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Friday, February 14, 2003

Why Don't You Come Up and See My Pheromenes Dear

On this special day devoted to lovers everywhere more scientific info unveiling some of loves chemical mysteries. Among other things I learnt today is the fact that mice are active largely at night - because the night, of course, belongs to lovers - so their vision is generally a poor way of gathering information. Instead mice use their auxiliary nose -- known as their "vomeronasal organ" -- which consequently plays the crucial role in a mouse's life. The vomeronasal organ is apparently extremely small and highly sensitive: there, I always new small organs had some definite selection advantages.

Howard Hughes Medical Institute researchers are beginning to unravel how a mysterious sixth sense guides animal attraction. The scientists have made the first-ever recordings of patterns of brain activity in a mouse as it explores the sex and identity of a newly encountered animal.The research team, led by Lawrence C. Katz, a Howard Hughes Medical Institute investigator at Duke University Medical Center, recorded the firing of neurons in the accessory olfactory bulb, part of a poorly understood sensory pathway that is thought to be important in sex discrimination and social behavior in most mammals. The results, to be published in a forthcoming issue of the journal Science, show that chemical signals called pheromones trigger highly specific patterns of neural excitation in the brain. These “pheromone images” provide vital information about the sexual receptiveness of females and the dominance hierarchy in males, among other things, said Katz. “Mice, which live in the darkness in the wild, can readily identify each other on the basis of a pheromonal image rather than a visual image,” said Katz.

Both wild and domestic animals, such as dogs and cats, collect pheromone signals through the “flehmen” response, in which the upper lip curls back during exploration of the oral and anogenital areas of other animals during social encounters. These pheromone signals are collected by the vomeronasal organ (VNO), a hollow tube in the nasal cavity. Sensory neurons lining the VNO, in turn, stimulate neurons in the accessory olfactory bulb, a part of the central nervous system. Finally, signals are sent to the amygdala, a part of the brain responsible for basic drives, such as fear, aggression, mating behavior and maternal instincts. The information contained in pheromone signals is key to survival and reproduction, said Katz. Male mice establish dominance hierarchies, so they need to know if another male is dominant or non-dominant. In addition, males respond to females who are in estrus because they smell differently. “In essence,” said Katz, “these pheromonal cues help mice decide ‘should I mate or fight.’” Important clues to the VNO’s importance in sex recognition have emerged from genetic studies. For example, HHMI investigator Catherine Dulac and her colleagues at Harvard University reported in January 2002 that mice lacking a key molecule in the pheromone-signaling pathway were unable to distinguish males from females and behaved as if all mice were female.
Source: Science Daily

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