Time to sleep? Or is there something more interesting to do? Image supplied by Machado, Afonso et al. (CC BY 4.0)

Sleep or sex?

Male fruit flies have competing drives to mate and sleep.

Most people sleep for around seven or eight hours at night, but if there is something important or interesting to do — for example, taking care of a baby, finishing a task before a deadline, or watching an entertaining movie — we may stay up late. In other words, sleep is regulated by motivational states. The drive to sleep accumulates during wakefulness and decreases during sleep. Thus sleep and other motivational drives compete to decide whether we sleep or engage in other important or interesting activities.

The idea that sleep and sex drives might compete with each other is intuitive, but had not been studied experimentally. Daniel Machado, Dinis Afonso and co-workers have now studied how this competition determines the behavior of male fruit flies. The presence of a female fly usually keeps a male fly awake at night. However, a male that has recently mated several times (and has low sex drive) or one that was sleep deprived (and has high sleep drive) ignores the female and goes to sleep.

Further investigation revealed a small number of previously unknown neurons (termed MS1) are required for sexual arousal to overcome the male’s desire to sleep. These neurons do not belong to a circuit that is known to be important for male sexual behavior, but they do communicate with that circuit using a neurotransmitter called octopamine. This communication suppresses sleep and promotes courtship.

The next steps will be to identify the specific neurons that communicate directly with the MS1 neurons and to determine whether MS1 neurons have a direct role in regulating sex drive. Investigating these details will help us to understand more generally how competing drives influence behavioral choices.

To find out more

Read the eLife research paper on which this eLife digest is based: “Identification of octopaminergic neurons that modulate sleep suppression by male sex drive” (May 16, 2017).
eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.
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