DOPAMINERGIC INFLUENCE ON THE EXCITABILITY OF ANTIDROMICALLY ACTIVATED RENSHAW CELLS IN THE LUMBAR SPINAL-CORD OF THE RAT

The interaction between dopaminergic and cholinergic systems in the ma mmalian central nervous system, which is thought to have important imp lications in the pathophysiology of major extrapyramidal disorders, ha s never been adequately demonstrated in vivo. Renshaw cell burst respo nses to single electrical shocks to lumbar ventral roots in spinalized and decerebrated rats were studied. In this monosynaptic cholinergic pathway, apomorphine, a dopaminergic receptor agonist, inhibited where as the D2-antagonist sulpiride facilitated the burst responses. The mu tual antagonism of the two drugs and the depression coupled with the f aster decay of post-tetanic potentiation of Renshaw cells by apomorphi ne demonstrate the involvement of presynaptic D2-receptors through whi ch dopamine can modulate acetylcholine-mediated central synaptic trans mission in vivo. The study also provides further evidence for the invo lvement of the spinal cord in extrapyramidal disorders.