'Love hormone' controls sexual behaviour in mice

A small group of neurons that respond to the hormone oxytocin are key to controlling sexual behaviour in mice, a team has discovered.

The researchers switched off these cells which meant they were no longer receptive to oxytocin.

This "love hormone" is already known to be important for many intimate social situations.

Without it, female mice were no more attracted to a mate than to a block of Lego, the team report in journal Cell.

These neurons are situated in the prefrontal cortex, an area of the brain important for personality, learning and social behaviour.

Both when the hormone was withheld and when the cells were silenced, the females lost interest in mating during oestrous, which is when female mice are sexually active.

At other times in their cycle they responded to the males with normal social behaviour.

The results were "pretty fascinating because it was a small population of cells that had such a specific effect", said co-author of the work Nathaniel Heintz of the Rockefeller University in New York.

"This internal hormone gets regulated in many different contexts; in this particular context, it works through the prefrontal cortex to help modulate social and sexual behaviour in female mice.

"It doesn't mean it's uniquely responsible because the hormone acts in several important places in the brain but it does show that this particular cell type is required for this aspect of female social behaviour," Dr Heintz told BBC News.

To silence the neurons, the team used toxins that block the ability of the cells to transmit signals to other neurons - technology that has recently revolutionised the ability to study small populations of neurons.

"These circuits may exist similarly in other species, including humans, so understanding these circuits we found in mice might help us to understand why oxytocin has these effects in humans, too," Dr Heintz added.

The researchers also discovered that female cells were more responsive to the hormone than the equivalent cells in male mice.

Gareth Leng, professor of experimental physiology at the University of Edinburgh, UK, who was not involved with the study, said that the work was very interesting and added to a body of knowledge showing that oxytocin receptors are situated at many parts of the brain, facilitating social interactions.

"Oxytocin seems to be able to alter the way that certain groups of neurons talk to each other - effectively rewiring neural circuits - not a physical rewiring, but a functional rewiring."

The study shows more evidence, Prof Leng added, that oxytocin "has very widespread actions at many different brain sites".

"Oxytocin seems to be acting not like a conventional neurotransmitter, but more like a hormone within the brain itself," he told BBC News.

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