Increased plasma catecholamines and locomotor activity induced by centrally administered substance P in guinea-pigs

The effects on locomotor activity and plasma catecholamines of substance P, 0.5 nmol, injected into each lateral ventricle (i.c.v.), or 1 nmol, injected into the cisterna magna of conscious guinea-pigs, were investigated. Locomotor activity was measured in cages fitted with an infra-red photocell and detector, and plasma catecholamines, were measured by HPLC with electrochemical detection. Substance P, given intraventricularly or into the cisterna magna, produced increased locomotor activity and a pattern of behavioural activity which mimicked the opiate withdrawal response, found in previous studies in this species. Levels of NA and AD in plasma were also significantly elevated after injection of substance P. These effects of substance P were relatively long-lasting, since they were present up to 1 hr after injection. The results show that the effects of centrally administered substance P in guinea-pigs are similar to those in rats. Furthermore, the results support the suggestion that substance P might be the mediator of the opiate withdrawal response in the central nervous system as has been proposed for the enteric nervous system.