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

Differential gene expression and gut microbiota composition in low-altitude and high-altitude goats

Previous studies have presented evidence suggesting that altitude exerts detrimental effects on reproductive processes, yet the underlying mechanism remains elusive. Our study employed two distinct goat breeds inhabiting low and high altitudes, and conducted a comparative analysis of mRNA profiles in testis tissues and the composition of gut microbiota. The results revealed a reduced testis size in high-altitude goats. RNA-seq analysis identified the presence of 214 differentially expressed genes (DEGs) in the testis. These DEGs resulted in a weakened immunosuppressive effect, ultimately impairing spermatogenesis in high-altitude goats. Additionally, 16S rDNA amplicon sequencing recognized statistically significant variations in the abundance of the genera Treponema, unidentified_Oscillospiraceae, Desulfovibrio, Butyricicoccus, Dorea, Parabacteroides between the two groups. The collective evidence demonstrated the gut and testis played a synergistic role in causing decreased fertility at high altitudes. Our research provides a theoretical basis for future investigations into the reproductive fitness of male goats.

Effect of central administration of indomethacin on anandamide-induced GnRH/LH secretion in the hypothalamus of anoestrous ewes

Introduction

It is suggested that cannabinoids (CBs) may disturb reproduction through action on hypothalamic gonadotropin-releasing hormone (GnRH) neurons directly or indirectly through intermediates such as prostaglandins. The study aimed to determine the influence of intracerebroventricular (i.c.v.) injection of the endogenous cannabinoid anandamide (N-arachidonoylethanolamine - AEA), alone or with the prostaglandin synthesis inhibitor indomethacin (IND), on GnRH/luteinising hormone (LH) secretion. The purpose of the research was to clarify the role of endocannabinoids and their interaction with prostaglandins in the regulation of reproduction at the level of the hypothalamus and pituitary in anoestrous sheep.

Material and Methods

The study was performed on 24 anoestrous ewes divided into four experimental groups: a control group receiving i.c.v. injection of Ringer-Locke solution, an AEA group that received i.c.v. injection of 30 μM of AEA, an IND group receiving i.c.v. injection of 5 μM of IND and an AEA + IND group that received i.c.v. injections of 30 μM of AEA and 5 μM of IND.

Results

Anandamide stimulated GnRH protein and gene expression in the median eminence and protein expression in the preoptic area without influencing GnRH messenger RNA (mRNA) in this structure. Indomethacin reversed the changes in GnRH secretion after AEA administration. It was also found that AEA stimulated LH mRNA in the pituitary without influencing LH release.

Conclusion

Our results support the role of endogenous cannabinoids in the regulation of reproductive processes at the central nervous system level. They may act directly on the hypothalamic GnRH neurons or indirectly through intermediates such as prostaglandins.

Diverse role of endocannabinoid system in mammalian male reproduction

Endocannabinoid system (ECS) is known for its modulatory role in numerous physiological processes in the body. Endocannabinoids (eCBs) are endogenous lipid molecules which function both centrally and peripherally. The ECS is best studied in the central nervous system (CNS), immune system as well as in the metabolic system. The role of ECS in male reproductive system is emerging and the presence of a complete enzymatic machinery to synthesize and metabolize eCBs has been demonstrated in male reproductive tract. Endocannabinoid concentrations and alterations in their levels have been reported to affect the functioning of spermatozoa. A dysfunctional ECS has also been linked to the development of prostate cancer, the leading cause of cancer related mortality among male population. This review is an attempt to provide an insight into the significant role of endocannabinoids in male reproduction and further summarize recent findings that demonstrate the manner in which the endocannabinoid system impacts male sexual behavior and fertility.

