The direct response of the gonads to cues of stress in a temperate songbird species is season-dependent

The gonadotropin releasing hormone (GnRH) system in the hypothalamus is often considered the final point in integration of environmental cues as they pertain to the reproductive axis. However, cues such as stress and food availability are detectable in the plasma (as glucocorticoid and metabolic fuel fluctuations). Vertebrate gonads express glucocorticoid receptor, therefore we hypothesized that the gonads can detect and respond directly to cues of stress. We provide evidence here that, in addition to regulation by the brain, the gonads of European starlings (Sturnus vulgaris) respond directly to fluctuations in corticosterone and metabolic fuels by modulating sex steroid secretion. Using a 4-h gonad culture, we show that physiologically-relevant concentrations of corticosterone and metabolic stress (via use of the glucose utilization inhibitor 2-deoxy-D-glucose and the fatty acid oxidation inhibitor ethyl 2-mercaptoacetate (2DG/MA)) can directly decrease testosterone and estradiol secretion from luteinizing hormone and follicle-stimulating hormone (LH/FSH)-stimulated testes and ovaries. This effect is regulated seasonally. Prior to the breeding season, testes and ovaries respond to corticosterone and 2DG/MA by significantly decreasing gonadal steroid release. Within the breeding season, the testes do not respond to these cues of stress, while the ovaries respond only to corticosterone. This seasonal difference in response may be due in part to the influence of these cues of stress on gonadal neuropeptide expression: corticosterone upregulates GnIH expression in the testes while metabolic stress upregulates GnIH in the ovaries. Thus the gonads can directly respond to fluctuations in corticosterone and metabolic fuels during a time of critical importance to the onset of breeding.

Effects of peripubertal gonadotropin-releasing hormone agonist on brain development in sheep--a magnetic resonance imaging study

In many species sexual dimorphisms in brain structures and functions have been documented. In ovine model, we have previously demonstrated that peri-pubertal pharmacological blockade of gonadotropin releasing hormone (GnRH) action increased sex-differences of executive emotional behavior. The structural substrate of this behavioral alteration however is unknown. In this magnetic resonance image (MRI) study on the same animals, we investigated the effects of GnRH agonist (GnRHa) treatment on the volume of total brain, hippocampus and amygdala. In total 41 brains (17 treated; 10 females and 7 males, and 24 controls; 11 females and 13 males) were included in the MRI study. Image acquisition was performed with 3-T MRI scanner. Segmentation of the amygdala and the hippocampus was done by manual tracing and total gray and white matter volumes were estimated by means of automated brain volume segmentation of the individual T2-weighted MRI volumes. Statistical comparisons were performed with general linear models. Highly significant GnRHa treatment effects were found on the volume of left and right amygdala, indicating larger amygdalae in treated animals. Significant sex differences were found for total gray matter and right amygdala, indicating larger volumes in male compared to female animals. Additionally, we observed a significant interaction between sex and treatment on left amygdala volume, indicating stronger effects of treatment in female compared to male animals. The effects of GnRHa treatment on amygdala volumes indicate that increasing GnRH concentration during puberty may have an important impact on normal brain development in mammals. These novel findings substantiate the need for further studies investigating potential neurobiological side effects of GnRHa treatment on the brains of young animals and humans.

Individual variation in testosterone and parental care in a female songbird; the dark-eyed junco (Junco hyemalis)

When competition for sex-specific resources overlaps in time with offspring production and care, trade-offs can occur. Steroid hormones, particularly testosterone (T), play a crucial role in mediating such trade-offs in males, often increasing competitive behaviors while decreasing paternal behavior. Recent research has shown that females also face such trade-offs; however, we know little about the role of T in mediating female phenotypes in general, and the role of T in mediating trade-offs in females in particular. Here we examine the relationship between individual variation in maternal effort and endogenous T in the dark-eyed junco, a common songbird. Specifically, we measure circulating T before and after a physiological challenge (injection of gonadotropin releasing hormone, GnRH), and determine whether either measure is related to provisioning, brooding, or the amount of T sequestered in egg yolk. We found that females producing more T in response to a challenge spent less time brooding nestlings, but provisioned nestlings more frequently, and deposited more T in their eggs. These findings suggest that, while T is likely important in mediating maternal phenotypes and female life history tradeoffs, the direction of the relationships between T and phenotype may differ from what is generally observed in males, and that high levels of endogenous T are not necessarily as costly as previous work might suggest.

