#preclinicalstudy — Public Fediverse posts
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DATE: July 28, 2026 at 08:00AM
SOURCE: PSYPOST.ORG** Research quality varies widely from fantastic to small exploratory studies. Please check research methods when conclusions are very important to you. **
-------------------------------------------------TITLE: New study sheds light on how testosterone and estrogen treatments alter sexual motivation
A recent study published in the journal Physiology & Behavior provides evidence that administering opposite-sex hormones to rats tends to shift their sexual behavior and motivation to resemble that of the opposite sex. The findings suggest that these hormonal changes also suppress natural reproductive functioning. This offers new insights into the physiological effects of treatments like gender-affirming hormone therapy.
Cross-sex hormone therapy is commonly prescribed to transgender individuals to help them develop physical characteristics that align with their gender identity. Transgender men may take testosterone to deepen their voices, redistribute body fat, and increase muscle mass. Transgender women might take estrogen to reduce muscle mass, encourage breast growth, and soften their skin. These treatments often yield positive psychological benefits and alleviate feelings of distress related to gender dysphoria.
Along with these physical changes, hormone therapy can affect a person’s sexual functioning and desire in varied ways. Some people report an increase in sexual motivation after beginning treatment, but others experience a loss of desire or difficulties in achieving sexual satisfaction. Because human sexuality is deeply influenced by complex social and cultural factors, studying the direct biological effects of these hormones in humans is difficult.
To better understand the biological mechanisms at play, scientists turn to animal models. Rats are useful for this type of research because their sexual response cycle shares basic biological similarities with human sexual responses. By observing animals, researchers can isolate the effects of hormones on motivation and physical arousal without the influence of human social constructs.
Fay Allison Guarraci, a professor of psychology at Southwestern University in Georgetown, Texas, noticed a gap in this area of study. “I realized that there was very little preclinical work conducted investigating any issues related to transgender health care,” Guarraci said. “Because I study animals, I can model the treatments and various reproductive physiological and behavioral outcomes.”
Personal experiences also inspired her research focus. “I had a friend whose pre-teens was questioning their gender identity and that led them to seek medical care,” Guarraci explained. “The current standard of care is to delay puberty with hormones that block pubertal development (GnRH agonists) to give them more time to consider their gender identity.”
Gonadotropin-releasing hormone (GnRH) agonists are medications used to pause puberty.
“They were delaying pubertal development but there was not much known about how these hormones affect other aspects of their health and behavior beyond development of secondary sex characteristics,” Guarraci said. “Using animal models we could investigate some of the consequences of delaying puberty and following up with transgender hormone therapy if they transition to a gender they were not assigned at birth.”
Guarraci emphasized the clinical need for this data. “I was inspired when I learned that pediatric endocrinologists are desperate for information so they can make informed recommendations to their patients, even if the information is based on animal studies,” she noted.
While her broader research program looks at puberty blockers, the current study focused on adult subjects. Previous research on rats has explored sexual behavior, but most studies used animals that had their reproductive organs surgically removed. To address these gaps in the medical literature, the current research models how prolonged exposure to opposite-sex hormones interacts with natural hormone production and affects sexual motivation in intact adult subjects.
To conduct the experiment, the researchers utilized sexually experienced adult Long-Evans rats. The animals were considered gonadally intact, meaning they had not been surgically altered to remove their natural reproductive organs, such as ovaries in females or testes in males. The study included an initial sample of sixteen female rats and eighteen male rats.
The scientists randomly assigned the female rats to receive either a specific type of testosterone or a placebo made of sesame oil. The testosterone was given via injection twice a week for five weeks to mimic the ongoing hormone treatment prescribed to transgender men. One female rat from the control group was later excluded from the analysis because she did not display sexual receptivity during testing, leaving fifteen female rats in the final data set.
For the male rats, the scientists randomly assigned them to receive either daily injections of an estrogen compound or a sesame oil placebo for twenty-eight consecutive days. This schedule was chosen to model the continuous estrogen therapy commonly prescribed to transgender women. During the treatment period, all animals were weighed regularly and housed with same-sex cage mates in a controlled environment.
