CHOLINERGIC MODULATION OF SYNAPTIC TRANSMISSION IN HORIZONTAL CONNECTIONS OF RAT MOTOR CORTEX

The influence of compounds interacting with cholinergic systems on fie ld potentials evoked in layer II/III horizontal connections was invest igated in rat motor cortex in vitro. The cholinesterase inhibitor eser ine (10 mu M) decreased field responses by 20 +/- 2%. This effect coul d be prevented by preincubation with atropine (10 mu M). Application o f 5 mu M carbachol resulted in reduction of the responses by 30 +/- 1% . These reductions were reversible, repeatable and independent of stim ulus intensity; they could be blocked by the M1 muscarinic receptor an tagonist pirenzepine (3 mu M) but not by the M2 muscarinic receptor an tagonist gallamine (10 mu M) During carbachol application, paired-puls e facilitation (40 ms interpulse interval) was increased. The results indicate that endogenous acetylcholine may modulate excitatory synapti c transmission in horizontal connections of rat motor cortex, most lik ely by acting upon MI receptors located presynptically on glutamatergi c terminals, and may contribute both to information processing and syn aptic plasticity within the motor cortex.