Washington: The way genes and hormones interact in the brain changes parenting behaviour in mice, a new study including Indian origin researchers has revealed.
Researchers have asserted that our gender differences might be a function of how our brains react to hormones, a new study on mice suggests.
The study showed that when different sex hormones were turned on or off genes in the brain, the mice showed different parenting behaviours.
Though the research was performed in mice, these sex hormones show similar effects in mammals and many of the genes the scientists discovered are found in humans, the researchers say.
It’s possible that hormones are having an effect on brain genes in humans, too, though the behaviours controlled might be different.
“Testosterone and estrogen control sexually dimorphic behaviors in vertebrate species, we’ve known that for a long time that they control behaviors at a very large-scale level,” study researcher Nirao Shah, of the University of California, San Francisco, said.
“What we’ve discovered are [some of] the gene networks that are regulated by these sex hormones.”
The researchers focused on the hypothalamus, a specific region of the adult mouse brain that is involved in mating and parenting behaviours, like courtship, nursing and defending pups. They looked to see what genes were being turned on and off in this region by the presence of sex hormones, such as testosterone, estrogen and progesterone.
They found 16 genes that showed clear sex differences. The researchers then studied four sets of mice that were missing one of these hormone-reactive genes (Brs3, Cckar, Irs4 and Sytl4) to see how their behaviours might change.
The mice all looked normal, but when the researchers studied specific mating and parenting behaviours they found that the mice all had slightly different quirks.
“In each one of these mutants we found deficits in one or another behavior, but everything else appeared untouched, it was normal and looked like the controls did,” Shah said.
“The larger implication of this is that you can take a complex social interaction like mating or fighting and you can sort of break it down into genetically controlled elements of that behavior,” Shah added.
These genes seemed to control male sexual behaviour, male aggression, maternal behaviour and female sexual behaviour in the mice. For example, the female mice missing the gene Cckar had lowered sex drives — about two to three times lower than normal females.
Another gene, Irs4, controlled maternal aggression; female mice missing Irs4 were less aggressive to invaders in their nest and didn``t chase after escaping pups as quickly.
Male mice missing the Tytl4 gene had subtle changes in the pattern of their mating behaviours — they performed their courtship displays in a different order than normal mice, though they still behaved like males and were able to impregnate females.
The other gene they discovered, Brsr3, also controlled male mating behaviours: Males missing the gene initiated sex faster with females and were faster to start fights with other males.
The researchers are looking at the rest of the 16 genes they discovered to determine if they are also regulating certain behaviours. "I suspect there are many more genes like this that are going to be discovered," Shah said.
The study has been published in the journal Cell.