Effects of drugs stimulating and blocking M and N cholinergic receptors on GABA level and GAD activity in rat cerebral cortex.

In the experiments carried out on Wistar rats it was demonstrated that pilocarpine was without effect on the GABA level in the cerebral cortex, while physostigmine raised this level. These changes were prevented by atropine. Lobeline and nicotine exerted a biphasic effect on GABA level: in small doses given 15 min before decapitation they decreased, and in higher doses and after longer time intervals they increased this level. This was due to their biphasic action on the cholinergic receptor N. Changes in GABA level produced by stimulation of the N receptor by lobeline and nicotine were prevented by mecamylamine, d-tubocurarine, and in part also by atropine, phentolamine and propranolol. This suggests an indirect participation of alpha and beta receptors in the transmission of impulses from the cholinergic N receptors to the GABA-ergic system. The effect of the tested substances on GAD activity was not uniform. No close correlation was demonstrated between GAD activity and GABA level.