On the final day of the hormone treatments, the researchers evaluated the sexual motivation of the subjects using a partner preference test. The testing apparatus was a large plastic enclosure divided into three distinct sections. During the first phase of the test, known as the no-contact phase, the subject rat was placed in the middle section. A female stimulus rat was placed in one outer section, and a male stimulus rat was placed in the other.
Wire mesh barriers separated the middle section from the outer areas. This allowed the subject rat to see, hear, and smell the stimulus animals without being able to physically interact with them. For ten minutes, trained observers recorded how much time the subject spent near each stimulus animal and how many times they visited the barriers.
Following the no-contact phase, the scientists immediately initiated a contact phase. They removed the wire mesh barriers, allowing the subject rat to move freely throughout the entire enclosure and interact physically with both the male and female stimulus rats. During this ten-minute period, the researchers closely monitored and recorded the exact timing and types of sexual behaviors displayed.
In female rats, the testosterone treatment appeared to alter their natural sexual preferences. Typically, female rats prefer to spend more time near a male when a physical barrier is present, as this allows them to control the pace of the sexual encounter safely. However, the female rats treated with testosterone spent significantly less time near the male stimulus during the no-contact phase compared to the control group.
During the contact phase, the testosterone-treated females spent less time with the female stimulus animal and visited her less often than the control rats did. The authors noted that this shift in behavior resembles a more masculine pattern of sexual preference.
“Our paradigm allowed us to see who the rats ‘wanted’ to spend time with when they could pick between either a social partner (same sex) or a sexual partner (opposite sex),” Guarraci told PsyPost. “We found that females showed preferences that were more similar to male rats, but they did not display male sexual stimulations (mounts), which we thought might happen.”
In addition to these changes in preference, the female rats given testosterone displayed fewer solicitation behaviors. Solicitation behaviors are specific physical movements, such as hopping or wiggling their ears, that female rats use to signal sexual interest to males.
The testosterone treatment also affected the female rats’ reproductive physiology. The researchers tracked the female animals’ natural reproductive cycles, known as estrous cycles, by examining their cells under a microscope. The females receiving testosterone experienced disrupted cycles and spent fewer days in the fertile phases compared to the control group. They also gained more body weight and developed smaller ovaries, which suggests that the testosterone suppressed their natural ovarian function.
Despite this suppression, the females still displayed some typical mating behaviors, which stood out to the researchers. “I was surprised that testosterone enanthate (TE) disrupted their reproductive estrous cycle (changes in hormones and ovulation, like the menstrual cycle in women), but they were still able to show behavior typical at ovulation even though they were not ovulating,” Guarraci said.
“In female rats, like most mammals, sexual behavior (willingness to mate) is tightly linked to ovulation,” she continued. “This finding indicated to me that sexual behavior is likely being influenced by aromatization (conversion) of TE into estrogen and its activation of the brain to produce sexual behavior, in the absence of ovulation.”
“Even more interestingly, the behavior of TE treated females was not identical to females who were ‘ovulating’ (i.e., given hormones to mimic ovulation behavior),” Guarraci noted. “It was not totally masculinized but it shared characteristics of male sexual behavior and female sexual behavior.”
The estrogen treatment produced noticeable behavioral changes in the male rats as well. Ordinarily, male rats show a strong preference for spending time with a female partner when physical contact is allowed. However, the male rats treated with estrogen spent significantly more time with the male stimulus animal and less time with the female stimulus animal during the unrestricted contact phase.
The researchers observed that the estrogen-treated males exhibited a more feminine pattern of sexual preference. When physical contact was permitted, they seemed less interested in a sexual partner and more interested in a non-sexual partner. The estrogen treatment also affected their physical mating behaviors. The males receiving estrogen initiated fewer sexual mounts and took a significantly longer time to attempt their first mount compared to the male control group.
