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.
Source:University of California - Berkeley