The Complex Interplay between Endocannabinoid System and the Estrogen System in Central Nervous System and Periphery

The endocannabinoid system (ECS) is a lipid cell signaling system involved in the physiology and homeostasis of the brain and peripheral tissues. Synaptic plasticity, neuroendocrine functions, reproduction, and immune response among others all require the activity of functional ECS, with the onset of disease in case of ECS impairment. Estrogens, classically considered as female steroid hormones, regulate growth, differentiation, and many other functions in a broad range of target tissues and both sexes through the activation of nuclear and membrane estrogen receptors (ERs), which leads to genomic and non-genomic cell responses. Since ECS function overlaps or integrates with many other cell signaling systems, this review aims at updating the knowledge about the possible crosstalk between ECS and estrogen system (ES) at both central and peripheral level, with focuses on the central nervous system, reproduction, and cancer.

Kisspeptins, new local modulators of male reproduction: A comparative overview

Spermatogenesis is a complex process that leads to the production of male gametes within the testis through the coordination of mitotic, meiotic and differentiation events, under a deep control of endocrine, paracrine and autocrine modulators along the Hypothalamus-pituitary-gonad (HPG) axis. The kisspeptin system plays a fundamental role along the HPG axis as it is the main positive modulator upstream of the hypothalamic neurons that secrete the Gonadotropin Releasing Hormone (GnRH), the decapeptide that supports pituitary gonadotropins and the production of gonadal sex steroid. Currently, kisspeptins and their receptor, KISS1R, have a recognized activity in the central control of puberty onset, sex maturation, reproduction and sex-steroid feedback mechanisms in both animal models and human. However, kisspeptin signaling has been widely reported in peripheral tissues, particularly in the testis of mammalian and non-mammalian vertebrates, with functions related to Leydig cells physiology and steroid biosynthesis, spermatogenesis progression and spermatozoa functions, but its mandatory role within the testis is still a matter of discussion. This review provides a summary of the main intratesticular effects of kisspeptin in vertebrates, via a comparative approach. Particular emphasis was devoted to data from the anuran amphibian Pelophylax esculentus, the first animal model in which the direct intratesticular activity of kisspeptin was reported.

Celebrating 50+ years of research on the reproductive biology and endocrinology of the green frog: An overview

This issue is dedicated to the late Professor Giovanni Chieffi, and this article is an overview of the research on Comparative Endocrinology of reproduction using Rana esculenta (alias Pelophylax esculentus) as a model system. Starting from the early 1970s till today, a large quantity of work have been conducted both in the fields of experimental endocrinology and in the definition of the diffuse neuroendocrine system, with a major focus on the increasing role of regulatory peptides. The various aspects investigated concerned the histological descriptions of principal endocrine glands of the hypothalamic-pituitary-gonadal (HPG) axis, the localization and distribution in the HPG of several different substances (i.e. neurosteroids, hypothalamic peptide hormones, pituitary gonadotropins, gonadal sex steroids, and other molecules), the determination of sex hormone concentrations in both serum and tissues, the hormone manipulations, as well as the gene and protein expression of steroidogenic enzymes and their respective receptors. All together these researches, often conducted considering different periods of the annual reproductive cycle of the green frog, allowed to understand the mechanism of cascade control/regulation of the HPG axis of R. esculenta, characterizing the role of different hormones in the two sexes, and testing the hypotheses about the function of single hormones in different target organs. It becomes evident from the review that, in their simplest form, several features of this species are specular as compared to those of other vertebrate species and that reproduction in this frog species is either under endogenous multi-hormonal control or by a wide array of different factors. Our excursus of this research, spanning almost five decades, shows that R. esculenta has been intensively and successfully used as an animal model in reproductive endocrinology as well as several field studies such as those involving environmental concerns that focus on the effects of endocrine disruptors and other environmental contaminants.