Physiologically, the continuous estrogen exposure suppressed the natural reproductive functions of the male subjects. By the end of the twenty-eight-day treatment period, the male rats in the estrogen group had gained less body weight than the control rats. Additionally, their testes were significantly smaller in proportion to their body weight, providing evidence that the estrogen treatment reduced their natural testicular activity.
“Motivation to mate is powerful and influenced by prenatal and neonatal (just after birth) hormone exposure,” Guarraci said of the overall findings. “Our study showed that sexual motivation can be influenced in interesting ways by hormones that are opposite to their endogenous hormones.”
Interpreting animal behavior requires caution, as rats do not experience the social concepts of gender identity or sexual orientation that humans do. Animal models cannot fully capture the nuances of human relationships or the psychological aspects of gender-affirming care.
“Preclinical studies in animal models have an inherent limitation; rats are not people,” Guarraci explained. “Because we are not testing human participants, we can’t directly translate and generalize our findings to people.”
“Although rats and mice are different from humans, we try to study aspects of behavior and physiology that are conserved (similar) across species,” she added. “Female rats and female humans both have reproductive cycles, and both have preferences for opposite-sex partners. Both also are more likely to display sexual behavior around the time of ovulation (just not limited this time in humans).”
The researchers stress that human preferences are influenced by culture and upbringing, so the specific hormonal effects seen in rats may not be identical in humans. Still, the findings provide a window into the biological and physiological shifts that occur when natural hormone levels are altered.
“Animals can be useful in understanding some aspects of reproductive physiology and behavior, when studies in people are not possible,” Guarraci said. “It can give people some heads up about what to expect and what long-term consequences they might have to deal with after they proceed with treatment.”
“Although these treatments are considered ‘safe’, they have not been thoroughly tested in the context that they are being used in,” she noted. “We know that puberty blockers are effective treatments for kids with precocious puberty (signs of pubertal development before the age of 7 or 8 in girls and boys respectively). We know how sex hormones work and affect behavior and physiology when taken as adults if people have hormonal deficiencies (e.g., ‘low T’, menopause).”
“However, we don’t know what happens when you start to take GnRH agonists like leuprolide or Lupron to block puberty at around 10-12 years old,” Guarraci explained. “Kids who are prescribed puberty blockers for precocious puberty typically stop taking the drugs at 12 years old.”
“We also don’t know what the consequences are of taking opposite-sex hormones during this period of development; these hormones are not congruent with their endogenous gonadal hormones,” she added. “So my research over the past five years has been investigating these topics.”
In future projects, the research team plans to explore those exact developmental questions. “We are hoping to continue on this research to assess the long-term effects of puberty blockers and cross-sex hormones on changes in the brain and in the genitals to understand physical issues that arise from delaying puberty and then taking hormones that do not align with gender assigned at birth,” Guarraci said.
“Specifically, we are interested in how the brain develops under these conditions to better understand potential effects on emotional, social, sexual, and cognitive development,” she added. “We also want to know if the effects on brain development that are affected by hormones are permanent or transient.”
The study, “Chronic testosterone enanthate or estradiol benzoate affects sexual behavior and motivation in Long-Evans rats tested for partner preference,” was authored by Raylee G. Bowling, Chance T. Bauer, Iva Irabor-Ighedosa, Kole M. Petersen, Katarina Wilson, Anna Pavlova, Alex Avila, Sarah H. Meerts, and Fay A. Guarraci.
-------------------------------------------------
Private, vetted email list for mental health professionals: https://www.clinicians-exchange.org
Unofficial Psychology Today Xitter to toot feed at Psych Today Unofficial Bot @PTUnofficialBot
-------------------------------------------------
#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #CrossSexHormones #SexualMotivation #GenderAffirmingCare #HormoneTherapyResearch #PreclinicalStudy #TransHealthScience #SexualBehavior #GnRHBlockers #PubertyBlockers #HormoneImpactOnBehavior
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DATE: July 28, 2026 at 08:00AM
SOURCE: PSYPOST.ORG** Research quality varies widely from fantastic to small exploratory studies. Please check research methods when conclusions are very important to you. **
-------------------------------------------------TITLE: New study sheds light on how testosterone and estrogen treatments alter sexual motivation
A recent study published in the journal Physiology & Behavior provides evidence that administering opposite-sex hormones to rats tends to shift their sexual behavior and motivation to resemble that of the opposite sex. The findings suggest that these hormonal changes also suppress natural reproductive functioning. This offers new insights into the physiological effects of treatments like gender-affirming hormone therapy.
