An endocannabinoid system is present in the mouse olfactory epithelium but does not modulate olfaction. (6th August 2015) - Hutch, C.R.
Highlights: Mouse olfactory epithelium (OE) has CB1 receptors on: neurons, glia, and progenitor cells. 2-Arachidonylglycerol and its synthetic and degradation enzymes are present. CB1- and CB2-deficient mice have fewer progenitor cells and neurons in the OE. Loss of OE neurons in CB1- and CB2-deficient mice does not lead to olfaction deficits. Endocannabinoids do not modulate olfactory sensitivity in the mouse. Abstract: Endocannabinoids modulate a diverse array of functions including progenitor cell proliferation in the central nervous system, and odorant detection and food intake in the mammalian central olfactory system and larval Xenopus laevis peripheral olfactory system. However, the presence and role of endocannabinoids in the peripheral olfactory epithelium have not been examined in mammals. We found the presence of cannabinoid type 1 (CB1) and cannabinoid type 2 (CB2) receptor protein and mRNA in the olfactory epithelium. Using either immunohistochemistry or calcium imaging we localized CB1 receptors on neurons, glia-like sustentacular cells, microvillous cells and progenitor-like basal cells. To examine the role of endocannabinoids, CB1- and CB2- receptor-deficient (CB1 −/− /CB2 −/− ) mice were used. The endocannabinoid 2-arachidonylglycerol (2-AG) was present at high levels in both C57BL/6 wildtype and CB1 −/− /CB2 −/− mice. 2-AG synthetic and degradative enzymes are expressed in wildtype mice. A small but significant decrease in basal cell and olfactory sensory neuron numbers was observed in CB1 −/− /CB2 −/− mice compared to wildtype mice. The decrease in olfactory sensory neurons did not translate to impairment in olfactory-mediated behaviors assessed by the buried food test and habituation/dishabituation test. Collectively, these data indicate the presence of an endocannabinoid system in the mouse olfactory epithelium. However, unlike in tadpoles, endocannabinoids do not modulate olfaction. Further investigation on the role of endocannabinoids in progenitor cell function in the olfactory epithelium is warranted.