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

In the experiments on Wistar rats it was demonstrated that pilocarpine and physostigmine decreased the GABA level in the striatum. This change was prevented by atropine. Lobeline and nicotine exerted a biphasic effect on GABA level: given in small doses 15 min before decapitation they raised, and in higher doses they decreased this level. This was due to their biphasic effect on the cholinergic receptor N. The changes in GABA level produced by stimulation of N receptors by lobeline and nicotine were prevented by mecamylamine and d-tubocurarine, and in part also by atropine and propranolol. This suggests an indirect participation of M and beta receptors in the transmission of impulses from the cholinergic receptors N to the GABA-ergic system. The effect of the tested substances on GAD activity was not uniform. No strict correlation was demonstrated between GAD activity and GABA level.