Interplay between the Endocannabinoid System and GnRH-I in the Forebrain of the Anuran Amphibian Rana esculenta

Abstract

The morphofunctional relationship between the endocannabinoid system and GnRH activity in the regulation of reproduction has poorly been investigated in vertebrates. Due to the anatomical features of lower vertebrate brain, in the present paper, we chose the frog Rana esculenta (anuran amphibian) as a suitable model to better investigate such aspects of the reproductive physiology. By using double-labeling immunofluorescence aided with a laser-scanning confocal microscope, we found a subpopulation of the frog hypothalamic GnRH neurons endowed with CB1 cannabinoid receptors. By means of semiquantitative RT-PCR assay, we have shown that, during the annual sexual cycle, GnRH-I mRNA (formerly known as mammalian GnRH) and CB1 mRNA have opposite expression profiles in the brain. In particular, this occurs in telencephalon and diencephalon, the areas mainly involved in GnRH release and control of the reproduction. Furthermore, we found that the endocannabinoid anandamide is able to inhibit GnRH-I mRNA synthesis; buserelin (a GnRH agonist), in turn, inhibits the synthesis of GnRH-I mRNA and induces an increase of CB1 transcription. Our observations point out the occurrence of a morphofunctional anatomical basis to explain a reciprocal relationship between the endocannabinoid system and GnRH neuronal activity.

Low 17beta-Estradiol Levels in Cnr1 Knock-Out Mice Affect Spermatid Chromatin Remodeling by Interfering with Chromatin Reorganization

“…In male, they act, directly and/or indirectly, at both central (hypothalamus and hypophysis) [16][17][18] and local levels (testis, epididymis and deferent ducts) via their cognate receptors [19][20][21][22][23][24][25][26]. At a central level, CNR1 regulates GnRH synthesis and release in frogs and rats, respectively [17,27].…”

Endocannabinoids and Kisspeptins: Two Modulators in Fight for the Regulation of GnRH Activity

“…A CB1 mediated self modulation of GnRH secreting neurons emerged in the anuran amphibian Rana esculenta . In male frogs, GnRH1 and CB1 share the localization inside the basal telencephalon and septum Meccariello et al, 2008); most GnRH1 secreting neurons are close to CB1 expressing neurons whereas a subpopulation of GnRH1 secreting neurons -in the approximate order of 20% -coexpresses CB1 . Such a neuroanatomical observation finds a possible functional explanation at molecular level.…”

“…Current opinion postulates that ECB mediated LH, but not FSH, inhibition is the result of hypothalamic ECB activity. In fact, ECBs are well known inhibitors of GnRH release (Scorticati et al, 2004) and GnRH transcription (Chianese et al, 2011b;Meccariello et al, 2008). By contrast, direct or indirect action of ECBs upon GnRH secreting neurons is still controversial and under investigation.…”

“…In both amphibians and teleost fish, CB1 was detected in the forebrain, the encephalic macro-area containing the anterior preoptic area, the encephalic region mainly involved in GnRH activity and in the control of gonadotropin discharge (Cottone et al, 2003Lam et al, 2006;Migliarini et al, 2006;Meccariello et al, 2008;Valenti et al, 2005). Besides an involvement in food intake, also in lower vertebrates ECS negatively modulates neuroendocrine machinery and reproduction.…”

“…Such a neuroanatomical observation finds a possible functional explanation at molecular level. In fact, mRNA and protein profiles of CB1 and GnRH1 are opposite in frog diencephalon during the annual sexual cycle Meccariello et al, 2008). Treatments of male diencephalons with buserelin, a long acting GnRH analogue, inhibit GnRH1 transcription and upregulate CB1 transcription; conversely, AEA treatments downregulate GnRH1 expression.…”