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Today, The Visible Embryo is linked to over 600 educational institutions and is viewed by more than 1 million visitors each month. The field of early embryology has grown to include the identification of the stem cell as not only critical to organogenesis in the embryo, but equally critical to organ function and repair in the adult human. The identification and understanding of genetic malfunction, inflammatory responses, and the progression in chronic disease, begins with a grounding in primary cellular and systemic functions manifested in the study of the early embryo.

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Pregnancy Timeline by SemestersFetal liver is producing blood cellsHead may position into pelvisBrain convolutions beginFull TermWhite fat begins to be madeWhite fat begins to be madeHead may position into pelvisImmune system beginningImmune system beginningPeriod of rapid brain growthBrain convolutions beginLungs begin to produce surfactantSensory brain waves begin to activateSensory brain waves begin to activateInner Ear Bones HardenBone marrow starts making blood cellsBone marrow starts making blood cellsBrown fat surrounds lymphatic systemFetal sexual organs visibleFinger and toe prints appearFinger and toe prints appearHeartbeat can be detectedHeartbeat can be detectedBasic Brain Structure in PlaceThe Appearance of SomitesFirst Detectable Brain WavesA Four Chambered HeartBeginning Cerebral HemispheresFemale Reproductive SystemEnd of Embryonic PeriodEnd of Embryonic PeriodFirst Thin Layer of Skin AppearsThird TrimesterSecond TrimesterFirst TrimesterFertilizationDevelopmental Timeline
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Home | Pregnancy Timeline | News Alerts |News Archive Nov 18, 2014

Kisspeptin is a small protein that stimulates GnRH neurons. Male mice lacking kisspeptin receptors
on their GnRH neurons do not experience the usual testosterone surge at birth.
As a result, adult males have female-like brain characteristics.
Image credit: The Global Library of Women's Medicine

 







 

 

How the male brain is molded

Researchers have discovered that neural circuitry previously identified as vital for triggering ovulation and maintaining fertility also is key to moulding the male brain.

In new research appearing in the Journal of Neuroscience, a team led by Professor Allan Herbison found that male-specific signals generated by Gonadotropin-releasing hormone (GnRH) neurons of new-born mice are crucial in generating a testosterone surge up to five hours after birth - but only in males. This brief and powerful increase in testosterone is shown to cause the male brain to develop differently than a female's.

Professor Herbison adds that sex differences in brain function are established during the later stages of fetal development as well as around birth, but the actual cellular mechanisms underlying these important changes remained unknown.


Through a series of investigations in mice, Dr. Herbison and colleagues found that a small group of GnRH neurons in the brain's hypothalamus become active only in new-born males, and not females. Also, they found that a small population of kisspeptin neurons only appear at birth, but just in males.


Kisspeptin is a small protein that stimulates GnRH neurons. Last year Professor Herbison and colleagues published a landmark study detailing how it acts as a master controller in reproduction.

In their latest investigations, the researchers show that male mice lacking kisspeptin receptors on their GnRH neurons do not experience the usual testosterone surge at birth. And they determined that, even as adult males, these mice had female-like brain characteristics.

According to Professor Herbison, the team's latest findings reveal that kisspeptin, only identified as playing a role in fertility in the past decade, is a much more remarkable molecule than previously thought.*


"Not only does the kisspeptin signal act as a master switch for puberty and ovulation, we show how in the first hours of drawing breath it also triggers our brains to develop differently according to our sex."

Allan Herbison PhD,  Department of Physiology, Otago School of Medical Sciences, Dunedin, New Zealand


Abstract
Acquisition of a mature pattern of gonadotropin-releasing hormone (GnRH) secretion from the CNS is a hallmark of the pubertal process. Little is known about GnRH release during sexual maturation, but it is assumed to be minimal before later stages of puberty. We studied spontaneous GnRH secretion in brain slices from male mice during perinatal and postnatal development using fast-scan cyclic voltammetry (FSCV) to detect directly the oxidation of secreted GnRH. There was good correspondence between the frequency of GnRH release detected by FSCV in the median eminence of slices from adults with previous reports of in vivo luteinizing hormone (LH) pulse frequency. The frequency of GnRH release in the late embryonic stage was surprisingly high, reaching a maximum in newborns and remaining elevated in 1-week-old animals despite low LH levels. Early high-frequency GnRH release was similar in wild-type and kisspeptin knock-out mice indicating that this release is independent of kisspeptin-mediated excitation. In vivo treatment with testosterone or in vitro treatment with gonadotropin-inhibitory hormone (GnIH) reduced GnRH release frequency in slices from 1-week-old mice. RF9, a putative GnIH antagonist, restored GnRH release in slices from testosterone-treated mice, suggesting that testosterone inhibition may be GnIH-dependent. At 2–3 weeks, GnRH release is suppressed before attaining adult patterns. Reduction in early life spontaneous GnRH release frequency coincides with the onset of the ability of exogenous GnRH to induce pituitary LH secretion. These findings suggest that lack of pituitary secretory response, not lack of GnRH release, initially blocks downstream activation of the reproductive system.

The study was undertaken by Professor Allan Herbison and Dr Jenny Clarkson of the Centre for Neuroendocrinology and Department of Physiology in collaboration with researchers in Canada and Germany. The work was supported by the Health Research Council of New Zealand and the former Ministry of Science and Innovation.

*Kisspeptin was originally named after the Hershey Kiss chocolate by US cancer researchers based in Hershey, Pennsylvania. At the time they had no idea that it had a role in fertility.


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