Nitric oxide and guanylate cyclase signalling are differentially involved in gonadotrophin (LH) release responses to two endogenous GnRHs from goldfish pituitary cells

Protective effect of curcumin on fertility in cyclophosphamide exposed rats: Involvement of multiple pathways

This study assesses the effect of curcumin on cyclophosphamide (CPA)-induced functional alterations of the testicular, brain, and pituitary axis in common rodents, rats. Only CPA was given at 150 mg/kg body weight only on Day 1 or orally pre and posttreated with curcumin at 20 mg/kg body weight successively for 14 days. The outcomes showed that curcumin pre and posttreatments significantly affected the elevation of biomarkers of oxidative stress in CPA-induced rats, moreover, it increased nonenzymatic antioxidant levels in the epididymis, testes, and brain of the treated rats used in this study. In addition, followed by the preservation of histo-architectures of the epididymis, testes, and brain in the rats treated with CPA, curcumin helped in increasing the sperm quality and quantity and suppressing both the inflammatory indices and the activities of caspase-3, while pretreatment with curcumin gave a better result than posttreatment with curcumin. This may, therefore, represent a prospective adjuvant against CPA-induced spermatogenic deficits in humans. PRACTICAL APPLICATIONS: Jointly, through the antiapoptotic, antioxidant, and anti-inflammatory activities of curcumin, it instigated the toxicity of CPA-induced to be modulated along the testicular, brain, and pituitary axis in the rats. This may, therefore, represent a prospective therapeutic adjuvant against CPA-induced spermatogenic deficits in humans.

Nitric Oxide and the Neuroendocrine Control of the Osmotic Stress Response in Teleosts

The involvement of nitric oxide (NO) in the modulation of teleost osmoresponsive circuits is suggested by the facts that NO synthase enzymes are expressed in the neurosecretory systems and may be regulated by osmotic stimuli. The present paper is an overview on the research suggesting a role for NO in the central modulation of hormone release in the hypothalamo-neurohypophysial and the caudal neurosecretory systems of teleosts during the osmotic stress response. Active NOS enzymes are constitutively expressed by the magnocellular and parvocellular hypophysiotropic neurons and the caudal neurosecretory neurons of teleosts. Moreover, their expression may be regulated in response to the osmotic challenge. Available data suggests that the regulatory role of NO appeared early during vertebrate phylogeny and the neuroendocrine modulation by NO is conservative. Nonetheless, NO seems to have opposite effects in fish compared to mammals. Indeed, NO exerts excitatory effects on the electrical activity of the caudal neurosecretory neurons, influencing the amount of peptides released from the urophysis, while it inhibits hormone release from the magnocellular neurons in mammals.

Comparative aspects of GnRH-Stimulated signal transduction in the vertebrate pituitary - Contributions from teleost model systems

Gonadotropin-releasing hormone (GnRH) is a major regulator of reproduction through actions on pituitary gonadotropin release and synthesis. Although it is often thought that pituitary cells are exposed to only one GnRH, multiple GnRH forms are delivered to the pituitary of teleost fishes; interestingly this can include the cGnRH-II form usually thought to be non-hypophysiotropic. GnRHs can regulate other pituitary cell-types, both directly as well as indirectly, and multiple GnRH receptors (GnRHRs) may also be expressed in the pituitary, and even within a single pituitary cell-type. Literature on the differential actions of native GnRH isoforms in primary pituitary cells is largely derived from teleost fishes. This review will outline the diversity and complexity of GnRH-GnRHR signal transduction found within vertebrate gonadotropes as well as extra-gonadotropic sites with special emphasis on comparative studies from fish models. The implications that GnRHR transduction mechanisms are GnRH isoform-, function-, and cell-specific are also discussed.

Chemoprotective role of quercetin in manganese-induced toxicity along the brain-pituitary-testicular axis in rats

