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updated 12/1/2011 4:20:39 PM ET 2011-12-01T21:20:39

The uproar that followed a November episode of Fox's "Glee" in which two teen couples had sex for the first time may have some scientific legs. New research shows sex during the adolescent years could affect mood and brain development into adulthood. 

The study, which was carried out on hamsters, reveals how social experiences during adolescence when the brain is still developing can have broad consequences, say the researchers from Ohio State University College of Medicine.

Specifically, the animals that mated earlier in life had higher levels of depressive behaviors, changes to the brain and smaller reproductive tissues compared to those that had intercourse later or not at all.

"Having a sexual experience during this time point, early in life, is not without consequence," study co-author John Morris, a doctoral student in psychology at Ohio State, said in a statement.

Morris and his colleagues cautioned, however, that the study should not be used to promote teenage abstinence, as they noted the research was carried out on hamsters and it isn't certain the same conclusion will hold for humans. As such, more research is needed understand the effects of sex during puberty.

The study, which was presented on Nov. 15 at the Society for Neuroscience annual meeting, has yet to be peer-reviewed for acceptance in a scientific journal.

Testing the effects of sex

The researchers had a group of 40-day-old male hamsters (the equivalent of human teens) mate with adult females in heat. A second group of males mated in adulthood (80 days into life), while a control group was not exposed to females. Hamsters reach puberty at 21 days, and by 40 days have reached late- to post-adolescence, roughly equivalent to ages 16 to 20 in humans, said study researcher Randy Nelson, neuroscience professor and chair at Ohio State.

Researchers did various tests on the hamsters at 120 days.

When placed in water, the animals that had sex at 40 days were more likely to stop swimming vigorously, a symptom of depression, than the other three groups. All of the sexually active hamsters showed higher levels of anxiety, measured by willingness to explore a maze, than the virgin hamsters.

The group that had sex in adolescence also showed less complexity in the brain's dendrites, thebranching extensions of neurons that receive messages from other nerve cells, and higher expression of a gene associated with inflammation. Certain reproductive tissues, including the seminal vesicles (glands in males that secrete ejaculate) and vas deferens (tube that carries sperm out of the testes), were also smaller in these animals. [ 5 Myths About the Male Body ]

The 40-day group also showed some benefits of early life sexual experience, the researchers said, including reduced body mass and enhanced immune responses in adulthood.

Hormones plus experience

"We used the opportunity to have sex, which naturally increases testosterone levels, to see whether these experiences during early life would have long-term consequence," co-author Zachary Weil, a research assistant professor of neuroscience at Ohio State, told LiveScience. "Previous animal studies have shown that experiences and sex hormones when administered early in life have long-term consequences for physiology, brain and behavior."

The researchers based their study on work by Cheryl Sisk at Michigan State University that showed that, in rodents, the elevated testosterone levels in puberty influence the development of brain circuits that underlie male social behaviors. In Sisk's study, castrated hamsters were less likely to mate with receptive females and were more submissive toward male intruders compared with males that had natural levels of testosterone. Replacing the hormone in adulthood did not restore normal levels of these social behaviors.

"We think that pubertal testosterone organizes neural circuits during adolescence in a way that maximizes male-typical social responses and behaviors in adulthood," said Sisk, who was not involved in the current study. She added that testosterone may be linked to structural changes in the brain, including how the dendrites are organized or connected to one another.

Weil's team is now researching whether testosterone is the sole mechanism. In a new study, the animals will be given the hormone rather than allowed to mate.

Sisk said she believes that a combination of hormones and experiences affect brain development during puberty and adolescence. "In humans, these two variables are hard to tease apart, because the elevated hormone levels that are typical of puberty lead to the appearance of secondary sex characteristics, which in turn changes the nature of interactions with parents, peers and teachers," she said.

Implications for teen sex

In response to the "virgin sex" on "Glee," the Parents Television Council, a watchdog group, denounced the episode in a statement before it aired, saying,"The fact that 'Glee' intends to ... celebrate children having sex is reprehensible." While the new study can't argue for or against this statement, its results suggest more discussion is needed on how early experiences impact adulthood, the researchers say.

"These results are very preliminary and should be used only to stimulate discussion about the role of early life experiences in humans in a general way," Weil said.

Thirteen percent of 15-year-olds in the U.S. have had heterosexual sex, according to the Centers for Disease Control and Prevention, and the average age for first-time intercourse is 17 — well within the equivalent age for the new study. "There is previous evidence that the age of first sexual experiences correlates with mental health issues in humans," Weil said. "But with all human research, there are a number of other variables involved, such as parental supervision and socioeconomic status, that may be involved with both the age of first experience and depression." [ 10 Surprising Sex Statistics ]

Although his team's work may be useful in beginning to understand the physical and mental health outcomes of adolescent sex in humans, Weil said the key finding of the study is that experience during adolescence, when the brain is still developing, can have long-term effects on health and behavior. He cautioned against direct correlations with humans.

"In no way do these data bear directly on the issue of teenage abstinence," Weil stressed. "Much more research needs to be done in both human and animal models to understand how these types of experiences translate into changes in mood and physiology."

Weil said the data does, however, indicate how potentially damaging neglect and abuse of young people can be, in which both heightened hormones and negative experiences are at work. 

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