Cross-sex hormone therapy is commonly prescribed to transgender individuals to help them develop physical characteristics that align with their gender identity. Transgender men may take testosterone to deepen their voices, redistribute body fat, and increase muscle mass. Transgender women might take estrogen to reduce muscle mass, encourage breast growth, and soften their skin. These treatments often yield positive psychological benefits and alleviate feelings of distress related to gender dysphoria.
Along with these physical changes, hormone therapy can affect a person’s sexual functioning and desire in varied ways. Some people report an increase in sexual motivation after beginning treatment, but others experience a loss of desire or difficulties in achieving sexual satisfaction. Because human sexuality is deeply influenced by complex social and cultural factors, studying the direct biological effects of these hormones in humans is difficult.
To better understand the biological mechanisms at play, scientists turn to animal models. Rats are useful for this type of research because their sexual response cycle shares basic biological similarities with human sexual responses. By observing animals, researchers can isolate the effects of hormones on motivation and physical arousal without the influence of human social constructs.
Fay Allison Guarraci, a professor of psychology at Southwestern University in Georgetown, Texas, noticed a gap in this area of study. “I realized that there was very little preclinical work conducted investigating any issues related to transgender health care,” Guarraci said. “Because I study animals, I can model the treatments and various reproductive physiological and behavioral outcomes.”
Personal experiences also inspired her research focus. “I had a friend whose pre-teens was questioning their gender identity and that led them to seek medical care,” Guarraci explained. “The current standard of care is to delay puberty with hormones that block pubertal development (GnRH agonists) to give them more time to consider their gender identity.”
Gonadotropin-releasing hormone (GnRH) agonists are medications used to pause puberty.
“They were delaying pubertal development but there was not much known about how these hormones affect other aspects of their health and behavior beyond development of secondary sex characteristics,” Guarraci said. “Using animal models we could investigate some of the consequences of delaying puberty and following up with transgender hormone therapy if they transition to a gender they were not assigned at birth.”
Guarraci emphasized the clinical need for this data. “I was inspired when I learned that pediatric endocrinologists are desperate for information so they can make informed recommendations to their patients, even if the information is based on animal studies,” she noted.
While her broader research program looks at puberty blockers, the current study focused on adult subjects. Previous research on rats has explored sexual behavior, but most studies used animals that had their reproductive organs surgically removed. To address these gaps in the medical literature, the current research models how prolonged exposure to opposite-sex hormones interacts with natural hormone production and affects sexual motivation in intact adult subjects.
To conduct the experiment, the researchers utilized sexually experienced adult Long-Evans rats. The animals were considered gonadally intact, meaning they had not been surgically altered to remove their natural reproductive organs, such as ovaries in females or testes in males. The study included an initial sample of sixteen female rats and eighteen male rats.
The scientists randomly assigned the female rats to receive either a specific type of testosterone or a placebo made of sesame oil. The testosterone was given via injection twice a week for five weeks to mimic the ongoing hormone treatment prescribed to transgender men. One female rat from the control group was later excluded from the analysis because she did not display sexual receptivity during testing, leaving fifteen female rats in the final data set.
For the male rats, the scientists randomly assigned them to receive either daily injections of an estrogen compound or a sesame oil placebo for twenty-eight consecutive days. This schedule was chosen to model the continuous estrogen therapy commonly prescribed to transgender women. During the treatment period, all animals were weighed regularly and housed with same-sex cage mates in a controlled environment.