Reproductive dysfunction in response to manganese exposure has been reported in humans and animals. Quercetin, a bioflavonoid widely distributed in fruits, vegetables and beverages has been shown to possess antioxidant, anti-inflammatory and anti-apoptotic activities in different experimental model systems. However, there is dearth of scientific information on the influence of quercetin on manganese-induced reproductive toxicity. This study was designed to evaluate the influence of quercetin on manganese-induced functional alterations along the brain-pituitary- testicular axis in rats. Manganese was administered alone at 15 mg/kg body weight or orally co-treated with quercetin at 10 and 20 mg/kg body weight for 45 consecutive days. Results indicated that quercetin co-treatment significantly (p < 0.05) inhibited manganese-induced elevation in biomarkers of oxidative stress whereas it increased antioxidant enzymes activities and glutathione level in the brain, testes and epididymis of the treated rats. Furthermore, quercetin mediated suppression of inflammatory indices and caspase-3 activity was accompanied by preservation of histo-architectures of the brain, testes and epididymis in manganese-treated rats. The significant reversal of manganese-induced decreases in reproductive hormones (i.e. luteinizing hormone, follicle-stimulating hormone and testosterone) and testicular activities of acid phosphatase, alkaline phosphatase and lactate dehydrogenase by quercetin was complemented by an increase in sperm quality and quantity in the treated rats. Collectively, quercetin modulated manganese-induced toxicity along the brain-pituitary-testicular axis in rats via its intrinsic antioxidant, anti-inflammatory and anti-apoptotic activities, and may thus represent a potential pharmacological agent against manganese-induced male reproductive deficits in humans.

Relationship between nitric oxide- and calcium-dependent signal transduction pathways in growth hormone release from dispersed goldfish pituitary cells

Nitric oxide (NO) and Ca(2+) are two of the many intracellular signal transduction pathways mediating the control of growth hormone (GH) secretion from somatotropes by neuroendocrine factors. We have previously shown that the NO donor sodium nitroprusside (SNP) elicits Ca(2+) signals in identified goldfish somatotropes. In this study, we examined the relationships between NO- and Ca(2+)-dependent signal transduction mechanisms in GH secretion from primary cultures of dispersed goldfish pituitary cells. Morphologically identified goldfish somatotropes stained positively for an NO-sensitive dye indicating they may be a source of NO production. In 2h static incubation experiments, GH release responses to the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) were attenuated by CoCl2, nifedipine, verapamil, TMB-8, BHQ, and KN62. In column perifusion experiments, the ability of SNP to induce GH release was impaired in the presence of TMB-8, BHQ, caffeine, and thapsigargin, but not ryanodine. Caffeine-elicited GH secretion was not affected by the NO scavenger PTIO. These results suggest that NO-stimulated GH release is dependent on extracellular Ca(2+) availability and voltage-sensitive Ca(2+) channels, as well as intracellular Ca(2+) store(s) that possess BHQ- and/or thapsigargin-inhibited sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases, as well as TMB-8- and/or caffeine-sensitive, but not ryanodine-sensitive, Ca(2+)-release channels. Calmodulin kinase-II also likely participates in NO-elicited GH secretion but caffeine-induced GH release is not upstream of NO production. These findings provide insights into how NO actions many integrate with Ca(2+)-dependent signalling mechanisms in goldfish somatotropes and how such interactions may participate in the GH-releasing actions of regulators that utilize both NO- and Ca(2+)-dependent transduction pathways.

PACAP modulates GnRH signaling in gonadotropes

Hypothalamic gonadotropin-releasing hormone is known to be critical for normal gonadotropin biosynthesis and secretion by the gonadotrope cells of the anterior pituitary gland. Additional regulation is provided by gonadal steroid feedback as well as by intrapituitary factors, such as activin and follistatin. Less well-appreciated is the role of pituitary adenylate-cyclase activating polypeptide (PACAP) as both a hypothalamic-pituitary releasing factor as well as an autocrine-paracrine factor within the pituitary. PACAP regulates gonadotropin expression alone and through modulation of GnRH responsiveness achieved by increases in GnRH receptor expression and interactions at the level of intracellular signaling pathways. In addition to direct effects on the gonadotrope, PACAP stimulates follistatin secretion by the folliculostellate cells and thereby contributes to differential expression of the gonadotropin subunits. Conversely, GnRH augments the ability of PACAP to regulate gonadotrope function by increasing pituitary PACAP and PACAP receptor expression. This review will summarize the current understanding of the mechanisms by which PACAP modulates gonadotrope function, with a focus on interactions with GnRH.

