Abstract

Atrial cardiac ganglia of rats, cats, guinea pigs and mice were studied for catecholamine-containing structures by a histochemical fluorescence method. Very fine varicose adrenergic fibers were seen in close apposition to some of the cholinergic ganglion cells. The administration of a monoamine oxidase inhibitor followed by 3,4-dihydroxyphenylalanine. resulted in the appearance of catecholamine (CA) fluorescence in some ganglion cells. This suggests that at least some parasympathetic cells are capable of taking up 3,4-dihydroxyphenylalanine and synthesizing and metabolizing CA. Intense CA-fluorescent cells resembling adrenal medullary cells were found in the confines of the atrial ganglia of all species. Positive chromaffin and silver-staining reactions were observed in these cells of the cat atria. The cells are considered to be chromaffin cells and as such can be regarded as an extraneuronal CA pool. One dose of reserpine (5 mg/kg) administered 24 or 4 hr before sacrifice does not appear to affect the CA content of the chromaffin cells. Larger doses of reserpine for a longer period of time lead to a reduction in the intensity of fluorescence of the chromaffin cells. Application of both the CA-fluorescent and acetylcholinesterase histochemical stains to the same section revealed that most chromaffin cellsare innervated by acetylcholinesterase-staining nerve fibers. Some chromaffin cells receive a postganglionic parasympathetic innervation from cholinergic ganglion cells of the heart. It is suggested that the system of adrenergic fibers and chromaffin cells contained around cardiac ganglia functions as a self-controlling or inhibitory influence on ganglionic transmission.