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To test the hypothesis that the hypothalmic gonadotropin-releasing hormone (GnRH) and testosterone (T) co-treatment stimulates both the hypothalmo–pituitary–gonadal (HPG) and hypothalmo–pituitary–interrenal axes, the reproductive and osmoregulatory responses of pre-adult pink salmon Oncorhynchus gorbuscha were compared after GnRH and T administration either alone or in combination. Relative to controls, neither GnRH nor T treatment resulted in significantly greater ovarian or testicular growth, but co-treatment significantly increased ovarian growth after 5 months. Interestingly, the stimulation was undetectable after 3 months. However, once daily photoperiod began shortening after the summer solstice, c. 2 months before the natural spawning date, GnRH+T-treated females were stimulated to produce larger ovaries. Final fish body length and the size of individual eggs did not differ among treatment groups. GnRH+T eggs, however, showed signs of advanced vitellogenesis relative to GnRH-treated and control eggs, whereas T-treated eggs became atretic. Testis size increased significantly from initial values and most males were spermiating, but this growth and development were independent of hormone treatments. Final plasma ion, metabolite and cortisol concentrations did not differ among treatment groups. It is concluded that GnRH+T co-treatment was effective in stimulating female but not male maturation. GnRH and T treatment, however, presumably had little effect on the hypothalmo–pituitary–interrenal axis as observed by ionoregulatory status. [ABSTRACT FROM AUTHOR]

The present study demonstrates that acceleratedphotoperiod advances ovulation in Atlantic salmon, and that exposure to cold water prior to spawning further advances and synchronizes this process while improving egg-survival. High water temperature inhibited both sperm release and ovulation, whereas a GnRHa treatment overrode this temperature effect in most individuals. A decrease in water temperature seemed to accelerate both ovulation and sperm release, and water temperature modulated the plasma 17,20ßP profiles around ovulation and sperm release. The GnRHa treatment markedly increased the volume of strippable milt and the plasma 17,20ßP levels in males. [ABSTRACT FROM AUTHOR]

Compared to the general population, science trainees experience challenges and heightened stressors that often lead to adverse mental health outcomes. With COVID-19, the stressors of social distancing, isolation, truncated lab time, and uncertainty about the future have all likely exacerbated these issues. Now, more than ever, practical and effective interventions are vitally needed to address the core causes of stress among science trainees and increase their resilience. This paper introduces a new resilience program targeted to biomedical trainees and scientists - Becoming a Resilient Scientist Series (BRS), a multi-part workshop complemented by facilitated group discussions all aimed at bolstering resilience, particularly in the context of academic and research environments. To assess the program's efficacy, participants completed resilience measures and related assessments before and after completing the series. The results demonstrate that BRS significantly enhances trainee resilience (primary outcome) and reduces perceived stress, anxiety, and work-related presenteeism, as well as increased adaptability, self-awareness, and self-efficacy (secondary outcomes). Furthermore, program participants reported a high level of satisfaction, a strong willingness to recommend the program to others, and perceived positive changes in their resilience skills. To the best of our knowledge, this is the first resilience program designed explicitly for biomedical trainees and scientists, tailored to their unique professional culture and work environment.

Peripheral feedback of gonadal estrogen to the hypothalamus is critical for reproduction. Bisphenol A (BPA), an environmental pollutant with estrogenic actions, can disrupt this feedback and lead to infertility in both humans and animals. GnRH neurons are essential for reproduction, serving as an important link between brain, pituitary, and gonads. Because GnRH neurons express several receptors that bind estrogen, they are potential targets for endocrine disruptors. However, to date, direct effects of BPA on GnRH neurons have not been shown. This study investigated the effects of BPA on GnRH neuronal activity using an explant model in which large numbers of primary GnRH neurons are maintained and express many of the receptors found in vivo. Because oscillations in intracellular calcium have been shown to correlate with electrical activity in GnRH neurons, calcium imaging was used to assay the effects of BPA. Exposure to 50μM BPA significantly decreased GnRH calcium activity. Blockage of γ-aminobutyric acid ergic and glutamatergic input did not abrogate the inhibitory BPA effect, suggesting direct regulation of GnRH neurons by BPA. In addition to estrogen receptor-β, single-cell RT-PCR analysis confirmed that GnRH neurons express G protein-coupled receptor 30 (G protein-coupled estrogen receptor 1) and estrogen-related receptor-γ, all potential targets for BPA. Perturbation studies of the signaling pathway revealed that the BPA-mediated inhibition of GnRH neuronal activity occurred independent of estrogen receptors, GPER, or estrogen-related receptor-γ, via a noncanonical pathway. These results provide the first evidence of a direct effect of BPA on GnRH neurons.

