To identify the role of mAChRs on DA release evoked by endogenous cholinergic activity, we next tested the effect of the mAChR antagonist scopolamine on DA levels triggered by selective stimulation of CINs. When scopolamine (1 μM) was applied to the bath, DA peak levels evoked by a single pulse of selective CIN stimulation only modestly increased to 112 % of pretreatment values; p = 0.38. When CINs were optically stimulated by a train of 30 pulses at 10 or 5 Hz (10 mW, 4 msec duration per pulse), peak DA levels significantly increased to 146-148 %, p < 0.05) of pretreatment values (n=6-12) (Fig. 3E,F) suggesting that blocking mAChRs relieves the inhibition of ACh release and that this effect is preferentially seen when trains of action potentials drive mobilization of the ACh releasable pool.
