PC12 cells as a window for the differentiation of neural crest into adrenergic nerve ending and adrenal medulla.

Studies on PC12 and isolated adrenal chromaffin cells have revealed that PC12 cells have a closer identity to the adrenergic nerve ending than do the chromaffin cells. This is revealed by the presence of monoamine oxidase (MAO) A and tyramine-released pool of catecholamines in PC12, resembling that in adrenergic neurones, and their absence in adrenal chromaffin cells. Indeed, chromaffin cells possess primarily MAO-B activity. Like the observations on adrenergic neurones, non-selective and selective MAO-A inhibitors potentiate the catecholamine-releasing property of tyramine in PC12 cells. This property has clearly been demonstrated to be associated with selective inhibition of MAO-A and not MAO-B. The fact that MAO-A and MAO-B are different proteins and under separate gene product control suggests that their regulation may be highly differentiated. Indeed, it has been shown that while steroids such as progesterone and hydrocortisone induce and estrogen diminishes MAO-A activity in PC12 cells, no such regulatory mechanism has been identified for MAO-B activity in chromaffin cells. In the final analysis the inter-relationship between MAO-A activity and the presence of tyramine-releasable pool of catecholamines in adrenergic neurons and PC12 cells may have a genetic basis and could be important in illuminating the differentiation of neural crest into adrenergic neurones and adrenal medulla on the one hand and chromaffin cells to PC12 cells on the other.