Metabolic dysfunctions are often linked to reproductive abnormalities. Adiponectin (ADP), a peripheral hormone secreted by white adipose tissue, is important in energy homeostasis and appetite regulation. GnRH neurons are integral components of the reproductive axis, controlling synthesis, and release of gonadotropins. This report examined whether ADP can directly act on GnRH neurons. Double-label immunofluorescence on brain sections from adult female revealed that a subpopulation of GnRH neurons express ADP receptor (AdipoR)2. GnRH/AdipoR2+ cells were distributed throughout the forebrain. To determine the influence of ADP on GnRH neuronal activity and the signal transduction pathway of AdipoR2, GnRH neurons maintained in explants were assayed using whole-cell patch clamping and calcium imaging. This mouse model system circumvents the dispersed distribution of GnRH neurons within the forebrain, making analysis of large numbers of GnRH cells possible. Single-cell PCR analysis and immunocytochemistry confirmed the presence of AdipoR2 in GnRH neurons in explants. Functional analysis revealed 20% of the total GnRH population responded to ADP, exhibiting hyperpolarization or decreased calcium oscillations. Perturbation studies revealed that ADP activates AMP kinase via the protein kinase Cζ/liver kinase B1 pathway. The modulation of GnRH neuronal activity by ADP demonstrated in this report directly links energy balance to neurons controlling reproduction.

Primary cultures obtained from embryonic nasal placodes can maintain olfactory neurons, olfactory ensheathing cells, and large numbers of gonadotropin releasing hormone-1 (GnRH) neurons. Depending on the age of the starting material, one can examine cell interactions important for placode formation or neuronal migration and axonal outgrowth. When generated at E11.5 in mouse, neuronal migration and axon outgrowth away from the main tissue mass occurs. This area of the explant, the periphery, is only a few cells thick. This characteristic offers the opportunity to image single cells and axons and allows pharmacological and molecular manipulations as well as physiological recordings to be performed. Here, we describe a system for culturing nasal explants used in our laboratory. This model system provides a method for obtaining physiological cellular responses with post hoc immunohistochemistry, or gene expression studies, on cells arising from the nasal placode., (© 2012 by John Wiley & Sons, Inc.)

Oscillations in intracellular calcium levels have been described in GnRH-1 neurons in both prenatal and adult cells. However, differences have been reported in the mechanisms underlying these [Ca(2+)](i) oscillations, dependent on the model used. The goal of this study was to address whether these changes depend on the maturation status of GnRH-1 neurons by assaying prenatal GnRH-1 cells maintained in explants, at two different developmental stages. This report documents an increase in the frequency of [Ca(2+)](i) oscillations between 1 and 3 wk of in vitro maturation. During the early stage, [Ca(2+)](i) oscillations are blocked by tetrodotoxin and are mainly triggered by excitatory neurotransmitters, gamma-aminobutyric acid (GABA), and glutamate. In contrast, in the later stage, some cells exhibit residual tetrodotoxin-insensitive [Ca(2+)](i) oscillations, which are sustained by action potential-independent GABA and glutamate release. The strength of these two excitatory inputs remained relatively constant during the maturation process, and the increase in frequency of [Ca(2+)](i) oscillations observed at the later stage is due to a novel excitatory input carried by cholecystokinin. Together, these data indicate developmentally regulated release and interactions of neurotransmitters (known regulators of GnRH-1 cells in adults) and point to extrinsic factors regulating GnRH-1 cellular physiology.

Neuropeptide Y (NPY), a member of the pancreatic polypeptide family, is an orexigenic hormone. GnRH-1 neurons express NPY receptors. This suggests a direct link between metabolic function and reproduction. However, the effect of NPY on GnRH-1 cells has been variable, dependent on metabolic and reproductive status of the animal. This study circumvents these issues by examining the role of NPY on GnRH-1 neuronal activity in an explant model that is based on the extra-central nervous system origin of GnRH-1 neurons. These prenatal GnRH-1 neurons express many receptors found in GnRH-1 neurons in the brain and use similar transduction pathways. In addition, these GnRH-1 cells exhibit spontaneous and ligand-induced oscillations in intracellular calcium as well as pulsatile calcium-controlled GnRH-1 release. Single-cell PCR determined that prenatal GnRH-1 neurons express the G protein-coupled Y1 receptor (Y1R). To address the influence of NPY on GnRH-1 neuronal activity, calcium imaging was used to monitor individual and population dynamics. NPY treatment, mimicked with Y1R agonist, significantly decreased the number of calcium peaks per minute in GnRH-1 neurons and was prevented by a Y1R antagonist. Pertussis toxin blocked the effect of NPY on GnRH-1 neuronal activity, indicating the coupling of Y1R to inhibitory G protein. The NPY-induced inhibition was independent of the adenylate cyclase pathway but mediated by the activation of G protein-coupled inwardly rectifying potassium channels. These results indicate that at an early developmental stage, GnRH-1 neuronal activity can be directly inhibited by NPY via its Y1R.