MEK1/2 differentially participates in GnRH actions on goldfish LH and GH secretion and hormone protein availability: acute and long-term effects, in vitro

Two endogenous gonadotropin-releasing hormones (GnRHs), sGnRH and cGnRH-II, stimulate LH and GH release via protein kinase C (PKC) signaling in goldfish. In this study, extracellular signal-regulated kinase kinase 1 and 2 (MEK1/2) involvement in acute and prolonged GnRH effects on goldfish gonadotrope and somatotrope functions, as well as potential interactions with PKC in the control of LH and GH release from goldfish pituitary cells was investigated. MEK1/2 inhibitors U0126 and PD098059 significantly decreased sGnRH but not cGnRH-II-stimulated GH release from perifused goldfish pituitary cells and U0126 significantly reduced the GH, but not the LH, release responses to synthetic PKC activators. In long-term static incubations (up to 24h) with goldfish pituitary cells, U0126 generally did not affect basal LH release but attenuated sGnRH- and cGnRH-II-induced LH release, as well as the time-dependent effects of sGnRH and/or cGnRH-II to elevate total LH availability (sum of release and cell content). sGnRH and cGnRH-II reduced cellular GH content and/or total GH availability at 2, 6, and 12h while static incubation with U0126 alone generally increased basal GH release but reduced cellular GH content and/or the total amount of GH available. U0126 also selectively reduced the sGnRH-induced GH release responses at 6 and 24h but paradoxically inhibited cGnRH-II-stimulated GH secretion while enhancing sGnRH-elicited GH release at 2h. Taken together, this study reveals the complexity of GnRH-stimulated MEK1/2 signaling and adds to our understanding of cell-type- and GnRH-isoform-selective signal transduction in the regulation of pituitary cell hormone release and production.

Expression of kisspeptins and kiss receptors suggests a large range of functions for kisspeptin systems in the brain of the European sea bass

This study, conducted in the brain of a perciform fish, the European sea bass, aimed at raising antibodies against the precursor of the kisspeptins in order to map the kiss systems and to correlate the expression of kisspeptins, kiss1 and kiss2, with that of kisspeptin receptors (kiss-R1 and kiss-R2). Specific antibodies could be raised against the preprokiss2, but not the preoprokiss1. The data indicate that kiss2 neurons are mainly located in the hypothalamus and project widely to the subpallium and pallium, the preoptic region, the thalamus, the pretectal area, the optic tectum, the torus semicircularis, the mediobasal medial and caudal hypothalamus, and the neurohypophysis. These results were compared to the expression of kiss-R1 and kiss-R2 messengers, indicating a very good correlation between the wide distribution of Kiss2-positive fibers and that of kiss-R2 expressing cells. The expression of kiss-R1 messengers was more limited to the habenula, the ventral telencephalon and the proximal pars distalis of the pituitary. Attempts to characterize the phenotype of the numerous cells expressing kiss-R2 showed that neurons expressing tyrosine hydroxylase, neuropeptide Y and neuronal nitric oxide synthase are targets for kisspeptins, while GnRH1 neurons did not appear to express kiss-R1 or kiss-R2 messengers. In addition, a striking result was that all somatostatin-positive neurons expressed-kissR2. These data show that kisspeptins are likely to regulate a wide range of neuronal systems in the brain of teleosts.

Nitric oxide signaling in ghrelin-induced LH release from goldfish pituitary cells

Among its many known functions, ghrelin has been proposed to participate in the regulation of reproduction; however, its effect on pituitary LH release is controversial, especially in mammals. In the goldfish, ghrelin directly stimulates pituitary LH release via increased entry of calcium through voltage sensitive channels and activation of protein kinase C. Nitric oxide (NO) is an important signaling molecule in many physiological systems including hormone regulation at the level of the pituitary. Goldfish pituitary cells and extracts have previously been reported to express immunoreactivity for inducible and neuronal NO synthase (iNOS and nNOS). In this study, we determined if NO is involved in goldfish ghrelin (gGRLN(19))-induced LH release from primary cultures of dispersed goldfish pituitary cells in column perifusion. Treatment with the NO scavenger PTIO significantly decreased gGRLN(19)-induced LH release and co-treatment with the NO donor SNP and gGRLN(19) did not induce an additive increase in LH release, suggesting that NO is critical to gGRLN(19) stimulation of LH release in goldfish pituitary cells. Further work examined the involvement of the NOS using the NOS isoform-selective inhibitors 1400W, 7-Ni, and AGH. While 1400W (selective for iNOS) and AGH (selective for iNOS and nNOS) abolished gGRLN(19)-induced LH release from goldfish pituitary cells, 7-Ni (selective for nNOS and endothelial NOS) had no significant effect on this stimulation. Our results indicate, for the first time in a teleost species, that gGRLN(19)-induced LH release from pituitary cells is NO-dependent and likely involves iNOS, adding to the understanding of GRLN intracellular signaling in general and specifically to the regulation of LH release from the pituitary.