Abstract
The control of ovulation helps guarantee the success of reproduction and as such, contributes to the fitness of a species. In mammals, two types of ovulation are observed: induced and spontaneous ovulation. Recent work on camelids, that are induced ovulators, highlighted the role of a factor present in seminal plasma, beta Nerve Growth Factor (β-NGF), as the factor that triggers ovulation in a GnRH dependent manner. In the present work, we characterized alpaca β-NGF (aβ-NGF) and its 3D structure and compared it with human recombinant β-NGF (hβ-NGF). We showed that the β-NGF enriched fraction of alpaca semen and the human recombinant protein, both stimulated spontaneous electrical activity of primary GnRH neurons derived from mouse embryonic olfactory placodes. This effect was dose-dependent and mediated by p75 receptor signaling. P75 receptors were found expressed in vitro by olfactory ensheathing cells (OEC) in close association with GnRH neurons and in vivo by tanycytes in close vicinity to GnRH fibers in adult mouse. Altogether, these results suggested that β-NGF induced ovulation through an increase in GnRH secretion provoked by a glial dependent P75 mediated mechanism.
Highlights
Two modes of ovulation have been described in mammals: spontaneous ovulation and induced ovulation
Our study showed that recombinant human β-NGF (hβ-NGF) and enriched fraction of alpaca seminal plasma alpaca β-NGF (aβ-NGF) increased gonadotropin releasing hormone (GnRH) neurons spontaneaous electrical activity in a dose-dependant manner
This effect was mediated by the P75 neurotrophin receptor but not by TrkA. p75 receptors were expressed by olfactory ensheathing cells in vitro and by tanycytes of the median eminence in adult mice, at the vicinity of GnRH nerve terminals suggesting a indirect effect on GnRH neurons
Summary
Two modes of ovulation have been described in mammals: spontaneous ovulation and induced ovulation. Spontaneous ovulation occurs in many mammalian species (mouse, rat, bovine, ovine, equine, primates). Induced ovulation has been well studied in c amelids[1] In these species, ovulation occurs after mating in more than 95% of females. OIF activity was conserved in these species since equine and porcine seminal plasma induced ovulation in prepubertal mice[13]. Our study showed that recombinant hβ-NGF and enriched fraction of alpaca seminal plasma aβ-NGF increased GnRH neurons spontaneaous electrical activity in a dose-dependant manner. This effect was mediated by the P75 neurotrophin receptor but not by TrkA. This effect was mediated by the P75 neurotrophin receptor but not by TrkA. p75 receptors were expressed by olfactory ensheathing cells in vitro and by tanycytes of the median eminence in adult mice, at the vicinity of GnRH nerve terminals suggesting a indirect effect on GnRH neurons
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