Opposite function of dopamine D1 and N-methyl-D-aspartate receptors in striatal cannabinoid-mediated signaling.
It is well established that the cannabinoid and dopamine systems interact at various levels to regulate basal ganglia function. Although it is well known that acute administration of cannabinoids to mice can modify dopamine-dependent behaviors, the intraneuronal signaling pathways employed by these agents in the striatum are not well understood. Here we used knockout mouse models to examine the regulation of striatal extracellular-signal-regulated kinases 1 and 2 (ERK12) signaling by behaviorally relevant doses of cannabinoids. This cellular pathway has been implicated as a central mediator of drug reward and synaptic plasticity. In C57BL6J mice, acute administration of the cannabinoid agonists, (-)-11-hydroxydimethylheptyl-Δ8-tetrahydrocannabinol (HU-210) and delta-9-tetrahydrocannabinol (Δ(9) -THC), promoted a dose- and time-dependent decrease in the phosphorylation of ERK12 in dorsal striatum. Co-administration of the CB1 cannabinoid receptor antagonist N-(Piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide(AM251) with HU-210 prevented ERK12 inactivation, indicating a requirement for activation of this receptor. In dopamine D1 receptor knockout animals treated with HU-210, the magnitude of the HU-210-dependent decrease in striatal ERK12 signaling was greater than in wild-type controls. In contrast, HU-210 administration to N-methyl-D-aspartate receptor knockdown mice was ineffective at promoting striatal ERK12 inactivation. Genetic deletion of other potential ERK12 mediators, the dopamine D2 receptors or β-arrestin-1 or -2, did not affect the HU-210-induced modulation of ERK12 signaling in the striatum. These results support the hypothesis that dopamine D1 receptors and N-methyl-D-aspartate receptors act in an opposite manner to regulate striatal CB1 cannabinoid receptor signal transduction.