The Influence of Anandamide on the Anterior Pituitary Hormone Secretion in Ewes-Ex Vivo Study

Cannabinoids (CBs) are involved in the neuroendocrine control of reproductive processes by affecting GnRH and gonadotropins secretion. The presence of cannabinoid receptors (CBR) in the pituitary raises a presumption that anandamide (AEA), the endogenous cannabinoid, may act on gonadotrophic hormones secretion directly at the level of the anterior pituitary (AP). Thus, the aim of the study was to investigate the influence of AEA on gonadotropins secretions from AP explants taken from anestrous ewes. It was demonstrated that AEA inhibited GnRH stimulated luteinizing hormone (LH) and follicle stimulating hormone (FSH) secretion from the AP explants. Anandamide influences both LH and FSH gene expressions as well as their release. AEA also affected gonadoliberin receptor (GnRHR) synthesis and expression. The presence of CB1R transcript in AP explants were also demonstrated. It could be suggested that some known negative effects of cannabinoids on the hypothalamic-pituitary-gonadal axis activity may be caused by the direct action of these compounds at the pituitary level.

Impact of Dietary Fats on Brain Functions

BACKGROUND

Adequate dietary intake and nutritional status have important effects on brain functions and on brain health. Energy intake and specific nutrients excess or deficiency from diet differently affect cognitive processes, emotions, behaviour, neuroendocrine functions and synaptic plasticity with possible protective or detrimental effects on neuronal physiology. Lipids, in particular, play structural and functional roles in neurons. Here the importance of dietary fats and the need to understand the brain mechanisms activated by peripheral and central metabolic sensors. Thus, the manipulation of lifestyle factors such as dietary interventions may represent a successful therapeutic approach to maintain and preserve brain health along lifespan.

METHODS

This review aims at summarizing the impact of dietary fats on brain functions.

RESULTS

Starting from fat consumption, nutrient sensing and food-related reward, the impact of gut-brain communications will be discussed in brain health and disease. A specific focus will be on the impact of fats on the molecular pathways within the hypothalamus involved in the control of reproduction via the expression and the release of Gonadotropin-Releasing Hormone. Lastly, the effects of specific lipid classes such as polyunsaturated fatty acids and of the "fattest" of all diets, commonly known as "ketogenic diets", on brain functions will also be discussed.

CONCLUSION

Despite the knowledge of the molecular mechanisms is still a work in progress, the clinical relevance of the manipulation of dietary fats is well acknowledged and such manipulations are in fact currently in use for the treatment of brain diseases.

Kisspeptin regulates steroidogenesis and spermiation in anuran amphibian

Kisspeptin (Kp) system has a recognized role in the control of gonadotropic axis, at multiple levels. Recently, a major focus of research has been to assess any direct activity of this system on testis physiology. Using the amphibian anuran, Pelophylax esculentus, as animal model, we demonstrate - for the first time in non-mammalian vertebrate - that testis expresses both Kiss-1 and Gpr54 proteins during the annual sexual cycle and that ex vivo 17B-estradiol (E₂, 10^-6 M) increases both proteins over control group. Since the interstitium is the main site of localization of both ligand and receptor, its possible involvement in the regulation of steroidogenesis has been evaluated by ex vivo treatment of testis pieces with increasing doses of Kp-10 (10^-9-10^-6 M). Treatments have been carried out in February - when a new wave of spermatogenesis occurs - and affect the expression of key enzymes of steroidogenesis inducing opposite effects on testosterone and estradiol intratesticular levels. Morphological analysis of Kp-treated testes reveals higher number of tubules with spermatozoa detached from Sertoli cells than control group and the expression of connexin 43, the main junctional protein in testis, is deeply affected by the treatment. In spite of the effects on spermatozoa observed ex vivo, in vivo administration of Kp-10 has been unable to induce sperm release in cloacal fluid. In conclusion, we demonstrate Kp-10 effects on steroidogenesis with possible involvement in the balance between testosterone and estradiol levels, and report new Kp-10 activities on spermatozoa-Sertoli cell interaction.

