Distinct preganglionic neurons innervate noradrenaline and adrenaline cells in the cat adrenal medulla

Calretinin immunoreactivity was present in a subset of preganglionic neurons retrogradely labelled from the cat adrenal gland. Overall, one-third of adrenal preganglionic neurons showed calretinin immunoreactivity, and their proportion increased in the more caudal spinal cord segments. Calretinin-immunoreactive nerve terminals were prominent within the adrenal gland, but were found only in areas of noradrenergic chromaffin cells (approximately one-third of the area of the adrenal medulla). Synaptophysin immunoreactivity was used to label terminals with and without calretinin immunoreactivity. Nerve terminals lacking calretinin immunoreactivity were present among the adrenergic chromaffin cells and also comprised 20% of the nerve terminals innervating noradrenergic chromaffin cells. Calretinin immunoreactivity thus labels a subpopulation of cat adrenal preganglionic neurons that innervate the noradrenergic chromaffin cells.