Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

New brain hormone puts brakes on reproduction

08.02.2006


Hormone discovered in bird brains also plays major role in mammalian reproductive system



University of California, Berkeley, researchers have discovered a new actor in the mammalian reproductive system, a hormone that fills a role long suspected, but until now undetected.

The hormone, a small protein, or peptide, called gonadotropin-inhibitory hormone (GnIH), puts the brakes on reproduction by directly inhibiting the action of the central hormone of the reproductive system - gonadotropin releasing hormone (GnRH). GnRH stimulates the pituitary gland to activate the reproductive system, whereas GnIH appears to reduce the effects of GnRH stimulation.


Researchers have long sought inhibitors of pituitary gonadotropins, but many had come to believe that such a direct inhibitor was unlikely in the complex cast of hormones and factors in the reproductive system. The inhibiting or braking hormone may complement the "gas pedal" role played by another recently discovered hormone, kisspeptin, that stimulates GnRH.

The discovery in rats, mice and hamsters of this new system for regulating reproduction strongly suggests that the hormone plays a similar role in the reproductive systems of humans and other mammals. The human genome, in fact, contains a gene for GnIH.

If the new finding is mirrored in humans and other mammals, it would offer physicians another means of tweaking the reproductive system to fix problems ranging from infertility to precocious puberty, and also provide animal breeders with a new way to manipulate the productivity of livestock.

The findings by Kriegsfeld and colleagues are reported this week in the online early edition of Proceedings of the National Academy of Sciences.

The human reproductive system is regulated like a thermostat, with a number of hormones and factors produced along the "reproductive axis" acting via feedback loops to keep the body’s hormones within the optimal range for fertility and successful mating. The head of the axis is the brain’s GnRH-producing hypothalamus, which communicates via a blood portal with the anterior pituitary and stimulates production of the hormones gonadotropin, luteinizing hormone and follicle stimulating hormone.

These hormones are dumped into the bloodstream and make their way to the gonads, where in males they stimulate production of testosterone and the maturation of sperm. In females, the hormones stimulate production of estradiol, a sex steroid hormone and the body’s main form of estrogen, and regulate ovulation, the production of fertile eggs.

Estradiol and testosterone, in turn, feed back on the pituitary to shut down production of pituitary hormones, establishing feedback that keeps the body’s sex hormones on an even keel.

Estradiol also works higher in the brain, on the hypothalamus, to ramp down production of GnRH, but how this works has been a relative mystery. The new study provides an answer: Estradiol stimulates cells in the dorsomedial nucleus of the hypothalamus to produce GnIH, which appears to act directly on cells in the hypothalamus to turn off their production of GnRH.

"Here, we have a novel neural pathway mediating the regulatory actions of sex steroids," said Lance Kriegsfeld, UC Berkeley assistant professor of psychology.

"This is an example of the reproductive system being fine tuned," said George Bentley, UC Berkeley assistant professor of integrative biology. "We know a lot about the gross regulation of the reproductive system, but fine tuning hasn’t been well understood at all."

GnIH was discovered five years ago in quail by Japanese researchers led by Kazuyoshi Tsutsui, a professor on the faculty of integrated arts and sciences at Hiroshima University. The discovery supplied one of the last remaining pieces of the bird’s hormone system that controls reproduction. GnIH seemed to be the missing antagonist that switches off pituitary gonadotropins, and work by Tsutsui and Bentley in quail and white-crowned sparrows confirmed its role in turning down production of GnRH and thus switching off the gonads.

While Bentley collaborated with Tsutsui to determine how GnIH works in birds, the two also teamed up with Kriegsfeld to explore the implications in mammals. Kriegsfeld began collaborating with the group as a postdoctoral fellow working with Rae Silver, Kaplan Professor of Natural and Physical Sciences at Barnard College, and professor of psychology at Columbia University, and has continued this research in his own lab as an assistant professor. Using fluorescent antibodies to GnIH, they were able to locate where in the brain the hormone is made: in the nerves of the dorsomedial hypothalamus. The axons of these nerves project to numerous areas of the brain where nerve cells produce GnRH, and staining showed that these axons contacted GnRH-producing cells, suggesting direct effects.

As in birds, GnIH also rapidly inhibits production of luteinizing hormone by the pituitary, they showed. Along with the fact that the cells containing GnIH also have receptors for estrogen-like compounds such as estradiol, the combined evidence suggests that GnIH is a direct inhibitor of GnRH.

Because the brain cells producing and secreting GnIH send their axons into many areas of the brain, GnIH may have other effects on the brain, too.

"Though we don’t know in mammals where the receptors are for GnIH, it looks like the hormone produces multiple effects in the brain," Bentley said. "In birds, the hormone not only affects reproductive hormones, but also sexual behavior in females, such as readiness to copulate."

Interestingly, the neurons producing GnIH are in an area of the brain, the dorsomedial nucleus of the hypothalamus, that coordinates and integrates information from external stimuli, the senses and from motivational and emotional inputs.

"It’s likely serving lots of functions relating to motivated behaviors, such as reproduction or feeding," Kriegsfeld said.

Kriegsfeld and Bentley plan to continue their investigation of the role of GnIH in birds and mammals, with the assistance of postdoctoral fellow Takayoshi Ubuka, formerly of Tsutsui’s laboratory in Japan, and Tsutsui’s Hiroshima University colleagues, Kazuhiko Inoue and Kazuyoshi Ukena. Also coauthors of the PNAS paper were Dan Feng Mei and Rae Silver of the Barnard College and Columbia University Departments of Psychology, and Alex O. Mason of the UC Berkeley Department of Psychology. Kriegsfeld, Bentley and Mason also are members of UC Berkeley’s Helen Wills Neuroscience Institute. Tsutsui and Ukena also are affiliated with the Core Research for Evolutional Science and Technology at Tokyo’s Japan Science and Technology Corporation. Rae Silver is also Professor in the Department of Anatomy and Cell Biology at Columbia University Health Sciences.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Life Sciences:

nachricht How brains surrender to sleep
23.06.2017 | IMP - Forschungsinstitut für Molekulare Pathologie GmbH

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Quantum thermometer or optical refrigerator?

23.06.2017 | Physics and Astronomy

A 100-year-old physics problem has been solved at EPFL

23.06.2017 | Physics and Astronomy

Equipping form with function

23.06.2017 | Information Technology

VideoLinks
B2B-VideoLinks
More VideoLinks >>>