A brain sexual dimorphism controlled by adult circulating androgens.
Level 5 - mechanism / opinion, no new human data
Preclinical animal research (CEBM Level 5).
PubMed 10377450 · doi:10.1073/pnas.96.13.7538
What was done
Researchers investigated whether adult circulating hormone levels account for sex differences in regional brain volume. In adult rats, they measured the volume and neuronal soma size (via Nissl staining) of the posterodorsal nucleus of the medial amygdala (MePD) following four weeks of adult male castration or adult female androgen treatment compared to intact controls.
What was found
The abstract does not provide exact numerical values, percentages, or sample sizes. It reports that intact male rats have a significantly larger MePD volume than intact females. Castration of adult males reduced MePD volume to female baseline levels within four weeks. Conversely, treating adult females with androgens for four weeks enlarged MePD volume to levels equivalent to intact males. Parallel changes were observed in MePD neuronal soma size.
Why it matters
This study demonstrates that some structural brain sexual dimorphisms in mammals are not permanent developmental fixtures established strictly perinatally, but can be fully driven and reversed by circulating androgens in adulthood. This highlights circulating adult hormones as a crucial potential confounder in human neuroimaging and post-mortem studies comparing demographic or clinical groups.
Limits
The study was conducted entirely in a rodent model, so findings cannot be directly extrapolated to human brain sexual dimorphisms without clinical verification. The abstract omits sample sizes, specific androgen dosages, statistical metrics, confidence intervals, and whether other brain regions or functional behavioral outcomes were evaluated alongside structural changes.
Cited by
- supports Research by Brad Cooke demonstrated that the sex difference in the medial amygdala in animals disappears within a few weeks following testosterone removal in adult males.