Expression of functional cannabinoid CB2 receptor in VTA dopamine neurons in rats.

We have recently reported the expression of functional cannabinoid CB2 receptors (CB2 Rs) in midbrain dopamine (DA) neurons in mice. However, little is known whether CB2 Rs are similarly expressed in rat brain because significant species differences in CB2 R structures and expression are found. In situ hybridization and immunohistochemical assays detected CB2 gene and receptors in DA neurons of the ventral tegmental area (VTA), which was up-regulated in cocaine self-administration rats. Electrophysiological studies demonstrated that activation of CB2 Rs by JWH133 inhibited VTA DA neuronal firing in single dissociated neurons. Systemic administration of JWH133 failed to alter, while local administration of JWH133 into the nucleus accumbens inhibited cocaine-enhanced extracellular DA and i.v. cocaine self-administration. This effect was blocked by AM630, a selective CB2 R antagonist. These data suggest that CB2 Rs are expressed in VTA DA neurons and functionally modulate DA neuronal activities and cocaine self-administration behavior in rats.