Researchers discover exactly how pheromones enhances sexual behavior in females but make other males aggressive

June 23, 2017  22:45

Scientists know that pheromones - chemicals produced by animals - affect the behavior of others of their species.

But little is known about how the brain actually converts these chemicals into certain behaviors, especially in mammals.

But new research has shown how a male pheromone in mice enhances sexual behaviors in females, and at the same time enhance aggression in males.

A male mouse pheromone called ESP1 has been shown to enhance sexual behaviors in females, but elicit aggressive behaviors in males exposed to the pheromone along with unfamiliar male urine

The team of Japanese researchers based at the University of Tokyo identified specific neural circuits and neurons in mice that generate a particular behavioral response to specific chemical signals.

In most animals, the sense of smells and sensory perception of other chemical stimuli play a critical role in controlling instinctive behaviors.

Ever since a pheromone secreted by a female moth that attracts males was first identified in 1959, researchers have identified many chemicals that affect behavior in a wide variety of animal species, from insects to mammals to humans.

However, despite this growing list of known pheromones, researchers know little about the mechanism behind how pheromones actually work.

'It is widely known that some chemicals, especially odors, can impact an animal's instinctive behaviors even on first contact,' says Dr Kazushige Touhara, a professor at the University of Tokyo's Graduate School of Agricultural and Life Sciences, who supervised the study.

To learn more about pheromone function in mice, the researchers experimented with a male pheromone called ESP1 secreted from the tear gland.

The pheromone, called ESP1, has been shown to enhance sexual behaviors in females, but elicit aggressive behaviors in males exposed to the pheromone along with unfamiliar male urine.

The researchers studied the pheromone's mode of action by infecting the receptor neural circuit with a virus, and labeling the infected cells with a fluorescent protein to vizualize how it spread.

By using this method, the researchers found that ESP1 was routed differently in the brains of males and females, by neurons in a region of the brain called the amygdala.

To learn more about pheromone function in mice, the researchers experimented with a male pheromone secreted from the tear gland.

The pheromone, called ESP1, has been shown to enhance sexual behaviors in females, but elicit aggressive behaviors in males exposed to the pheromone along with unfamiliar male urine.

ESP1 was less complex to study than other pheromones because it is a single purified chemical that is detected by a sole corresponding receptor, making it comparatively easier to track than most pheromones which tend to be composed of many different substances.

The researchers studied the pheromone's mode of action by infecting the receptor neural circuit with a virus, and labeling the infected cells with a fluorescent protein to vizualize how it spread.

This provided an image of nerve fibers belonging to specific neurons in the brain, and synapses relaying impulses from neuron to neuron, mapping the foundation that conveys ESP1 signals in the brain.

By using this method, the researchers found that ESP1 was routed differently in the brains of males and females, by neurons in a region of the brain called the amygdala.

The researchers also found that the activation of neurons that respond to the pheromone in the region of the brain called the hypothalamus enhanced sexual behavior in female mice - even in the absence of actual ESP-1.

The researcher did this by using tools to selectively manipulate neurons responding to a particular stimulus.

By contrast, the activation of neurons that respond to snake skin - a predator cue that elicits defensive behaviors - in the same brain area showed no change in sexual behaviors.

'This finding suggests that there are two different types of neurons, ESP1 and predator neurons, and only the former controls sexual behaviors in female mice,' Dr Touhara said.

A different study showed a similar discovery in fruit flies.

It showed that a particular sex pheromone enhances female sexual behaviors and male aggression via separate neural circuits between the sexes.

This suggests that a sexually distinct circuit may be a universal strategy for converting male pheromone information into appropriate behavioral output.

The researchers say that further study into the neural basis underlying female sexual behaviors could help provide insight into the origins of sexual dysfunctions.

 

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