Role of the endocannabinoid system in vertebrates: Emphasis on the zebrafish model

The endocannabinoid system (eCBs), named after the plant Cannabis sativa, comprises cannabinoid receptors, endogenous ligands known as "endocannabinoids", and enzymes involved in the biosynthesis and degradation of these ligands, as well as putative transporters for these ligands. ECBs proteins and small molecules have been detected in early embryonic stages of many vertebrate models. As a result, cannabinoid receptors and endogenous as well as exogenous cannabinoids influence development and behavior in many vertebrate species. Understanding the precise mechanisms of action for the eCBs will provide an invaluable guide towards elucidation of vertebrate development and will also help delineate how developmental exposure to marijuana might impact health and cognitive/executive functioning in adulthood. Here we review the developmental roles of the eCBs in vertebrates, focusing our attention on the zebrafish model. Since little is known regarding the eCBs in zebrafish, we provide new data on the expression profiles of eCBs genes during development and in adult tissue types of this model organism. We also highlight exciting areas for future investigations, including the synaptic regulation of eCBs, its role in reward and addiction, and in nervous system development and plasticity.

Effects of Neuroendocrine CB1 Activity on Adult Leydig Cells

Endocannabinoids control male reproduction acting at central and local level via cannabinoid receptors. The cannabinoid receptor CB1 has been characterized in the testis, in somatic and germ cells of mammalian and non-mammalian animal models, and its activity related to Leydig cell differentiation, steroidogenesis, spermiogenesis, sperm quality, and maturation. In this short review, we provide a summary of the insights concerning neuroendocrine CB1 activity in male reproduction focusing on adult Leydig cell ontogenesis and steroid biosynthesis.

Anandamide acts via kisspeptin in the regulation of testicular activity of the frog, Pelophylax esculentus

In the frog Pelophylax esculentus, the endocannabinoid anandamide (AEA) modulates Gonadotropin Releasing Hormone (GnRH) system in vitro and down-regulates steroidogenic enzymes in vivo. Thus, male frogs were injected with AEA ± SR141716A, a cannabinoid receptor 1 (CB1) antagonist, to evaluate possible effects on GnRH and Kiss1/Gpr54 systems, gonadotropin receptors and steroid levels. In frog diencephalons, AEA negatively affected both GnRH and Kiss1/Gpr54 systems. In testis, AEA induced the expression of gonadotropin receptors, cb1, gnrh2 and gnrhr3 meanwhile reducing gnrhr2 mRNA and Kiss1/Gpr54 proteins. Furthermore, aromatase (Cyp19) expression increased in parallel to testosterone decrease and estradiol increase. In vitro treatment of testis with AEA revealed direct effects on Cyp19 and induced the expression of the AEA-degrading enzyme Faah. Lastly, AEA effects on Faah were counteracted by the antiestrogen ICI182780, indicating estradiol mediated effect. In conclusion, for the first time we show in a vertebrate that AEA regulates testicular activity through kisspeptin system.

Kisspeptin drives germ cell progression in the anuran amphibian Pelophylax esculentus: a study carried out in ex vivo testes

Kisspeptin, via Gpr54 receptor, regulates puberty onset in most vertebrates. Thus, the direct involvement of kisspeptin activity in testis physiology was investigated in the anuran amphibian, Pelophylax esculentus. In this vertebrate gpr54 mRNA has been localized in both interstitial compartment and spermatogonia (SPG), whereas SPG proliferation requires the cooperation between estradiol and testicular Gonadotropin releasing hormone (Gnrh). In the pre-reproductive period, dose response curve to assess the effects of Kisspeptin-10 (Kp-10) was carried out in vitro (dose range: 10(-9)-10(-6)M; incubation times: 1 and 4h); proliferative activity and germ cell progression were evaluated by expression analysis of proliferating cell nuclear antigen (pcna), estrogen receptor beta (erβ), Gnrh system (gnrh1, gnrh2, gnrhr1, r2, r3) and by the count of empty, mitotic and meiotic tubules. All selected markers were up regulated at 4h Kp-10 incubation. Histological analysis also proved the increase of mitotic activity and the progression of spermatogenesis. Besides Kp-10 modulation of testicular Gnrh system, in vitro treatment with 17β-estradiol (10(-6)M) ± the antagonist ICI182-780 (10(-5)M) revealed gnrh2 and gnrhr3 estrogen dependent expression. In the reproductive period, testes were incubated for 1 and 4h with Kp-10 (10(-7)M) or Kp-10 (10(-7)M)+kisspeptin antagonist [Kp-234 (10(-6)M)]. Results obtained in the pre-reproductive period were confirmed and Kp-234 completely counteracted Kp-10 effects. In conclusion, Kp-10 modulated the expression of pcna, erβ, gnrhs and gnrhrs, inducing the progression of the spermatogenesis.

