Published in Neuron | Estimated reading time: 4 minutes
Deep within the brain’s ventromedial hypothalamus (VMH), a region as ancient as our basic drives, lies a sophisticated neural circuit that determines whether a female mouse will accept or reject potential mates. This circuit, responsive to the hormone progesterone, doesn’t just passively inhibit mating behavior—it actively drives defensive actions like kicking and boxing when females are outside their fertile window.
“Sexual rejection isn’t just the absence of receptivity, it’s an active behavior,” explains Susana Lima, senior author and head of the Neuroethology Lab at the Champalimaud Foundation. This distinction proves crucial for understanding how female mammals navigate reproductive choices.
Using advanced techniques like fiber photometry, which tracks real-time brain activity, the research team observed these neurons spring into action when non-receptive females encountered males. The cells remained notably quiet during fertile periods, effectively operating as a biological switch for rejection behaviors.
Perhaps most compelling was the team’s ability to artificially manipulate these behaviors. When researchers activated these neurons in fertile females using light stimulation (optogenetics), the females began rejecting males despite being in their receptive phase. Conversely, silencing these neurons in non-receptive females reduced rejection behaviors, though it didn’t fully trigger receptivity—suggesting a sophisticated dual-control system in the brain.
“The brain uses two distinct populations of neurons, one controlling rejection and another receptivity, working in concert to produce appropriate behavior,” notes co-first author Basma Husain. “This dual-system likely adds flexibility to the brain’s regulation of sexual behavior, allowing for more nuanced and dynamic responses.”
Key Terms
- Ventromedial Hypothalamus (VMH)
- An evolutionarily ancient brain region that controls social and sexual behavior across species
- Fiber Photometry
- A technique that measures real-time brain activity by tracking calcium signals in neurons
- Optogenetics
- A method that uses light to control neurons that have been genetically modified to be light-sensitive
Test Your Understanding
What makes sexual rejection different from simply not being receptive?
Sexual rejection involves active defensive behaviors like kicking and boxing, rather than just passive non-engagement.
How did researchers prove these neurons control rejection behavior?
They used optogenetics to artificially activate the neurons in fertile females, which caused rejection behaviors even during their typically receptive period.
Why might a dual-control system (separate circuits for rejection and receptivity) be advantageous?
It allows for more flexible and nuanced behavioral responses, as females might need to reject males even during fertile periods based on other factors.
What role does progesterone play in this neural circuit?
The neurons responsible for rejection behavior are responsive to progesterone, which fluctuates throughout the reproductive cycle, helping to coordinate behavior with fertility.
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