DOPAMINE AS TRACE AMINE IN THE DORSAL-ROOT GANGLIA

It has been shown that in the chick dorsal root ganglion (DRG) about 8 % of neurons, belonging to both the A and B classes of sensory neurons exhibit a clear dopamine immunoreactivity. In the present study are r eported the results of measurements, by mean of HPLC-electrochemical d etection (HPLC-ED), of DA and of the DA metabolites dihydroxyphenylace tic acid (DOPAC) and homovanillic acid (HVA) in the rat DRG and their central nerves. Very low levels of DA, about 10 folds lower than the l evels found in the dorsal horn of the spinal cord, were found in the D RG. However the levels of DOPAC and HVA were approximately equivalent to the levels found in the cord. The immunocytochemical study performe d in parallel has shown that some dopaminergic-immunoreactive fibers i n the DRG are located around the blood vessels. Few dopamine-immunorea ctive sensory neurons were identified in the DRG and immunoreactive fi bers, not linked to blood vessels, were identified in the dorsal root nerves. The present work indicates that there is a dopaminergic innerv ation of the blood vessels in the rat DRG but that dopamine may also b e, as in the chick, a transmitter of primary afferent fibers.