Men and women might appear to come from different planets, but in reality, male and female brains are largely similar. So similar, in fact, that at the flip of a single genetic switch, calm, nurturing female mice can be turned into aggressive, rump-sniffing Casanovas – according to a study conducted by Dr. Tali Kimchi, who recently joined the Weizmann Institute's Neurobiology Department.
While carrying out postdoctoral research at Harvard University in the laboratory of Prof. Catherine Dulac, Kimchi found that the behavior of female mice crucially depended on pheromones, the subtle scents that animals secrete to communicate with one another and attract the opposite sex. When Kimchi deprived these mice of just one gene – one responsible for picking up the pheromone signal – the mouse moms started neglecting their pups and failed to protect them. At the same time, they began to display typical male sexual behaviors: They sniffed and chased potential mates, tried to mount them with pelvis-thrusting movements and even emitted high-pitched courtship whistles, of which females were previously thought incapable.
This macho display by the female mice suggests that their brains are wired for both female and male behaviors, and that pheromones probably suppress the male-typical behaviors and turn on the female-typical behaviors. These findings were reported in Nature, which ran a News and Views commentary entitled "Females Can Also Be from Mars."
At the Weizmann Institute, Kimchi will continue to explore the role of pheromones in masculine and feminine behaviors. She will investigate the hormonal, genetic and neurochemical basis of pheromone activity while putting emphasis on both social and reproductive behaviors.
In her new lab, genetically modified mice will be housed in large, enriched enclosures and be monitored by several different types of surveillance equipment, including infrared cameras to closely observe the social interactions of the mice night and day, and microphones to eavesdrop on their "conversations." In contrast to reality TV shows, which usually block out intimate moments, this "Big Brother" setup will pay special attention to the sexual and reproductive activity of the mice. The scientists will strive to reveal the factors controlling such behaviors as making the distinction between males and females, fighting over desirable mates and taking care of pups.
Kimchi works with dark-furred mice bred from animals caught in the wild. These are in many ways closer to nature than their laboratory-bred counterparts, even though they are much smaller, quicker and more difficult to study. She focuses on female mice, which pose a particular challenge as their behavior is less predictable than that of the males. For example, a male mouse can almost always be counted upon to attack a rival male or try to mount a female in heat, whereas it's hard to predict how a female mouse will act in many situations.
Kimchi's research aims at casting new light on the biological roots of behaviors typically viewed as masculine or feminine. For more than half a century, scientists have believed that males and females were set apart mainly by sex hormones that controlled hard-wired brain circuits. Recent studies by Kimchi and others, however, suggest a different view: Gender-specific behaviors stem from small subsets of neurons "switched" on or off by pheromones and other sensory signals. Interestingly, the macho females in Kimchi's studies had normal female hormones and estrous cycles.
A long-term goal of this project is to discover new genes and neuronal circuitry that govern the physiology and reproductive behavior of mammals. Kimchi's findings might, for example, improve our understanding of mental disorders believed to be related to a person's gender, such as autism, sexual dysfunction, and mood and anxiety-related disorders.
A Head Start in Science
When Dr. Tali Kimchi went for walks with her parents at the age of four, she would occasionally stop them so that she could observe rows of ants crossing the road. For as long as she can remember, she always wanted to study animal behavior and other natural phenomena.
During her Ph.D. studies in Tel Aviv University's Department of Zoology under the guidance of Prof. Joseph Terkel, she provided fascinating insights into the navigational behavior of the blind mole rat, a 25-cm-long rodent that lives underground, has no eyes and looks like a furry sausage with sharp front teeth. Kimchi found that in digging its tunnels in search of food and mates,the mole rat chooses its course by using the Earth's magnetic field like a compass. When this blind rodent encounters an obstacle, it always burrows its tunnel along the shortest possible detour. In doing so, Kimchi discovered, the mole rat relies on a peculiar natural "radar": It bangs its head against the tunnel wall to create vibrations, detects the reverberations with its feet and processes these signals to identify the optimal route for digging.
Dr. Tali Kimchi's research is supported by the Carl and Micaela Einhorn-Dominic Brain Research Institute; Rina Mayer, Israel; and Esther Smidof, Switzerland.