Localization of the cannabinoid CB1 receptor and the 2-AG synthesizing (DAGLα) and degrading (MAGL, FAAH) enzymes in cells expressing the Ca(2+)-binding proteins calbindin, calretinin, and parvalbumin in the adult rat hippocampus.

The retrograde suppression of the synaptic transmission by the endocannabinoid sn-2-arachidonoylglycerol (2-AG) is mediated by the cannabinoid CB1 receptors and requires the elevation of intracellular Ca(2+) and the activation of specific 2-AG synthesizing (i.e., DAGLα) enzymes. However, the anatomical organization of the neuronal substrates that express 2-AG/CB1 signaling system-related molecules associated with selective Ca(2+)-binding proteins (CaBPs) is still unknown. For this purpose, we used double-label immunofluorescence and confocal laser scanning microscopy for the characterization of the expression of the 2-AG/CB1 signaling system (CB1 receptor, DAGLα, MAGL, and FAAH) and the CaBPs calbindin D28k, calretinin, and parvalbumin in the rat hippocampus. CB1, DAGLα, and MAGL labeling was mainly localized in fibers and neuropil, which were differentially organized depending on the hippocampal CaBPs-expressing cells. CB(+) 1 fiber terminals localized in all hippocampal principal cell layers were tightly attached to calbindin(+) cells (granular and pyramidal neurons), and calretinin(+) and parvalbumin(+) interneurons. DAGLα neuropil labeling was selectively found surrounding calbindin(+) principal cells in the dentate gyrus and CA1, and in the calretinin(+) and parvalbumin(+) interneurons in the pyramidal cell layers of the CA1/3 fields. MAGL(+) terminals were only observed around CA1 calbindin(+) pyramidal cells, CA1/3 calretinin(+) interneurons and CA3 parvalbumin(+) interneurons localized in the pyramidal cell layers. Interestingly, calbindin(+) pyramidal cells expressed FAAH specifically in the CA1 field. The identification of anatomically related-neuronal substrates that expressed 2-AG/CB1 signaling system and selective CaBPs should be considered when analyzing the cannabinoid signaling associated with hippocampal functions.

Journal Article;

This work is supported by 7th Framework Programme of European Union [grant number HEALTH-F2-2008-223713, REPROBESITY]; Ministerio de Ciencia e Innovación [grant numbers SAF2010-19087, SAF 2010-20521]; Instituto de Salud Carlos III, Ministerio de Economía y Competitividad, UE-ERDF [grant number CP12/03109], Red de Trastornos Adictivos [grant numbers RD12/0028/0001, RD12/0028/0009], CIBERobn; Plan Nacional Sobre Drogas, Ministerio de Sanidad y Consumo [grant number PNSD2010/143]; Consejería de Economía, Innovación y Ciencia, Junta de Andalucía, UE/ERDF [grant number CTS-433, P-11-CVI-07637]; Consejería de Salud, Junta de Andalucía [grant numbers PI0232/2008, PI0029/2008, SAS111224]; Fundació La Marató de TV3 [grant number 386/C/2011]. Juan Suárez is recipient of a “Miguel Servet” research contract from the National System of Health (Instituto de Salud Carlos III, grant number CP12/03109).