α7 G cells are catecholaminergic chromaffin cells as reflected by their progressive increase in the co-expression of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) that is complete by E18.5. In the adult, α7 G expression is limited to a subset of chromaffin cells in the adrenal medulla that cluster near the border with the adrenal cortex. These chromaffin cells co-express α7 G , TH and DBH, but they lack phenylethanolamine N-methyltransferase (PNMT) consistent with only norepinephrine (NE) synthesis. These cell groups appear to be preferentially innervated by pre-ganglionic afferents identified by the neurotrophin receptor p75. No afferents identified by beta-III tubulin, neurofilament proteins or p75 co-expressed α7 G . Occasional α7 G cells in the pre-E14.5 embryos express neuronal markers consistent with intrinsic ganglion cells and in the adult some α7 G cells co-express glutamic acid decarboxylase. The transient expression of α7 during adrenal gland development and its prominent co-expression by a subset of NE chromaffin cells in the adult suggests that the α7 receptor contributes to multiple aspects of adrenal gland development and function that persist into adulthood.