Anandamide modulates the expression of GnRH-II and GnRHRs in frog, Rana esculenta, diencephalon

Abstract

In the hypothalamus, endocannabinoids affect neuroendocrine activity by means of Gonadotropin-Releasing-Hormone-I (GnRH-I) inhibition. Since most vertebrates, human included, possess at least two GnRH molecular forms, the aim of this work was to investigate the effect of endocannabinoids on GnRH molecular forms other than GnRH-I and on GnRHRs.Thus, we cloned GnRH precursors as well as GnRH receptors (GnRHR-I, GnRHR-II, GnRHR-III) from the diencephalons of the anuran amphibian, Rana esculenta. GnRH-II expression was evaluated in pituitary, whole brain, spinal cord, hindbrain, midbrain and forebrain during the annual sexual cycle. Then, in post-reproductive period (May), GnRH-I, GnRH-II and GnRHRs expression was evaluated by quantitative real time (qPCR) after incubation of diencephalons with the endocannabinoid anandamide (AEA). AEA significantly decreased GnRH-I and GnRH-II expression, up regulated GnRHR-I and GnRHR-II mRNA and it had no effect upon GnRHR-III expression. These effects were counteracted by SR141716A (Rimonabant), a selective antagonist of type I cannabinoid receptor (CB1).In conclusion our results demonstrate a CB1 receptor dependent modulation of GnRH system expression rate (both ligands and receptors) in frog diencephalons. In particular, we show that AEA, besides GnRH-I, also acts on GnRH-II expression.