Atlantic salmon (Salmo salar L.) females (2 SW), maturing for the first time, were reared under one of three temperature regimes (high: 14.3 +/- 0.5 degrees C; natural: 10.6 +/- 1.0 degrees C; and cold: 6.9 +/- 1.0 degrees C) in combination with one of two experimental treatments; an injection of GnRH analogue (GnRHa) contained in biodegradable microspheres, or a sham injection (microspheres only). The six experimental groups were then reared under simulated natural photoperiod for 4 weeks. Blood samples were drawn for analysis of plasma steroid levels and the fish were inspected for ovulation weekly. Batches of stripped eggs were incubated in triplicate incubators in raceways until the eyed stage. Treatment with GnRHa resulted in a substantial advancement and synchronization of ovulation at all temperatures, while exposure to cold water also appeared to advance ovulation slightly. While 75% (warm and cold) to 90% (natural) of GnRHa fish ovulated during the 4-week trial, only 30% of sham-treated females exposed to cold water, and none of the sham-treated fish held at higher temperatures, ovulated during this period. Survival rates of embryos to the eyed-stage were significantly higher for broodstock exposed to cold water. Plasma levels of testosterone (T), 17beta-oestradiol (E2), and 17alpha,20beta-dihydroxy-4-pregnen-3-one (17,20betaP) were all significantly affected by treatment with GnRHa and, to a lesser extent, temperature. The efficiency of GnRHa in counteracting the negative effects of high temperature on ovulation and the associated changes in circulating sex steroids suggest that temperature inhibition operates at least in part at the brain or pituitary.

The zebrafish has proven to be a model system with unparalleled utility in vertebrate genetic and developmental studies. Substantially less attention has been paid to the potential role that zebrafish can play in answering important questions of vertebrate reproductive endocrinology. As an initial step towards exploiting the advantages that the zebrafish model offers, we have characterized their gonadotropin-releasing hormone (GnRH) system at the molecular level. GnRHs comprise a family of highly conserved decapeptide neurohormones widely recognized to orchestrate the hormonal control of reproduction in all vertebrates. We have isolated the gene and cDNA encoding chicken GnRH-II (cGnRH-II) from zebrafish, as well as several kilobases of upstream promoter sequence for this gene. As the gene encoding salmon GnRH (sGnRH) has been previously isolated (Torgersen et al, 2002), this is the second GnRH gene isolated from zebrafish to date. We have localized expression of these two genes in the brains of reproductively mature zebrafish using in situ hybridization. sGnRH is localized to the olfactory bulb-terminal nerve region (OB-TN), the ventral telencephalon-preoptic area (VT-POA) and, as we report here for the first time in any teleost species, the hindbrain. cGnRH-II is expressed exclusively in the midbrain, as has been found in all other jawed vertebrate species examined. Finally, the levels of both GnRH peptides in pituitaries of reproductively mature zebrafish were quantified using specific ELISAs. sGnRH pituitary peptide levels were shown to be 3- to 4-fold higher than cGnRH-II pituitary peptide. The cumulative results of these experiments allow us to conclude that zebrafish express just two forms of GnRH in a site-specific manner within the brain, and that sGnRH is the hypophysiotropic GnRH form. This work lays the foundation for further research into the control of reproduction in zebrafish, such as the functional significance of multiple GnRHs in vertebrates, and the molecular mechanisms controlling tissue-specific GnRH expression.

Three forms of GnRH, chicken (c) GnRH-II, salmon (s) and seabream (sb) GnRH, were immunologically characterized in the brain and pituitary of turbot by ELISA. cGnRH-II and sGnRH were detected in the brain, while sbGnRH and sGnRH (but not cGnRH-II) were detected in the pituitary. In females, the levels of cGnRH-II in the turbot brain extracts increased from May to July, concomitant with an increase in oocyte diameter. In the pituitary, sbGnRH was found to be the dominant form, with levels 100-600-fold those of sGnRH. Both sGnRH and sbGnRH in the pituitary showed variation during the spawning season; sbGnRH increased from May to July and correlated with the increase in oocyte diameter, while sGnRH decreased. The overall patterns were the same for male turbot, although levels were generally lower. These findings suggest that sbGnRH could be controlling reproduction in the turbot. However, the seasonal variation in sGnRH indicates a potential physiological role in turbot reproduction. This study gives the first immunological indications that sbGnRH is present in the pituitary of a pleuronectiform fish, and will provide the basis for further studies on the endocrine regulation of reproduction in flatfish.