The GnRH System of Seasonal Breeders: Anatomy and Plasticity

Lehman, Michael N.; Goodman, Robert L.; Karsch, Fred J.; Jackson, Gary L.; Berriman, Sandra; Jansen, Heiko T.

doi:10.1016/s0361-9230(97)00225-6

Cited by 72 publications

(46 citation statements)

References 84 publications

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“…In times of reduced energy availability, reproduction is inhibited (Bartness, 1996;Schneider et al, 2000). In addition to mediating the reproductive axis through energetic signaling, estrogen-receptor-positive Arc projections also act on GnRH terminals in the median eminence to modulate their output (Lehman, 1997). Whether kisspeptin neurons specifically mediate these Arc effects on the reproductive axis represent an interesting topic for further inquiry.…”

Section: Discussionmentioning

confidence: 99%

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

Mason

Greives

Scotti

et al. 2007

Hormones and Behavior

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To avoid breeding during unsuitable environmental or physiological circumstances, the reproductive axis adjusts its output in response to fluctuating internal and external conditions. The ability of the reproductive system to alter its activity appropriately in response to these cues has been well established. However, the means by which reproductively relevant cues are interpreted, integrated, and relayed to the reproductive axis remain less well specified. The neuropeptide kisspeptin has been shown to be a potent positive stimulator of the hypothalamo-pituitary-gonadal (HPG) axis, suggesting a possible neural locus for the interpretation/integration of these cues. Because a failure to inhibit reproduction during winter would be maladaptive for short-lived female rodents, female Siberian hamsters (Phodopus sungorus) housed in long and short days hamsters were examined. In long, 'summer' photoperiods, kisspeptin is highly expressed in the anteroventral periventricular nucleus (AVPV), with low expression in the arcuate nucleus (Arc). A striking reversal in this pattern is observed in animals held in short, 'winter' photoperiods, with negligible kisspeptin expression in the AVPV and marked staining in the Arc. Although all studies to date suggest that both populations act to stimulate the reproductive axis, these contrasting expression patterns of AVPV and Arc kisspeptin suggest disparate roles for these two cell populations. Additionally, we found that the stimulatory actions of exogenous kisspeptin are blocked by acyline, a gonadotropin-releasing hormone (GnRH) receptor antagonist, suggesting an action of kisspeptin on the GnRH system rather than pituitary gonadotropes. Finally, females held in short day lengths exhibit a reduced response to exogenous kisspeptin treatment relative to long-day animals. Together, these findings indicate a role for kisspeptin in the AVPV and Arc as an upstream integration center for reproductively-relevant stimuli and point to a dual mechanism of reproductive inhibition in which kisspeptin expression is reduced concomitant with reduced sensitivity of the HPG axis to this peptide.

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Section: Discussionmentioning

confidence: 99%

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

Mason

Greives

Scotti

et al. 2007

Hormones and Behavior

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“…GnRH1 neurons are master regulators of pituitary activation, and dopaminergic suppression of their activity will profoundly influence the release of pituitary hormones, and thus reproductive behavior. Dopaminergic inhibition of GnRH is important for long-term suppression of reproduction, as occurs before puberty (Becú-Villalobos and Libertun, 1995;Gerber et al, 1984;Lamberts and Wuttke, 1981;Terasawa and Fernandez, 2001), during seasonal anoestrus (Lehman et al, 1997) and as a function of social influences (Davis and Fernald, 1990;Darney et al, 1992;Greenwood, 2003). We propose that the presence of multiple, conserved dopaminergic control sites along the HPG axis emphasizes a privileged role for dopamine in regulating vertebrate reproductive behaviors.…”

Section: D2r Agonists Directly Inhibit Gnrh1 Neuronsmentioning

confidence: 99%

Dopaminergic inhibition of gonadotropin-releasing hormone neurons in the cichlid fish,Astatotilapia burtoni