Peri-pubertal gonadotropin-releasing hormone agonist treatment affects sex biased gene expression of amygdala in sheep

The nature of hormonal involvement in pubertal brain development has attracted wide interest. Structural changes within the brain that occur during pubertal development appear mainly in regions closely linked with emotion, motivation and cognitive functions. Using a sheep model, we have previously shown that peri-pubertal pharmacological blockade of gonadotropin releasing hormone (GnRH) receptors, results in exaggerated sex-differences in cognitive executive function and emotional control, as well as sex and hemisphere specific patterns of expression of hippocampal genes associated with synaptic plasticity and endocrine signaling. In this study, we explored effects of this treatment regime on the gene expression profile of the ovine amygdala. The study was conducted with 30 same-sex twin lambs (14 female and 16 male), half of which were treated with the GnRH agonist (GnRHa) goserelin acetate every 4th week, beginning before puberty, until approximately 50 weeks of age. Gene expression profiles of the left and right amygdala were measured using 8×15 K Agilent ovine microarrays. Differential expression of selected genes was confirmed by qRT-PCR (Quantitative real time PCR). Networking analyses and Gene Ontology (GO) Term analyses were performed with Ingenuity Pathway Analysis (IPA), version 7.5 and DAVID (Database for Annotation, Visualization and integrated Discovery) version 6.7 software packages, respectively. GnRHa treatment was associated with significant sex- and hemisphere-specific differential patterns of gene expression. GnRHa treatment was associated with differential expression of 432 (|logFC|>0.3, adj. p value <0.05) and 46 (p value <0.0.5) genes in the left and right amygdala, respectively, of female animals, relative to the reference sample which consisted of all a pooled sample from control and treated animals of both sexes. No genes were found to be differentially expressed as a result of GnRHa treatment in the male animals. The results indicated that GnRH may, directly and/or indirectly, be involved in the regulation of sex- and hemisphere-specific differential expression of genes in the amygdala. This finding should be considered when long-term peri-pubertal GnRHa treatment is used in children.

In utero exposure to DBP stimulates release of GnRH by increasing the secretion of PGE2 in the astrocytes of the hypothalamus in the offspring mice

Di-n-butyl phthalate (DBP), the most commonly used plasticizer and typical endocrine disrupting chemicals (EDCs), has shown its characteristics of causing reproductive and developmental toxicity in males, while the neuroendocrine toxicity induced by DBP exposure in utero and the mechanism beneath still remain unclear. Here, the pregnant mice were treated with corn oil (control) or DBP at three different doses by oral gavage during gestational days (GD) 12.5-21.5. The results showed that in utero exposure to DBP induced a significant increase of gonadotropin releasing hormone (GnRH) content in serum, as well as activation and proliferation of astrocytes in the hypothalamus of offspring male mice on postnatal day (PND) 22. However, in in vitro study, mono-n-butyl phthalate (MBP), the metabolite of DBP, could not increase the release of GnRH after GnRH neurons were exposed to MBP. Further studies identified that MBP-mediated activation and proliferation of astrocytes resulted in increased secretion of prostaglandin E2 (PGE2), which might be responsible for the increased release of GnRH from GnRH neurons. This study highlights the neuroendocrine toxicity of current plasticizer DBP exposure, laying the foundation for identifying potential molecular targets for related diseases.

GnRH protective effects against long-term potentiation impairment induced by AANAT-siRNA

There is an interplay between the gonadotropin-releasing hormone (GnRH) and melatoninergic systems. The key enzyme of melatonin synthesis (arylalkylamine N-acetyltransferase, AANAT), and GnRH receptors are expressed in the hippocampus. While it has been shown that hippocampal AANAT enzyme activity is necessary for proper hippocampal cognitive function, their role in long-term potentiation (LTP) induction is not fully understood. In current study, the impact of GnRH on LTP induction was investigated, while hippocampal melatonin synthesis had been inhibited. The melatonin synthesis was inhibited by AANAT-siRNA administration, and LTP was induced using in vivo field potential electrophysiological recording. Animals were divided into 5 groups: Intact, vehicle, siRNA, GnRH and siRNA+GnRH. All animals, except intact group, experienced the stereotaxic surgery and intra-hippocampal cannulation to receive vehicle agent, AANAT siRNA (0.5 μg/hip), GnRH (1 ng/rat), and AANAT siRNA+GnRH. The recognition memory was assessed by Novel object recognition test. The field potential electrophysiology experiment was conducted by stimulating the Schaffer collateral pathway, and LTP induction was carried out through high-frequency stimulation (HFS). After recording, animals' brain was isolated and quickly frozen for further hippocampal melatonin levels measurement by LC-MS and AANAT mRNA levels by qRT-PCR. GnRH injection in the hippocampus increased local AANAT-mRNA expression and melatonin levels. GnRH-treated animals displayed higher LTP amplitude compared to intact, vehicle and siRNA groups. While the reduction in hippocampal melatonin levels by AANAT-siRNA inhibited LTP and impaired recognition memory, the GnRH prevented these adverse effects. The data suggests that GnRH have protective effects against AANAT-siRNA-induced LTP decline. The protective mechanism at least partially, may be related to the increased expression of local AANAT-mRNA.