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First published online October 18, 2006
Journal of Experimental Biology 209, vi (2006)
Copyright © 2006 The Company of Biologists Limited
doi: 10.1242/jeb.02549
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Outside JEB |
MALE NEURONS RESPOND TO FEMALE PHEROMONE
Veterinary University Vienna
Teresa.Valencak{at}vu-wien.ac.at
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Instead of sending a Valentines card on February 14th, female snakes produce a pheromone when meeting a handsome partner. Once vapourised, the snake love potion is detected by the recipient's vomeronasal organ, the vertebrate's most important chemoreceptive organ. While behavioural studies have already shown that this organ is involved in pheromone perception (males lacking the organ cannot respond to pheromones), the physiological basis of the vomeronasal organ's response remained unclear. To address this issue, Guang-Zhe Huang, from the Downstate Medical Center in New York, and his colleagues, tested the effects of the female pheromone on male vomeronasal neurons. They isolated vomeronasal organs from male red-sided garter snakes, exposed them to pheromones isolated from females of the same species and measured the electrophysiological response of the neurons.
Unfortunately, the pheromone is insoluble in water so Huang and colleagues tried solubilising the pheromone in a homogenate of the Harderian gland, a large reptilian gland whose secretions directly pass into the vomeronasal organ. Amazingly, this inspired step worked, allowing the team to test the vomeronasal organ's receptor cell responses.
Initially, Huang and colleagues measured vomeronasal organ levels of the cell secondary messenger, IP3, in response to the pheromone and found that it increased by more than 200%, demonstrating that the pheromone activates neurons in the vomeronasal sensory epithelium. They also found that the pheromone induced measurable inward currents in male vomeronasal organ neurons, which increased as they raised the pheromone dose. Even more interestingly, the team found that the amplitude of the pheromone-induced current was dose dependent, so they concluded that there are multiple pheromone receptors on male garter snake vomeronasal neurons and that pheromone binding to neurones facilitates further binding cooperatively. Stimulation with female pheromone also increased the neurone's membrane conductance, indicating that ion channels open in response to the pheromone, membranes depolarise and action potentials are initiated.
Finally, Huang and his colleagues examined whether the female's pheromone also affected female vomeronasal organ neurons, and found that female snake vomeronasal neurons did not respond at all to the pheromone. The researchers concluded, that the pheromone response originates at the vomeronasal organ and not in the central nervous system. Interestingly, behavioural observations underline this finding, as female snakes have never been observed to follow trails left by other females or respond to the female perfume.
Huang's study provides the first evidence of an electrophysiological response to a purified pheromone in a reptile and demonstrates that the response is sexually dimorphic, a finding which corresponds to behavioural observations in snakes. So, it seems that mate choice is a matter of smell rather than taste from the male red-garter snake's perspective.
References
Huang, G. Z., Zhang, J. J., Wang, D., Mason, R. T. and Halpern
M. (2006). Female snake sex pheromone induces membrane
responses in vomeronasal sensory neurons of male snakes. Chem.
Senses 31,521
-529.
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