Expression analysis of gnrh1 and gnrhr1 in spermatogenic cells of rat

Hypothalamic Gonadotropin Releasing Hormone (GnRH), via GnRH receptor (GnRHR), is the main actor in the control of reproduction, in that it induces the biosynthesis and the release of pituitary gonadotropins, which in turn promote steroidogenesis and gametogenesis in both sexes. Extrabrain functions of GnRH have been extensively described in the past decades and, in males, local GnRH activity promotes the progression of spermatogenesis and sperm functions at several levels. The canonical localization of Gnrh1 and Gnrhr1 mRNA is Sertoli and Leydig cells, respectively, but ligand and receptor are also expressed in germ cells. Here, we analysed the expression rate of Gnrh1 and Gnrhr1 in rat testis (180 days old) by quantitative real-time PCR (qPCR) and by in situ hybridization we localized Gnrh1 and Gnrhr1 mRNA in different spermatogenic cells of adult animals. Our data confirm the testicular expression of Gnrh1 and of Gnrhr1 in somatic cells and provide evidence that their expression in the germinal compartment is restricted to haploid cells. In addition, not only Sertoli cells connected to spermatids in the last steps of maturation but also Leydig and peritubular myoid cells express Gnrh1.

Hypothalamus-pituitary axis: an obligatory target for endocannabinoids to inhibit steroidogenesis in frog testis

Endocannabinoids - primarily anandamide (AEA) and 2-arachidonoylglycerol (2-AG) - are lipophilic molecules that bind to cannabinoid receptors (CB1 and CB2). They affect neuroendocrine activity inhibiting gonadotropin releasing hormone (GnRH) secretion and testosterone production in rodents, through a molecular mechanism supposed to be hypothalamus dependent. In order to investigate such a role, we choose the seasonal breeder, the anuran amphibian Rana esculenta, an experimental model in which components of the endocannabinoid system have been characterized. In February, at the onset of a new spermatogenetic wave, we carried out in vitro incubations of frog testis with AEA, at 10(-9)M dose. Such a treatment had no effect on the expression of cytochrome P450 17alpha hydroxylase/17,20 lyase (cyp17) nor 3-β-hydroxysteroid dehydrogenase/Δ-5-4 isomerase (3β-HSD), key enzymes of steroidogenesis. To understand whether or not the functionality of the hypothalamus-pituitary axis could be essential to support the role of endocannabinoids in steroidogenesis, frogs were injected with AEA, at 10(-8)M dose. Differently from in vitro experiment, the in vivo administration of AEA reduced the expression of cyp17 and 3β-HSD. Whereas the effect on 3β-HSD was counteracted by SR141716A (Rimonabant) - a selective antagonist of CB1, thus indicating a CB1 dependent modulation - the effect on cyp17 was not, suggesting a possible involvement of receptors other than CB1, probably the type-1 vanilloid receptor (TRPV1), since AEA works as an endocannabinoid and an endovanilloid as well. In conclusion our results indicate that endocannabinoids, via CB1, inhibit the expression of 3β-HSD in frog testis travelling along the hypothalamus-pituitary axis.

