In this week’s issue of Journal of Neuroscience, there is a unique section entitled “Toolbox” of which I have never seen before. It is mostly a troubleshooting guide for understanding sex differences at physiological and behavioral levels. One of the issues discussed in the review is how to differentiate betweenphenotypic vs genotypic differences in physiological and behavioral processes. Hence, how does one determine if sex hormones or chromosomes underlie sex differences?
I should also mention that I should be careful with my terminology because sex difference, sex dimorphism, and sex divergence each refer to different measures of study; Sex differences refer to differences between males and females along a continuum meaning that the behavior or physiological phenomenon is present in both, but the average is significantly different. Examples include paradigms of learning, memory, and anxiety. Sex dimorphism represents an “all-or-none” phenomenon, such as the fact that male zebra finches produce “love” songs while females do not. Lastly, sexual divergence is used to describe some event that is present at equivocal levels in both males and females, but the underlying neurbiology and circuitry varies greatly, although sex disparities can be induced through environmental and/or physiological challenges. The circuits of parenting behavior is an example of sexual divergence.
In this post, though, I would like to emphasize a really interesting transgenic mouse strain that has been developed to elucidate gonadal vs. genetic sex differences in brain anatomy and very recently, alcohol intake behaviors of which I blogged about two years ago. This mouse line is referred to as the four core genotypes. The unique characteristic of this line is that the gonadal sex can differ from the chromosomal sex due to a spontaneous deletion of the Sry gene, which is the testes-determining gene. Hence, XX+SRY females have testes and XY-SRY males have ovaries. Obviously, XX-SRY females have ovaries and XY+SRY males have testes. Pretty cool and a powerful model of study, right?
McCarthy, M., Arnold, A., Ball, G., Blaustein, J., & De Vries, G. (2012). Sex Differences in the Brain: The Not So Inconvenient Truth Journal of Neuroscience, 32 (7), 2241-2247 DOI: 10.1523/JNEUROSCI.5372-11.2012