Effect of scopolamine plus physostigmine co-administration or mecamylamine plus physostigmine co-administration on immobility time in the FST. A. VTA scopolamine plus physostigmine experiment. Intra-VTA physostigmine administration increased immobility time in the FST (p < 0.05, Tukey post-hoc of 2 μg/side physostigmine versus saline), but co-administration with scopolamine blocked the physostigmine-induced increase in immobility (p < 0.05, Tukey post-hoc of 2 μg/side physostigmine plus 24 μg/side scopolamine versus scopolamine alone; p > 0.05, Tukey post-hoc of 2 μg/side physostigmine plus 24 μg/side scopolamine versus saline). B. VTA mecamylamine plus physostigmine experiment. Intra-VTA 2 μg/side physostigmine (in a separate cohort from that in panel A) increased immobility time in the FST (p < 0.05, Tukey post-hoc of 2 μg/side physostigmine versus saline). Intra-VTA 30 μg/side mecamylamine co-administration with 2 μg/side physostigmine did not alter the physostigmine-induced increase in immobility time (p > 0.05, Tukey post-hoc of 2 μg/side physostigmine plus 30 μg/side mecamylamine versus to 2 μg/side alone; p < 0.05, Tukey post-hoc of 2 μg/side physostigmine plus 30 μg/side mecamylamine versus saline). C. Systemic 0.125 mg/kg physostigmine plus intra-VTA mecamylamine or scopolamine experiment. Systemic administration of physostigmine led increased immobility time (p < 0.001, Tukey post-hoc of 2 μg/side physostigmine versus saline). Intra-VTA infusion of 30 μg/side mecamylamine co-administered with systemic 0.125 mg/kg physostigmine also increased immobility time compared to saline administered rats (p < 0.05, Tukey post-hoc), with no difference between physostigmine alone versus physostigmine plus mecamylamine (p > 0.05, Tukey post-hoc). Intra-VTA infusion of 24 μg/side scopolamine co-administered with systemic 0.125 mg/kg physostigmine increased immobility time compared to control rats (p < 0.05, Tukey post-hoc), with no difference between physostigmine alone versus physostigmine plus scopolamine (p > 0.05, Tukey post-hoc). D. Histological verification of cannula placements. Dark filled circles indicate representative placements for the scopolamine plus physostigmine experiments. Light filled circles indicate representative placements for the mecamylamine plus physostigmine experiments.