Endocannabinoids are Involved in Male Vertebrate Reproduction: Regulatory Mechanisms at Central and Gonadal Level

Endocannabinoids (eCBs) are natural lipids regulating a large array of physiological functions and behaviors in vertebrates. The eCB system is highly conserved in evolution and comprises several specific receptors (type-1 and type-2 cannabinoid receptors), their endogenous ligands (e.g., anandamide and 2-arachidonoylglycerol), and a number of biosynthetic and degradative enzymes. In the last few years, eCBs have been described as critical signals in the control of male and female reproduction at multiple levels: centrally, by targeting hypothalamic gonadotropin-releasing-hormone-secreting neurons and pituitary, and locally, with direct effects on the gonads. These functions are supported by the extensive localization of cannabinoid receptors and eCB metabolic enzymes at different levels of the hypothalamic-pituitary-gonadal axis in mammals, as well as bonyfish and amphibians. In vivo and in vitro studies indicate that eCBs centrally regulate gonadal functions by modulating the gonadotropin-releasing hormone-gonadotropin-steroid network through direct and indirect mechanisms. Several proofs of local eCB regulation have been found in the testis and male genital tracts, since eCBs control Sertoli and Leydig cells activity, germ cell progression, as well as the acquisition of sperm functions. A comparative approach usually is a key step in the study of physiological events leading to the building of a general model. Thus, in this review, we summarize the action of eCBs at different levels of the male reproductive axis, with special emphasis, where appropriate, on data from non-mammalian vertebrates.

Intra-testicular signals regulate germ cell progression and production of qualitatively mature spermatozoa in vertebrates

Spermatogenesis, a highly conserved process in vertebrates, is mainly under the hypothalamic-pituitary control, being regulated by the secretion of pituitary gonadotropins, follicle stimulating hormone, and luteinizing hormone, in response to stimulation exerted by gonadotropin releasing hormone from hypothalamic neurons. At testicular level, gonadotropins bind specific receptors located on the somatic cells regulating the production of steroids and factors necessary to ensure a correct spermatogenesis. Indeed, besides the endocrine route, a complex network of cell-to-cell communications regulates germ cell progression, and a combination of endocrine and intra-gonadal signals sustains the production of high quality mature spermatozoa. In this review, we focus on the recent advances in the area of the intra-gonadal signals supporting sperm development.

Updates in reproduction coming from the endocannabinoid system

The endocannabinoid system (ECS) is an evolutionarily conserved master system deeply involved in the central and local control of reproductive functions in both sexes. The tone of these lipid mediators-deeply modulated by the activity of biosynthetic and hydrolyzing machineries-regulates reproductive functions from gonadotropin discharge and steroid biosynthesis to the formation of high quality gametes and successful pregnancy. This review provides an overview on ECS and reproduction and focuses on the insights in the regulation of endocannabinoid production by steroids, in the regulation of male reproductive activity, and in placentation and parturition. Taken all together, evidences emerge that the activity of the ECS is crucial for procreation and may represent a target for the therapeutic exploitation of infertility.

Kisspeptin receptor, GPR54, as a candidate for the regulation of testicular activity in the frog Rana esculenta

