Figure 6.

Proposed differential CB1 regulation of collateral (GABA) inputs and cortical (glutamate, Glu) inputs to striatal projection neurons in associative/limbic vs. sensorimotor corticostriatal circuits. The proposed number of CB1 receptors on afferent terminals (see text) is indicated by the size of squares. Our present findings indicate an inverse relationship between cortical and striatal CB1 expression in associative/limbic circuits with inputs from medial prefrontal cortex (mPFCx) (left) and sensorimotor circuits (right), with relatively high cortical and low striatal CB1 expression in the former and low cortical and high striatal expression in the latter. It is argued that, in sensorimotor corticostriatal circuits, striatal CB1 receptors are mainly located presynaptically on local axon collateral terminals of projection neurons (open triangles) and regulate GABA release from these terminals (see text). On the other hand, striatal CB1 receptors in associative/limbic circuits may mostly regulate excitatory inputs from the cortex (filled triangles) and other areas (and GABA inputs from interneurons; not shown). The degree of shading in striatal areas and respective neurons reflects the amount of CB1 receptor expression in these neurons. The black dots symbolize endocannabinoid release from striatal neurons. SMCx, sensorimotor cortex.