Scientists believe they have found an explanation for female rejection

The research deepens our understanding of how the brain regulates social and reproductive behaviors

A team from the Champalimaud Foundation (a biomedical research institute based in Lisbon, Portugal, which focuses on advanced research and clinical care) has identified a neural circuit critical to sexual rejection, identifying a set of brain cells that play a crucial role in determining whether a woman accepts or rejects mating attempts based on her reproductive cycle. Their findings, published this week in the journal neurondeepen our understanding of how the brain regulates social and reproductive behaviors.

Female mammals, such as rodents, accept mating attempts only during the fertile phase and actively reject males outside of this period. While the areas of the brain that control sexual receptivity are well studied, the mechanisms underlying active rejection are less so.

Susana Lima, senior author and director of the Neuroethology Laboratory of the CF (Champalimaud Foundation), explains that sexual refusal is not just an absence of receptivity, it is an active behavior. Females exhibit defensive actions such as running away, kicking or hitting the male. And that the researchers wanted to understand how the brain transitions between these two drastically different behavioral states.

At the center of the research is the ventromedial hypothalamus (VMH), an evolutionarily ancient brain region that controls social and sexual behavior across species, including humans. Scientists suspect that the VMH may harbor a separate population of cells dedicated to rejection, based on previous low-resolution imaging experiments showing VMH activity during acceptance and rejection of male advances.

The team focused on the anterior VMH, a less explored area, particularly in cells that respond to the hormone progesterone, which fluctuates during the reproductive cycle. “These neurons are ideal for studying how the female brain switches between acceptance and rejection during the cycle,” notes first author Nicolas Gutierrez-Castellanos.

No. Yes. It depends.

Gutierrez-Castellanos says understanding this reversal will provide insight into how the brain integrates signals from the environment and body to shape behavior. For him, this is a striking example of how the same stimulus – in this case, an anxious male – can provoke completely opposite behaviors, depending on the woman’s internal state.

Using advanced techniques such as fiber photometry – which tracks brain activity in real time by measuring calcium signals – the researchers observed the behavior of these progesterone-sensitive neurons in receptive and non-receptive female mice during interactions with males . The results were surprising: Anterior VMH neurons became highly active in non-receptive females, correlating with defensive actions such as kicking and boxing, but were much less active in receptive females.

The researchers said it appears that progesterone-sensitive neurons in the anterior VMH act as gatekeepers to sexual rejection. When a female is outside her fertile window, these neurons become very active, triggering rejection. But during fertility, their activity decreases, allowing mating.

The brain’s dual control knobs

How are these neurons activated or deactivated depending on fertility? To investigate, the team performed electrophysiology experiments, measuring the activity of progesterone-sensitive neurons in brain slices. Gutierrez-Castellanos said they found that in non-receptive women, these neurons received more excitatory signals, making them more likely to fire. “In the receptive women, they received more inhibitory signals, reducing the likelihood of firing. It’s a testament to how adaptable and flexible the neural connections in the hypothalamus and brain can be,” he added.

The activity levels and excitation/inhibition balance of progesterone-sensitive neurons in the anterior VMH strongly suggest their role in sexual rejection. To confirm this, optogenetics was used to selectively activate these neurons with light. In fact, artificially stimulating them during the fertile phase induced rejection behaviors such as kicking and punching. It’s like flipping a switch: Even though the females were fertile, they acted as if they weren’t.

On the other hand, silencing these neurons with a chemical drug in non-receptive females reduced rejection behaviors, although, interestingly, did not make them completely receptive, indicating that two distinct populations of neurons, one controlling rejection and the other receptivity, they work together to produce appropriate behavior based on the female’s internal state.

This setting gives the brain two “knobs” to adjust. This is a more efficient and robust way for the brain to balance these behaviors, ensuring that mating occurs when conception is most likely, while minimizing the risks and costs of mating, such as exposure to predators or disease .

This dual system likely adds flexibility to the brain’s regulation of sexual behavior. Sex is not deterministic. Even during the receptive phase, a female can still reject males, so the ability to tap into both sets of neurons may allow for more nuanced and dynamic behaviors.

Reactive neurons

Notably, these findings are in line with recent research showing that progesterone-sensitive neurons in the posterior VMH, which stimulate sexual receptivity, undergo similar cycle-dependent changes but in the opposite direction: active during the fertile phase and inactive outside of it. of it.

The VMH exists in humans and likely plays similar roles. Recent studies in mouse models have shown that VMH changes in pathological conditions such as polycystic ovary syndrome. Furthermore, socially isolating female mice during development can lead to reduced sexual receptivity, with changes in the same area of ​​the brain, highlighting the clinical relevance of VMH.

“We are only beginning to scratch the surface of how the brain’s internal wiring orchestrates social behavior. There is much more to learn, but these findings bring us one step closer to understanding how neural mechanisms and internal states drive social behavior. complex social interactions, from sexual behavior to aggression and beyond,” concluded Susana.

Source: EurekAlert!

Source: Terra

Ben

Ben Stock is a lifestyle journalist and author at Gossipify. He writes about topics such as health, wellness, travel, food and home decor. He provides practical advice and inspiration to improve well-being, keeps readers up to date with latest lifestyle news and trends, known for his engaging writing style, in-depth analysis and unique perspectives.