Kisspeptins, acting via GPR54, are new players in the control of reproductive axis. They have the ability to communicate with GnRH neurons sending environmental, metabolic, and gonadal signals, with the induction of GnRH and LH secretion as final effect. At present, the physiological significance of kisspeptin signaling in the gonad is poorly investigated. We cloned GPR54 receptor from the anuran amphibian Rana esculenta testis and investigated its expression in several tissues (brain, spinal cord, ovary, muscle, and kidney). In particular, the expression analysis was carried out in pituitary and testis during the annual sexual cycle. Pituitary and testicular GPR54 mRNA increased at the end of the winter stasis (February) and reached high levels during the breeding season (April). The analysis of GPR54 expression in testis was reinforced by in situ hybridization that revealed GPR54 presence in the interstitial compartment and in proliferating germ cells. Testicular GPR54 expression in February and in June was indicated to be estradiol dependent. Furthermore, in February, kisspeptin-10 (Kp-10) induced the testicular expression of both GPR54 and estrogen receptor alpha (ERalpha) in a dose-dependent manner. Conversely, in March, Kp-10 had a biphasic effect on the expression of ERalpha, being inhibitory at short (1 h) and stimulatory at longer (4 h) incubation time. In conclusion, our results demonstrate that frog testis expresses GPR54 in an estradiol-dependent manner and that Kp-10 modulates the testicular expression of ERalpha; thus, the kisspeptin/GPR54 system might be locally involved in the regulation of estrogen-dependent testicular functions such as germ cell proliferation and steroidogenesis.

Role of the endocannabinoid system in the central regulation of nonmammalian vertebrate reproduction

The endocannabinoid system (ECS) has a well-documented pivotal role in the control of mammalian reproductive functions, by acting at multiple levels, that is, central (CNS) and local (gonads) levels. Since studies performed in animal models other than mammals might provide further insight into the biology of these signalling molecules, in the present paper we review the comparative data pointing toward the endocannabinoid involvement in the reproductive control of non-mammalian vertebrates, focussing in particular on the central regulation of teleost and amphibian reproduction. The morphofunctional distribution of brain cannabinoid receptors will be discussed in relation to other crucial signalling molecules involved in the control of reproductive functions, such as GnRH, dopamine, aromatase, and pituitary gonadotropins.

Endocannabinoids and endovanilloids: a possible balance in the regulation of the testicular GnRH signalling

Reproductive functions are regulated both at central (brain) and gonadal levels. In this respect, the endocannabinoid system (eCS) has a very influential role. Interestingly, the characterization of eCS has taken many advantages from the usage of animal models different from mammals. Therefore, this review is oriented to summarize the main pieces of evidence regarding eCS coming from the anuran amphibian Rana esculenta, with particular interest to the morphofunctional relationship between eCS and gonadotropin releasing hormone (GnRH). Furthermore, a novel role for endovanilloids in the regulation of a testicular GnRH system will be also discussed.

Anandamide regulates the expression of GnRH1, GnRH2, and GnRH-Rs in frog testis

Gonadotropin-releasing hormone (either GnRH1 or GnRH2) exerts a local activity in vertebrate testis, including human testis. Relationships between endocannabinoid (eCB) and GnRH systems in gonads have never been elucidated in any species so far. To reveal a cross-talk between eCBs and GnRH at testicular level, we characterized the expression of GnRH (GnRH1 and GnRH2) as well as GnRH receptor (GnRH-R1, -R2, and -R3) mRNA in the testis of the anuran amphibian Rana esculenta during the annual sexual cycle; furthermore, the corresponding transcripts were localized inside the testis by in situ hybridization. The possible endogenous production of the eCB, anandamide (AEA), was investigated in testis by analyzing the expression of its biosynthetic enzyme, Nape-pld. Incubations of testis pieces with AEA were carried out in the postreproductive period (June) and in February, when a new spermatogenetic wave takes place. In June, AEA treatment significantly decreased GnRH1 and GnRH-R2 mRNA, stimulated the transcription of GnRH2 and GnRH-R1, and did not affect GnRH-R3 expression. In February, AEA treatment upregulated GnRH2 and GnRH-R3 mRNA, downregulated GnRH-R2, and did not affect GnRH1 and GnRH-R1 expression. These effects were mediated by type 1 cannabinoid receptor (CB1) since they were fully counteracted by SR141716A (Rimonabant), a selective CB1 antagonist. In conclusion, eCB system modulates GnRH activity in frog testis during the annual sexual cycle in a stage-dependent fashion.