Abstract
Fertility relies on the proper functioning of the hypothalamic–pituitary–gonadal axis. The hormonal cascade begins with hypothalamic neurons secreting gonadotropin-releasing hormone (GnRH) into the hypophyseal portal system. In turn, the GnRH-activated gonadotrophs in the anterior pituitary release gonadotropins, which then act on the gonads to regulate gametogenesis and sex steroidogenesis. Finally, sex steroids close this axis by feeding back to the hypothalamus. Despite this seeming straightforwardness, the axis is orchestrated by a complex neuronal network in the central nervous system. For reproductive success, GnRH neurons, the final output of this network, must integrate and translate a wide range of cues, both environmental and physiological, to the gonadotrophs via pulsatile GnRH secretion. This secretory profile is critical for gonadotropic function, yet the mechanisms underlying these pulses remain unknown. Literature supports both intrinsically and extrinsically driven GnRH neuronal activity. However, the caveat of the techniques supporting either one of the two hypotheses is the gap between events recorded at a single-cell level and GnRH secretion measured at the population level. This review aims to compile data about GnRH neuronal activity focusing on the physiological output, GnRH secretion.
Highlights
Fertility and its onset, puberty, are integrated phenomena
The hypothesis of an intrinsic pulse generator comes from in vitro models for gonadotropin-releasing hormone (GnRH) neurons: [1] mouse cell lines obtained by immortalization, GT1 [60], and [2] primary GnRH cells maintained in organotypic cultures of olfactory placodes, i.e., nasal explants [61,62,63,64]
As in many other fields, the knowledge is limited by techniques and none of the “classical” tools available in neuroscience are readily usable for GnRH neurons
Summary
Specialty section: This article was submitted to Neuroendocrine Science, a section of the journal
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