Published on: November 16, 2015
by Women’s Brain Health Initaitive:
Twenty years ago, if someone said “women’s health,” it usually meant what is commonly referred to as “bikini medicine”, a term used to account for sex-specific conditions that affect women: breast and ovarian cancers, pregnancy, and menstrual cycles. However, for parts of the body men and women share, such as heart, kidneys and brain, most of the studies were done predominantly on men.
More and more, scientists are realizing that these differences are dangerously understudied and that pervasively and fundamentally, sex matters.
Larry Cahill, a neuroscientist at the University of California Irvine, put it this way in a 2014 interview for 60 Minutes with CBS News reporter Lesley Stahl: “There’s this assumption that you [Lesley] are me [Larry] with pesky hormones. We’re studying all the fundamental things in you without this sort of nuisance stuff; that’s literally an assumption on which all of biological medicine, especially neuroscience, which I know best, has been built.”
Cahill says that even if this view was once defensible, it is no longer, for the simple reason that abundant evidence now shows that sex influences on brain function are universal, found at every level of neuroscience from the behaving human to the ion channel. These sex influences can modify, negate, or even reverse findings.
Perspectives on Pain
Cahill gives an example from animal research that further emphasizes this point. He cites Mogil and Chanda, who are at the forefront of understanding sex influences on brain mechanisms of pain. Despite the general reluctance to study sex influences on pain, the accumulated evidence clearly demonstrates that neural pain mechanisms are both similar and different in males and females, with the “different” part significantly underrepresented.
This data already allows for the conclusions that studying only males will both lead, and mislead, the search for effective pain treatments in women. After surveying the field, Mogil and Chanda concluded that “given these facts, one might argue that basic scientists are shirking their responsibility to half of the human population by avoiding direct animal models of them. We simply do not see any valid excuses remaining for the continued abundant evidence now shows that sex influences on brain function are universal, found at every level of neuroscience exclusion of female rodents from basic science studies in pain.”
Exciting Times in Neuroscience
“These are exciting times in neuroscience,” says Cahill. “We are uncovering anatomical, chemical and functional differences between the brains of men and women. ”
Researchers are working to determine how these sex-based variations relate to differences in male and female cognition and behavior. Their discoveries could point the way to sex-specific therapies for men and women with neurological conditions such as addiction, depression, schizophrenia and post-traumatic stress disorder (PTSD).”
A PET (Positron Emission Tomography) study by Mirko Diksic and his colleagues at McGill University showed that serotonin production was a remarkable 52 percent higher on average in men than in women, which might help clarify why women are more prone to depression – a disorder commonly treated with drugs that boost the concentration of serotonin.
A similar situation might prevail in addiction. In this case, the neurotransmitter in question is dopamine, a chemical involved in the feelings of pleasure associated with drugs of abuse. While studying female rats, Jill B. Becker and her fellow investigators at the University of Michigan discovered that in females, estrogen boosted the release of dopamine in brain regions important for regulating drug-seeking behavior. Furthermore, the hormone had long-lasting effects, making the female rats more likely to pursue cocaine weeks after last receiving the drug. Such differences in susceptibility – particularly to stimulants such as cocaine and amphetamine – could explain why women might be more vulnerable to the effects of these drugs and why they tend to progress more rapidly from initial use to dependence than men do.
Neuroscientists are still far from identifying all the sex-related variations in the brain. “It’s like a baby taking its first steps,” Cahill explains. The positive news is that there are growing numbers who do agree that
going back to assuming we can evaluate one sex and learn equally about both is no longer an option.
“So the assumption we’re making that sex really doesn’t matter, is not a valid assumption,” says Cahill. “It may not matter. It may matter hugely. It may flip your result – wow, the status quo is not okay. The way we’re doing business has to change.”
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