On the final day of the hormone treatments, the researchers evaluated the sexual motivation of the subjects using a partner preference test. The testing apparatus was a large plastic enclosure divided into three distinct sections. During the first phase of the test, known as the no-contact phase, the subject rat was placed in the middle section. A female stimulus rat was placed in one outer section, and a male stimulus rat was placed in the other.
Wire mesh barriers separated the middle section from the outer areas. This allowed the subject rat to see, hear, and smell the stimulus animals without being able to physically interact with them. For ten minutes, trained observers recorded how much time the subject spent near each stimulus animal and how many times they visited the barriers.
Following the no-contact phase, the scientists immediately initiated a contact phase. They removed the wire mesh barriers, allowing the subject rat to move freely throughout the entire enclosure and interact physically with both the male and female stimulus rats. During this ten-minute period, the researchers closely monitored and recorded the exact timing and types of sexual behaviors displayed.
In female rats, the testosterone treatment appeared to alter their natural sexual preferences. Typically, female rats prefer to spend more time near a male when a physical barrier is present, as this allows them to control the pace of the sexual encounter safely. However, the female rats treated with testosterone spent significantly less time near the male stimulus during the no-contact phase compared to the control group.
During the contact phase, the testosterone-treated females spent less time with the female stimulus animal and visited her less often than the control rats did. The authors noted that this shift in behavior resembles a more masculine pattern of sexual preference.
“Our paradigm allowed us to see who the rats ‘wanted’ to spend time with when they could pick between either a social partner (same sex) or a sexual partner (opposite sex),” Guarraci told PsyPost. “We found that females showed preferences that were more similar to male rats, but they did not display male sexual stimulations (mounts), which we thought might happen.”
In addition to these changes in preference, the female rats given testosterone displayed fewer solicitation behaviors. Solicitation behaviors are specific physical movements, such as hopping or wiggling their ears, that female rats use to signal sexual interest to males.
The testosterone treatment also affected the female rats’ reproductive physiology. The researchers tracked the female animals’ natural reproductive cycles, known as estrous cycles, by examining their cells under a microscope. The females receiving testosterone experienced disrupted cycles and spent fewer days in the fertile phases compared to the control group. They also gained more body weight and developed smaller ovaries, which suggests that the testosterone suppressed their natural ovarian function.
Despite this suppression, the females still displayed some typical mating behaviors, which stood out to the researchers. “I was surprised that testosterone enanthate (TE) disrupted their reproductive estrous cycle (changes in hormones and ovulation, like the menstrual cycle in women), but they were still able to show behavior typical at ovulation even though they were not ovulating,” Guarraci said.
“In female rats, like most mammals, sexual behavior (willingness to mate) is tightly linked to ovulation,” she continued. “This finding indicated to me that sexual behavior is likely being influenced by aromatization (conversion) of TE into estrogen and its activation of the brain to produce sexual behavior, in the absence of ovulation.”
“Even more interestingly, the behavior of TE treated females was not identical to females who were ‘ovulating’ (i.e., given hormones to mimic ovulation behavior),” Guarraci noted. “It was not totally masculinized but it shared characteristics of male sexual behavior and female sexual behavior.”
The estrogen treatment produced noticeable behavioral changes in the male rats as well. Ordinarily, male rats show a strong preference for spending time with a female partner when physical contact is allowed. However, the male rats treated with estrogen spent significantly more time with the male stimulus animal and less time with the female stimulus animal during the unrestricted contact phase.
The researchers observed that the estrogen-treated males exhibited a more feminine pattern of sexual preference. When physical contact was permitted, they seemed less interested in a sexual partner and more interested in a non-sexual partner. The estrogen treatment also affected their physical mating behaviors. The males receiving estrogen initiated fewer sexual mounts and took a significantly longer time to attempt their first mount compared to the male control group.
