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Prozac and the Gay Brain July 7, 2009

Posted by Geekgirl in brain, psychology.
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Could it be that our brains respond differently from one another to anti-depressants? More to the point, do straight men and gay men have different reactions to Prozac? Researchers at the University of Chicago studies activation of the brain in straight men versus gay men. While there were differences within groups, there were clear differences between the two groups.

Please note. This study was not about the effectiveness of treatment with anti-depressants. Treatment with anti-depressants is still a trial and error method. No one really knows why one person reacts well and a different person has a poor reaction to the same drug. However, anti-depressants do act on parts of the brain that also process sexual behavior.

Differential brain activation in exclusively homosexual and heterosexual men produced by the selective serotonin reuptake inhibitor, fluoxetineD

Leann H. Kinnunena,*, Howard Moltzb, John Metzc,e, Malcolm Cooperd

aCommittee on Human Development, University of Chicago, 5848 S. University Avenue, Chicago, IL 60637, United States

bDepartment of Psychology, University of Chicago, Chicago, IL, United States

cDepartment of Psychiatry, University of Chicago, Chicago, IL, United States

dClinical Research Center, University of Chicago, Chicago, IL, United States

eInsight Sciences, Chicago, IL, United States

Accepted 9 July 2004

Available online 12 September 2004

Abstract

A number of studies have shown a relationship between bsexual orientation and size of various brain nuclei. We hypothesized that neurotransmitter differences might parallel neuroanatomical differences in the hypothalamus. We administered 40 mg of fluoxetine as a challenge to the serotonergic systems of exclusively homosexual and exclusively heterosexual men and measured cerebral metabolic changes with fluorodeoxyglucose positron emission tomography (FDG-PET). The metabolic differences we observed might reflect underlying neurochemical differences between homosexual and heterosexual men.

D 2004 Elsevier B.V. All rights reserved

Researchers at the University of Chicago studies the brains of homosexual and heterosexual men after giving them a dose of fluoxetine,  or a placebo. Researchers know that many areas of the brain have been reported to have gender differences, including differences between gay individuals and straight individuals. Some of the regions include the hypothalamus, This portion of the brain is significantly smaller in the brains of homosexual men than in those of heterosexual men.. The anterior hypothalamus contains a section called the mPOA. The mPOA is critical for the expression of sexual behavior in male animals and receives indirect input from virtually every sensory modality.

The researchers  hypothesized that a relationship might also exist between sexual orientation and brain neurotransmitters, especially those exhibiting sex differences and affecting sexual behavior. Dopamine (DA) and serotonin (5-HT) have been implicated in the process of neonatal brain sexual differentiation, and sex differences exist in levels of these neurotransmitters and/or their metabolites. In addition, both affect masculine sexual behavior.

Test subjects were chosen from the two extremes. Heterosexual men who claimed to only have heterosexual experiences and homosexual men who claimed to only have homosexual experiences. This was done to minimize diversity between individuals.

Different effects were observed in the region including the hypothalamus, with the homosexual group exhibiting a significantly( p V0.01) smaller reduction in hypothalamic glucose metabolism in response to fluoxetine than the heterosexual group. Areas not known to play a role in sexual behavior were activated differentially as well.  The fact that the response of the homosexual group appears larger in spatial extent than that of the heterosexual group may be due to greater heterogeneity within the heterosexual group.

This study is the first to report evidence of a sexual orientation-related metabolic difference produced by a pharmacologic challenge, possibly reflecting under lying between-groups differences in neurochemical activity.

Our results also suggest the possibility that homosexual and heterosexual individuals may respond differently to SSRIs, particularly with regard to side effects. In conclusion, it should be mentioned that the failure of previous studies to report differences between homosexual and heterosexual men might be related to within group heterogeneity in those subjects. Specifically, individuals of diverse sexual orientations have been included routinely under the rubric of either homosexual or heterosexual, based solely on their declared sexual preference.

Even though the researchers chose individuals on the extremes, they still saw a lot of variation within the heterosexual men and within the homosexual men.

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