The latest research related to behavioral optogenetics is a study at Yale University that investigates predatory hunting behavior in mice. The paper, published in the January 12 issue of Cell, describes how the researchers isolated the brain circuitry that coordinates hunting. One set of neurons in the amygdala, the brain's center of emotion and motivation, cues the animal to pursue prey. Another set signals the animal to use its jaw and neck muscles to bite and kill.
The researchers used a blue DPSS 473 nm laser to selectively excite the neurons. They observed that when the laser was off, the mice behaved normally. But when the laser was turned on, they pursued and bit anything in their path - even bottle caps and wood sticks.
The animals did not, however, attack other mice in the cage. Hunger also affected predatory behavior. Hungry mice more aggressively pursued prey during light stimulation than mice that were not hungry. "The system is not just generalized aggression. It seems to be related to the animal's interest in obtaining food," says lead investigator Ivan de Araujo, Associate Professor of Psychiatry at the Yale University School of Medicine and an Associate Fellow at the John B. Pierce Laboratory.
De Araujo's interest in more natural behaviors like feeding pointed him to a study that had mapped brain areas associated with hunting and eating. Many areas were listed, but one responded almost exclusively to hunting and not to eating. That region, the central nucleus of the amygdala, also had projections that were linked to areas that control hunting muscles, such as the jaw and neck. "This area was perfectly compatible with an activation system that drives the motor behavior associated with hunting," he says.
During the investigation, they found that one set of neurons controlled pursuit, and another controlled the kill. The researchers also specifically lesioned each type of neuron. They found that, if they lesioned the neurons associated with biting and killing, the animals would pursue the prey but could not kill. The biting force of the jaw was decreased by 50 percent. "They fail to deliver the killing bite," says de Araujo.
The team is now exploring the sensory input into the amygdala to determine what triggers predatory behaviors and investigating how the two modules--one controlling pursuit and the other controlling the kill--are coordinated.
This work was supported by the National Institutes of Health, the National Natural Science Foundation of China, and the Brazilian government. The full paper may be accessed at: Science Direct
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