Dopaminergic neurons in sympathetic ganglia of the dog

Abstract

A study has been made of the catecholamine content of various canine sympathetic ganglia. The data have been related to the anatomical location of ganglion cells supplying the kidney and hindpaw. Retrograde transport of horseradish peroxidase from filaments of the renal nerve labelled cell bodies in the ipsilateral renal and superior mesenteric ganglia and in one to three contiguous ganglia of the lower thoracic paravertebral chain. In most prevertebral and paravertebral ganglia, the ratio of the tissue level of dopamine (DA) to that of noradrenalin (NA) lay between 3 and 7%. The relative DA levels were significantly higher (DA: NA = 8–20%) in one to three paravertebral ganglia of the lower thoracic and the sacral regions. In some animals, the relative DA levels in renal and/or coeliac and superior mesenteric ganglia were also greater than the mean paravertebral values for these individuals. Reserpine pretreatment depleted DA and NA stores and abolished or substantially reduced catecholamine fluorescence in all ganglia. After reserpine pretreatment followed by administration of a monoamine oxidase inhibitor and l ─DOPA, fluorescence was restored to some neurons in ganglia corresponding to those normally having raised DA levels. This local restoration of fluorescence was correlated with a dramatic increase in the relative amount of DA in equivalent contralateral ganglia (DA: NA = 50–280%). These results suggest that: (i) some catecholamine-containing ganglion cells are distinct from sympathetic noradrenergic neurons in their high content of DA and their ability to bind dopamine following reserpine-induced depletion, and (ii) these neurons are relatively restricted in their distribution, lying between T8 and L1 and L7 and S2 of the paravertebral chain and in some prevertebral ganglia. They occur at locations in which ganglion cells projecting to the kidney and the hindlimb are likely to be represented. Our results are consistent with pharmacological evidence that has been presented elsewhere that renal juxtaglomerular vessels and arteriovenous shunts of the hindpaw are supplied by dopaminergic dilator axons. They also suggest that some other peripheral effectors in the upper abdomen may be innervated by dopaminergic axons.