Immunocytochemical localization of cannabinoid CB1 receptor and fatty acidamide hydrolase in rat retina

Cannabinoids have major effects on central nervous system function. Recent studies indicate that cannabinoid effects on the visual system have a retin al component. Immunocytochemical methods were used to localize cannabinoid CB1 receptor immunoreactivity (CB1R-IR) and an endocannabinoid (anandamide and 2-arachidonylglycerol) degradative enzyme, fatty acid amide hydrolase ( FAAH)-IR, in the rat retina. Double labeling with neuron-specific markers p ermitted identification of cells that were labeled with CB1R-IR and FAAH-IR . CB1R-IR was observed in all cells that were protein kinase C-immunoreacti ve (rod bipolar cells and a subtype of GABA-amacrine cell) as well as horiz ontal cells (identified by calbindin-IR). There was also punctate CB1R-IR i n the distal one-third of the inner plexiform layer (IPL) that could not be assigned to a cell type. FAAH-IR was most prominent in large ganglion cell s, whose dendrites projected to a narrow band in the proximal IPL. Weaker F AAH-IR was observed in the soma of horizontal cells (identified by calbindi n-IR); the soma of large, but not small, dopamine amacrine cells (identifie d by tyrosine hydroxylase-IR); and dendrites of orthotopic- and displaced-s tarburst amacrine cells (identified by choline acetyltransferase-IR) but in less than 50% of the starburst amacrine cell somata. The extensive distrib ution of CB1R-IR on horizontal cells and rod bipolar cells indicates a role of endocannabinoids in scotopic vision, whereas the more widespread distri bution of FAAH-IR indicates a complex control of endocannabinoid release an d degradation in the retina. (C) 1999 Wiley-Liss. Inc.