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K.M. Studholme, S. Zimov, A. Torre–Healy, S. Yazulla; Immunolocalization of Endocannabinoid Degradative Enzymes FAAH, MGL and COX–2 in Mouse Retina . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5382.
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© ARVO (1962-2015); The Authors (2016-present)
The regulation of endocannabinoids (eCB), anandamide (AEA) and 2–arachidonylglycerol (2–AG), depends, in part on the distribution of their degradative enzymes that include: fatty acid amide hydrolase (FAAH), monoglyceride lipase (MGL) and cyclooxygenase–2 (COX–2). AEA is mostly degraded by FAAH, while 2–AG is mostly degraded by MGL. Both AEA and 2–AG are oxidized by COX–2, but the relative importance in vivo is unknown. The distributions of FAAH, MGL and COX–2 in mouse retina were determined by immunocytochemistry.
Immunofluorescence was used to detect immunoreactivity (IR) against FAAH, MGL and COX–2 antisera in cryostat sections of C57/BL6 mouse retina. Labeling was abolished after preadsorption with peptide antigen.
FAAH–IR was prominent in all ganglion cells in the ganglion cell layer (GCL) over rod bipolar cell bodies, rod nuclei and with lighter label over amacrine cell bodies in the proximal inner nuclear layer (INL) and in a band in the middle of the inner plexiform layer (IPL). MGL–IR was prominent over ganglion cell bodies, in bipolar cell bodies in the distal INL and in a sparse population of large amacrine cells at the proximal margin of the INL. There was total colocalization between MGL–IR and PKC–IR in rod bipolar cells. However, the large MGL–IR amacrine cells did not label for either PKC–IR nor for TOH–IR, demonstrating that MGL–IR labeled an third type of large, rare amacrine cell. COX–2–IR was sporadically granular in bipolar cell bodies, but intense in the bipolar cell axons. There also was a diffuse label throughout the IPL. There was extensive colocalization of COX–2–IR and PKC–IR in rod bipolar cells. However, there were bipolar cells that stained for only PKC or only for COX–2, suggesting that rod bipolar cells constituted two neurochemical subtypes: PKC only (1/3) and PKC/COX–2 (2/3). One–third of the COX–2–IR bipolar cells were COX–2 only and were likely to be cone bipolar cells.
Three degradative enzymes for eCB are well represented in mouse retina, suggesting that two endocannabinoids, AEA and 2–AG are present. The predominance of FAAH and MGL in ganglion cells in contrast to COX–2 in bipolar cells, suggests differential localization and regulation of eCBs in the retina. Finally, it appears that rod bipolar cells are not of a single neurochemical type, but rather can be differentiated as to whether or not they contain COX–2.
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