Scientists have discovered a biological trigger for early puberty

A new study from Branhouse's lab has shown how early childhood adversity triggers early puberty and anxiety in later life, opening the door to potential interventions.

The age of onset of puberty has been falling for decades.

In the United States, the average age of puberty onset for girls ranges from 8.8 to 10.3 years. Early puberty onset, which is associated with many health risks, may be caused by chronic stress in children.

A new study by Northeastern University researchers, published in the journal Hormones and Behavior, is the first to find that early childhood stress affects a part of the brain — specifically, a protein in the cell membrane — responsible for preventing the early onset of puberty.

A receptor in the brain may suppress the release of hormones or "put the brakes" on early puberty. The receptor stops functioning normally under chronic stress, triggering a cascade of signals that leads to the early onset of puberty, according to researchers at Northeastern University.

Children who experience early puberty are at risk for developing reproductive cancers, metabolic syndromes such as diabetes, cardiovascular disease, and emotional and social problems in adulthood, according to research.

The researchers hope their findings will lead to the creation of medical interventions in the future.

"Early puberty is important because it seems to be associated with psychopathologies later in life, such as anxiety disorders," says Heather Branhouse, a professor of psychology at Northeastern University. "Physiological medical conditions may also be associated with early puberty."

The biological mechanism by which early childhood stress leads to early puberty has remained largely unknown, Branhaus notes.

A new study from Branhouse's lab at Northeastern University has identified a receptor — the part of a brain cell that receives messages from another cell — in the hypothalamus, a region of the brain that controls many bodily functions through hormones.

From previous research, scientists knew that precocious puberty in girls is associated with early adversity and that early puberty predicts anxiety in adolescence and adulthood.

They set out to confirm these findings and identify the biological trigger for early puberty in the brain.

Lauren Granata, a Northeastern University graduate with a PhD in psychology, co-authored the study and conducted the research on animal models. The idea that stress triggers puberty initially seemed counterintuitive to her.

"It's well known now that stress suppresses reproduction," Granata says. "I thought there was a lot of opportunity to learn something new."

The scientists first confirmed the hypothesis that early childhood adversity does indeed cause early puberty in rats. Working with an animal model, Granata says, allowed them to isolate one specific factor—a disrupted relationship with the mother—aside from other factors such as nutrition.

Of course, Granata adds, what happens in humans doesn't always directly correlate with the animal model, but it's good evidence that dysfunctional maternal care in early life may be one factor regulating early puberty.

"The way you can really traumatize a child or a developing rodent is through manipulation and disruption of the caregiver relationship," says Branhouse.

Other adverse childhood experiences people may experience include neglect, lack of resources and abuse, she adds.

To find a biomarker, a biological molecule in the brain whose condition indicates early or normal puberty, Granata looked at the hypothalamus, as it is widely known to control when a person will go through puberty, among other important functions.

"There are cells that become activated and release certain proteins and peptides [hormones] that initiate puberty," Branhouse says.

Granata found that these brain cells actually begin expressing and releasing these proteins earlier in female rats that were separated from their mothers. She identified a specific receptor, CRH-R1, in the hypothalamus that suppresses prepuberty and is affected by chronic stress.

"You can think of it as a constant battle between the 'go' signal and the 'stop' signal [in the brain]," Granata says.

Stress hormones typically act as "brakes" on puberty because they cause the CRH-R1 receptor to suppress the release of hormones needed for puberty. So they hypothesized that it was not a single stressful event but chronic stress that weakened the "brakes" on puberty, or made the receptor less sensitive to stress hormones.

This triggers a cascade of signals in the brain and body.

"Now all the 'go' signals are given free rein and say, 'It's time for puberty,'" Granata says.

The hypothalamus releases specific hormones that tell the system to release the brakes and produce estrogen and testosterone, which are involved in the growth and maintenance of reproductive tissues.

Scientists did not observe accelerated puberty in male rats who were also separated from their mothers.

To study the links between adversity and childhood trauma and anxiety in adolescents and adults, the researchers used acoustic startle—noise bursts that interrupt background white noise—in post-pubertal female rats. The experiment showed a significant negative correlation between age at puberty and the magnitude of the acoustic startle response, which is associated with disorders.

The rat that had earlier puberty, Granata says, experienced higher levels of anxiety as a teenager.

She hopes these findings can be used to potentially create interventions and treatments for girls who are at higher risk for anxiety and depression in adolescence and adulthood due to early puberty.