M5 Muscarinic Receptors Mediate Striatal Dopamine Activation by Ventral Tegmental Morphine and Pedunculopontine Stimulation in Mice
Figure 2
Changes in accumbal dopamine efflux produced by 50 ng intra-VTA morphine or saline in wildtype (+/+) or M5 knockout (−/−) mice.
In all cases, thick lines represent mean dopamine oxidation current across mice, and thin lines represent ±SEM. (A) Mean change in accumbal dopamine efflux in wildtype mice following 50 ng intra-VTA morphine (black line, n = 4) or 0.3 µl intra-VTA saline (gray line, n = 4). (B) Mean change in accumbal dopamine efflux in M5 knockout mice following 50 ng intra-VTA morphine (black line, n = 4) or 0.3 µl intra-VTA saline (gray line, n = 4). (C) Effects of pre-treatment with 50 µg intra-VTA scopolamine on accumbal dopamine efflux induced by 50 ng intra-VTA morphine in wildtype mice (black line, n = 6). For comparison, data from (A) showing mean changes in accumbal dopamine efflux induced by 50 ng intra-VTA morphine without any pre-treatment in wildtype mice are reproduced (gray line, n = 4). (D) Effects of pre-treatment with naltrexone (1 mg/kg, i.p.) 5 min prior to 50 ng intra-VTA morphine in wildtype mice (black line, n = 4). For comparison, data from (A) showing mean changes in accumbal dopamine efflux induced by 50 ng intra-VTA morphine without any pre-treatment in wildtype mice are reproduced (gray line, n = 4).