A man rests his head on a woman's shoulder with her back facing the cameraShare on Pinterest
Testosterone does not only promote aggressiveness, an animal study finds. Uwe Krejci/Getty Images
  • Researchers investigated the effects of testosterone on prosocial behaviors in male gerbils.
  • They found that testosterone both increased and decreased prosocial behavior depending on context.
  • The researchers say that further work is needed to understand the context-specific effects of testosterone.

Behavioral shifts are vital for adapting to dynamic social environments and for survival and fitness among most organisms. Hormone systems play a particularly significant role in adaptability.

Testosterone (T) increases response to sexual and aggressive stimuli. Although human studies show that T can promote positive social responses in some contexts—such as promoting social status—its influence on prosocial, nonsexual behavior in animals remains largely unexplored.

How T affects prosocial responses in the same individual in different social contexts also remains largely unknown.

Recently, researchers investigated how T influences prosocial behavior in male Mongolian gerbils across different social contexts.

They found that T’s effects varied according to social context. They also found that testosterone production affected oxytocin signaling mechanisms.

“It is extremely important to elucidate how neuromodulators that we canonically put into categories like ‘love hormone’ or ‘aggression hormone’ interact to optimize how we navigate the world,” Dr. Bianca Jones Marlin, assistant professor of cell research at the Zuckerman Institute at Columbia University, who was not involved in the study, told Medical News Today.

“Exploring testosterone in affiliative social interactions gives us insight into the vast role that neuromodulators can play beyond these historic groupings. For instance, testosterone’s ability to increase oxytocin may be one of the key ways that we are able to switch from aggression to prosocial behavior,” she added.

“The next question in this field will be to answer how these neuromodulators interact with one another, how these interactions affect the brain, and how those effects ultimately impact the animal’s behaviors,” she noted.

The study was published in the journal Proceedings of the Royal Society B.

Mongolian gerbils are monogamous animals that are known to form lifelong pair bonds. For the study, the researchers obtained 14 adult male gerbils and 14 female gerbils.

After pairing them together and ensuring pair bonds were established, they injected the male gerbils with either testosterone or a placebo saline solution.

The researchers noted that within 30 minutes, testosterone injections increased ‘cuddly’ behavior compared to gerbils who received the saline solution.

They further noted that T promoted nonsexual prosocial responses to female partners, as they did not observe any mounting or ‘foot-stomping,’ which is typically exhibited when a female is sexually receptive.

Male gerbils injected with testosterone also exhibited more oxytocin activity in their brains while interacting with their partners than males injected with saline.

A week later, the researchers removed females from the cages and observed how the males behaved when confronted with a male intruder.

When confronted with an intruder, male gerbils typically chase or avoid them. In this instance, the researchers noted that male gerbils injected with testosterone became ‘friendly’ with intruders.

When injected with a second dose of testosterone, however, they suddenly became more aggressive.

When asked how T may enhance context-appropriate behavior, Dr. Aubrey Kelly, assistant professor at the Department of Psychology at Emory University, and lead author of the study, told MNT that while further research is needed to understand the biological underpinnings, there are several possible explanations.

“T could make individuals more aware of their immediate surroundings by acting on chemicals in the brain [such as] oxytocin that are known to enhance attention to social cues. Generally, hormones can act as state enhancers—in this case, T can amplify whatever behaviors might be more likely to occur in certain circumstances.”
— Dr. Aubrey Kelly

“T may also enhance emotional responses, such that T may amplify whatever emotional response may be most appropriate for a given situation. As an example, heart rate is known to increase in response to emotional stimuli, and we know that T can amplify heart rate responses to those stimuli,” Dr. Kelly noted.

“Let’s say you haven’t seen a loved one for a while, and upon being reunited with them, your heart rate increases at the sight of them, and you have an emotional response. T may be increasing [simultaneously], and can make that physiological and emotional response stronger,” she added.

When asked the same question, Dr. Roberto Refinetti, professor of psychology and department chair at the University of New Orleans, who was also not involved in the study, told MNT:

“Although testosterone is well known to induce antagonist behavior, it might be more accurate to say that it induces male-specific behavior, with male-specific behavior often—but not always—being antagonist behavior.”

“It is important to note that even neurotransmitters, [whose actions are generally more specific than hormones], are not locked into particular behaviors. They can act on different brain circuits in different ways. Testosterone is not a substance magically acting on a particular brain site to induce aggression. Its action is more complex, or ‘context-dependent’.”
— Dr. Roberto Refinetti

Testosterone and oxytocin

Dr. Robert C. Froemke, Skirball professor of genetics at the Department of Neuroscience and Physiology and professor at the Department of Otolaryngology-Head and Neck Surgery at the New York University Grossman School of Medicine, who was not involved in the study, also told MNT:

“[Research by Prof. Catherine Wolley’s lab at Northwestern University] has indicated that estrogens can rapidly increase brain cell excitability, which would potentially be a mechanism for a steroid hormone [like T] to enhance sensitivity to behavioral context.”

“[It is thus not impossible that] T could do something like this directly, and our group and others—inspired by the Woolley lab’s findings—have reported similar action for oxytocin. Oxytocin can definitely increase sensitivity to social context depending on where and when it acts in the brain, and it’s interesting that the authors report here a big increase in the activity of oxytocin cells,” he added.

The researchers concluded that future research is needed to understand whether T influences behavior via interaction with oxytocin or other hormones.

When asked about the study’s limitations, Dr. Kelly noted that their experiment was conducted on just one species. She added that their results do not explain the long-term effects of T hormonal treatment as they only observed gerbils for a short time.

Dr. Ioana Carcea, assistant professor at the Department of Pharmacology, Physiology, and Neuroscience at Rutgers New Jersey Medical School, who was not involved in the study, told MNT:

“I believe additional experiments will be needed to determine if the increase in oxytocin neuron activity in males results from the surge in testosterone or from heightened prosocial interactions with the partner.”