Bryant

Greenwood

Juntti

et al. 2016

Journal of Experimental Biology

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Dopamine regulates reproduction in part by modulating neuronal activity within the hypothalamic-pituitary-gonadal (HPG) axis. Previous studies suggested numerous mechanisms by which dopamine exerts inhibitory control over the HPG axis, ultimately changing the levels of sex steroids that regulate reproductive behaviors. However, it is not known whether these mechanisms are conserved across vertebrate species. In particular, it is unknown whether mechanisms underlying dopaminergic control of reproduction are shared between mammals and teleost fish. In mammals, dopamine directly inhibits gonadotropin-releasing hormone (GnRH1) hypothalamic neurons, the gatekeepers for activation of the HPG axis. Here, we demonstrate, for the first time in teleost fish, dopaminergic control of GnRH1 neurons via direct dopamine type-2-like receptor (D2R)-mediated inhibition within the hypothalamus. These results suggest that direct dopaminergic control of GnRH1 neurons via interactions in the hypothalamus is not exclusive to tetrapod reproductive control, but is likely conserved across vertebrate species.

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“…Of relevance, melatonin does not appear to act directly on gonadotropin-releasing hormone-1 (GnRH-1) neurons (Lehman et al, 1997;Malpaux et al, 1998). A major target appears to be the pars tuberalis (PT) based on binding sites present with greatest density in that organ; however, hypothalamic and other sites were also identified (Bittman and Weaver, 1990).…”

Section: Mammalian Neural Pathway Regulating Seasonal Reproduction (1mentioning

confidence: 99%

Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development

Kuenzel¹,

Kang²,

Zhou³

2015

Poultry Science

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A large number of mammalian, avian, and other vertebrate species are photoperiodic and thereby display a defined time of year when their reproductive system is activated due to an ability to sense seasonal changes in photoperiod. Several reviews have addressed photoperiodism in birds including its proposed mechanisms, regulation of key annual cycle events, and relevance to productivity and fitness of avian species Nicholls et al., 1988;Kuenzel, 1993;Foster et al., 1994;Wilson, 1997;Dawson et al., 2001;Sharp, 2005;Ono et al., 2009;Ubuka et al., 2013). The purpose of this paper is to focus on one aspect of the phenomenon, particularly its sensory component. Decades ago it was proposed that vertebrates possess a photo-neuroendocrine system (PNES) composed of 2 components including (1) the photoperiodic axis (receptors and groups of neurons detecting light or changes in photoperiods, and (2) the traditional hypothalamo-pituitary-gonadal (HPG) axis (Scharrer, 1964). Scharrer's first component, the sensory system, will be addressed herein. A neural pathway is required to detect light information from the environment, integrate it and in some manner connect with the classical HPG axis to regulate reproductive function at the appropri- ABSTRACT In the eyes of mammals, specialized photoreceptors called intrinsically photosensitive retinal ganglion cells (ipRGC) have been identified that sense photoperiodic or daylight exposure, providing them over time with seasonal information. Detectors of photoperiods are critical in vertebrates, particularly for timing the onset of reproduction each year. In birds, the eyes do not appear to monitor photoperiodic information; rather, neurons within at least 4 different brain structures have been proposed to function in this capacity. Specialized neurons, called deep brain photoreceptors (DBP), have been found in the septum and 3 hypothalamic areas. Within each of the 4 brain loci, one or more of 3 unique photopigments, including melanopsin, neuropsin, and vertebrate ancient opsin, have been identified. An experiment was designed to characterize electrophysiological responses of neurons proposed to be avian DBP following light stimulation. A second study used immature chicks raised under shortday photoperiods and transferred to long day lengths. Gene expression of photopigments was then determined in 3 septal-hypothalamic regions. Preliminary electrophysiological data obtained from patch-clamping neurons in brain slices have shown that bipolar neurons in the lateral septal organ responded to photostimulation comparable with mammalian ipRGC, particularly by showing depolarization and a delayed, slow response to directed light stimulation. Utilizing real-time reversetranscription PCR, it was found that all 3 photopigments showed significantly increased gene expression in the septal-hypothalamic regions in chicks on the third day after being transferred to long-day photoperiods. Each dissected region contained structures previously proposed to have DBP. The highly significant increased ge...

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The GnRH System of Seasonal Breeders: Anatomy and Plasticity

Cited by 72 publications

References 84 publications

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

Suppression of kisspeptin expression and gonadotropic axis sensitivity following exposure to inhibitory day lengths in female Siberian hamsters

Dopaminergic inhibition of gonadotropin-releasing hormone neurons in the cichlid fish,Astatotilapia burtoni

Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development

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