CONICET | Buscador de Institutos y Recursos Humanos

It is known that ∆9-tetrahydrocannabinol modulates autonomic neurotransmission. Therefore, we hypothesized that the central endocannabinoid system would also modulate salivary secretion by acting on the autonomic nervous system. Several studies suggest that the lateral preoptic-hypothalamic region is an important center for eliciting salivary secretion through pre-ganglionic parasympathetic nerves that project to the salivary glands in the rat. Moreover, in this study we found by immunohistochemical techniques that type 1 cannabinoid receptors (CB1-r) are densely distributed in the lateral hypothalamic area of adult male Wistar rats, supporting the hypothesis of autonomic modulation by the endocannabinoid system. In addition, we observed that the endocannabinoid anandamide (AEA, 50 ng/5ml vehicle) injected into the lateral cerebral ventricle (i.c.v) reduced significantly the salivary secretion induced by increasing doses of metacholine injected i.v. This inhibitory effect was partially but significantly blocked by previous i.c.v injection of the CB1-r antagonist, AM251 (500 ng/5ml vehicle), and totally blocked by previous injection of bicuculline (25 ng/5ml saline), a GABAA receptor antagonist. The i.c.v injection of saline or vehicle had no effect on salivary secretion. These results suggest that AEA inhibits saliva secretion by increasing GABAergic activity that inhibits the parasympathetic neurotransmission, since when the rats were decentralized by cutting the chorda tympani nerve, AEA injection was without effect. Moreover, the parasympathetic decentralization per se caused an inhibition of saliva secretion equivalent to that produced by AEA. On the contrary, when the superior cervical ganglion, a sympathetic ganglion, was removed, the inhibitory effect of AEA injection remained unaltered.