Immunohistochemical localization of cannabinoid CB1 receptor in inhibitory interneurons in the cerebellum.

Inhibitory interneurons terminating on Purkinje cell dendrites contribute to cannabinoid-mediated cerebellar plasticity, consistent with the intense expression of cannabinoid CB1 receptor protein in the cerebellar molecular layer. CB1 labelling in the molecular layer has been attributed to parallel fibers originating from granule cells, climbing fibers originating in the inferior olive, and inhibitory interneurons in the deep molecular layer (basket cells). However, the cellular distribution of CB1 in the cerebellar molecular layer has remained poorly understood. We used double fluorescence labelling to test for co-localization of nuclei with CB1 receptor protein. Labelling was intense surrounding nuclei in the deep and superficial molecular layer; consistent with basket cell and stellate cell inhibitory interneurons that regulate depolarization-induced suppression of inhibition (DSI) of Purkinje cells.