In a bold decision to correct the skewed sex balance in labs among the scientific fraternity, the US government has announced that it will require all federally-funded researchers to use both male and female animals during experiments.
The US National Institutes of Health supports $30 billion worth of research by 300,000 investigators around the world so this policy will have a huge effect on how science is done, said a report published in the journal Nature.
The NIH is now developing policies that require applicants to report their plans for the balance of male and female cells and animals in preclinical studies in all future applications, unless sex-specific inclusion is unwarranted.
The new policies will be rolled out in phases beginning October 2014.
According to one unpublished survey of 1,200 neuroscience papers from top journals in 2011 and 2012, only 42 percent reported the sex of the animals used.
And when sex was reported, females were only included 24 percent of the time.
These skewed sex balances are likely causing problems for research.
"Researchers using only male animals might miss some of these differences. For instance, a research team that's mainly testing drugs on male animals might miss drugs that could be beneficial to females," it noted.
One example concerns multiple sclerosis (MS). Women are more susceptible to MS than men are but develop less-severe forms of the disease.
The most widely accepted MS animal model has revealed that sex differences in MS are related to both reproductive and non-reproductive factors.
Some Y-chromosome genes (in male mice) seem to have a protective effect against the disease, and some X-chromosome genes (in female mice, with potentially double the dosage) have a disease-causing effect.
"The findings have important implications for other sex-skewed neurological conditions, including Parkinson's disease, schizophrenia and stroke," the report emphasised.
Substance abuse is also affected by sex.
One target for intervention has been stress systems that mediate craving. Female rats exhibit a greater response to stress by the neurotransmitter norepinephrine than do male rats, the report said.
