Bentley's Lab:

IB professor George Bentley looks down at his boots and attempts to explain why they've got a bit of manure on them. "I'm going out to a cow farm to chase starlings this morning," he says. He's wearing his field boots, still covered in evidence of previous visits to the cow farm. Bentley studies how hormones in birds' brains respond to environmental information, and how those hormones influence bird physiology and behavior.

Chasing starlings is nothing new for Bentley, who grew up in the English countryside, where neighboring farmers would ask him to scare the bothersome birds off their property.

Back then, Bentley was no doubt causing those starlings some stress, and today he is still interested in stressed-out starlings--how stress affects birds' hormones, their reproductive physiology, and their behavior. One main focus in his lab right now is the role of a neuropeptide called gonadotropin-inhibitory hormone (GnIH). This hormone acts to inhibit reproduction, and it may explain why birds (and animals) in captivity do not reproduce.

Birds are excellent models for studying the effects of hormones on the brain. They exhibit seasonal breeding: in spring-time, as the day length grows longer, birds undergo a process akin to puberty. At the end of the breeding season, birds go through a kind of reverse puberty. This sensitivity to day length means that scientists can turn birds' reproductive systems on and off, simply by putting the lights on a timer.

Seasonal breeding is thought to be partly an adaptation to flight. When breeding season is over, birds' reproductive organs shrink in size, so the birds don't need to haul around heavy sex organs all year. Breeding is also timed to coincide with abundant food sources, necessary for feeding their growing offspring.

It was in birds that gonadotropin-inhibitory hormone, or GnIH, was first discovered, in 2000. Bentley and his collaborators have shown that this hormone is also present in mammals--sheep, horses, hamsters and monkeys. Recently Takayoshi Ububuka, a postdoc in Bentley's lab, isolated GnIH from human brains.

GnIH acts to inhibit reproduction, through multiple pathways. It binds to neurons that produce another hormone, called gonadotropin-releasing hormone (GnRH). GnRH is necessary for bird gonads to fully mature. Says Bentley, "GnRH is basically the 'on switch' for reproduction."

At first, Bentley and his collaborators thought that GnIH, the inhibitory hormone, might be responsible for shutting down the reproductive system at the end of the breeding system. They thought that perhaps it was only present towards the end of springtime, when it inhibited GnRH, the hormone that activates reproduction. But, they've found that the inhibitory hormone is present year-round in birds. "We think it's more involved in fine-tuning the start of the breeding season," says Bentley.

Rebecca Calisi, one of Bentley's grad students, has some evidence to suggest that instead of pushing reproduction's stop button at the end of the breeding season, GnIH pushes the pause button at the beginning of the season.

That's an important distinction because once the reproductive system is shut down, says Bentley, "it takes a while to get things going again." Pushing pause gives birds the ability to quickly respond to environmental conditions without missing the opportunity to breed that year.

"A lot of birds in northern temperate zones get ready to breed as a result of increasing day length. But you can imagine in the start of spring weather can be very variable… We think that GnIH can play quite a strong role in timing the actual onset of breeding. It can inhibit reproductive behavior or inhibit final maturation of the follicles in times of inclement weather or lack of nest sites or times of stress," says Bentley.

Nicole Perfito, a Visiting Scholar from the Max-Planck Institute for Ornithology, Vogelwarte Radolfzell in Germany, has been working on the role of GnIH in suspending breeding in Australian zebra finches when drought occurs. Along these lines, Nicolette McGuire, another of Bentley's grad students, is working on how GnIH responds to environmental stimuli and acts within the gonads of birds and mammals, to influence steroid release and associated steroid-dependent reproductive behaviors.

The neuropeptide GnIH inhibits the reproductive system. And so does stress. Bentley is collaborating with IB professor Daniela Kaufer, who studies the effects of stress on the brain, to see if stress increases the levels of GnIH. So far, graduate student Liz Kirby has preliminary evidence that animals under stress do indeed have higher levels of GnIH.

Wild birds do not breed well in captivity, perhaps in response to stress. If GnIH is inhibiting reproduction in captivity, then "the ultimate goal down the line," says Bentley, "is to find a way of inhibiting GnIH in endangered wild species. Not only in birds but in mammals as well. That's my pie in the sky idea."

Bentley started working on endocrine research as an undergraduate in biology at the University of Bristol in England. "In our final year we had to do a 20 week research project," he says. But he didn't get his first choice project. Instead, "I ended up working on circadian rhythms in mice," he says. "And I loved it. I thought this is what I want to do. I want to ask questions and find out things for the first time."

He is now giving other undergrads the opportunity to find out things for the first time. His lab currently employs nine undergraduates, as well as the occasional high school student. Undergraduates and high school students can try out new ideas in the lab, says Bentley. "We can troubleshoot a lot of things with the undergrads, whilst teaching them about the pros and cons of research." In fact, the study of stress and GnIH started out as a high school student's project. "We didn't know if that was going to work out. Noel Cruz got some really good preliminary data, and we're following up on that." Cruz entered the lab via the Eastside Project and is now an undergrad at UC Merced. Emanuel Zamora, a NSF REU student from Whittier College, spent the summer of 2008 piloting another study on GnIH and stress.

Bentley gives lectures for the local chapter of the Audubon Society. And he brings specimens from Berkeley's Museum of Vertebrate Zoology to his kids' school, teaching children ages 3-6 about bird form and function. But the highlight is teaching Berkeley undergrads. Says Bentley, "the undergrads here are really fantastic. They just blow me away. I don't think I should be teaching them sometimes, they're so smart."


Bentley teaches Comparative Endocrinology, IB 138, which focuses on the evolution of hormonal systems. He also co-teaches Animal Behavior, IB 144, as well as a Freshman Seminar on birdsong (IB 24).

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