Physiologically, the continuous estrogen exposure suppressed the natural reproductive functions of the male subjects. By the end of the twenty-eight-day treatment period, the male rats in the estrogen group had gained less body weight than the control rats. Additionally, their testes were significantly smaller in proportion to their body weight, providing evidence that the estrogen treatment reduced their natural testicular activity.
“Motivation to mate is powerful and influenced by prenatal and neonatal (just after birth) hormone exposure,” Guarraci said of the overall findings. “Our study showed that sexual motivation can be influenced in interesting ways by hormones that are opposite to their endogenous hormones.”
Interpreting animal behavior requires caution, as rats do not experience the social concepts of gender identity or sexual orientation that humans do. Animal models cannot fully capture the nuances of human relationships or the psychological aspects of gender-affirming care.
“Preclinical studies in animal models have an inherent limitation; rats are not people,” Guarraci explained. “Because we are not testing human participants, we can’t directly translate and generalize our findings to people.”
“Although rats and mice are different from humans, we try to study aspects of behavior and physiology that are conserved (similar) across species,” she added. “Female rats and female humans both have reproductive cycles, and both have preferences for opposite-sex partners. Both also are more likely to display sexual behavior around the time of ovulation (just not limited this time in humans).”
The researchers stress that human preferences are influenced by culture and upbringing, so the specific hormonal effects seen in rats may not be identical in humans. Still, the findings provide a window into the biological and physiological shifts that occur when natural hormone levels are altered.
“Animals can be useful in understanding some aspects of reproductive physiology and behavior, when studies in people are not possible,” Guarraci said. “It can give people some heads up about what to expect and what long-term consequences they might have to deal with after they proceed with treatment.”
“Although these treatments are considered ‘safe’, they have not been thoroughly tested in the context that they are being used in,” she noted. “We know that puberty blockers are effective treatments for kids with precocious puberty (signs of pubertal development before the age of 7 or 8 in girls and boys respectively). We know how sex hormones work and affect behavior and physiology when taken as adults if people have hormonal deficiencies (e.g., ‘low T’, menopause).”
“However, we don’t know what happens when you start to take GnRH agonists like leuprolide or Lupron to block puberty at around 10-12 years old,” Guarraci explained. “Kids who are prescribed puberty blockers for precocious puberty typically stop taking the drugs at 12 years old.”
“We also don’t know what the consequences are of taking opposite-sex hormones during this period of development; these hormones are not congruent with their endogenous gonadal hormones,” she added. “So my research over the past five years has been investigating these topics.”
In future projects, the research team plans to explore those exact developmental questions. “We are hoping to continue on this research to assess the long-term effects of puberty blockers and cross-sex hormones on changes in the brain and in the genitals to understand physical issues that arise from delaying puberty and then taking hormones that do not align with gender assigned at birth,” Guarraci said.
“Specifically, we are interested in how the brain develops under these conditions to better understand potential effects on emotional, social, sexual, and cognitive development,” she added. “We also want to know if the effects on brain development that are affected by hormones are permanent or transient.”
The study, “Chronic testosterone enanthate or estradiol benzoate affects sexual behavior and motivation in Long-Evans rats tested for partner preference,” was authored by Raylee G. Bowling, Chance T. Bauer, Iva Irabor-Ighedosa, Kole M. Petersen, Katarina Wilson, Anna Pavlova, Alex Avila, Sarah H. Meerts, and Fay A. Guarraci.
-------------------------------------------------
Private, vetted email list for mental health professionals: https://www.clinicians-exchange.org
Unofficial Psychology Today Xitter to toot feed at Psych Today Unofficial Bot @PTUnofficialBot
-------------------------------------------------
#psychology #counseling #socialwork #psychotherapy @psychotherapist @psychotherapists @psychology @socialpsych @socialwork @psychiatry #mentalhealth #psychiatry #healthcare #depression #psychotherapist #CrossSexHormones #SexualMotivation #GenderAffirmingCare #HormoneTherapyResearch #PreclinicalStudy #TransHealthScience #SexualBehavior #GnRHBlockers #PubertyBlockers #HormoneImpactOnBehavior