Neurochemical control of rapid stress-induced changes in brain aromatase activity

In the male brain, the medial preoptic nucleus (POM) is known to be a critical relay for the activation
of sexual behaviour, with the aromatisation of testosterone into 17b-oestradiol (E2) playing
a key role. Acute stress has been shown to differentially modulate the aromatase enzyme in
this and other brain nuclei in a sex-specific manner. In POM specifically, stress induces increases
in aromatase activity (AA) that are both rapid and reversible. How the physiological processes
initiated during an acute stress response mediate sex- and nuclei- specific changes in AA and
which stress response hormones are involved remains to be determined. By examining the relative
effects of corticosterone (CORT), arginine vasotocin (AVT, the avian homologue to arginine
vasopressin) and corticotrophin-releasing factor (CRF), the present study aimed to define the
hormone profile regulating stress-induced increases in AA in the POM. We found that CORT,
AVT and CRF all appear to play some role in these changes in the male brain. In addition, these
effects occur in a targeted manner, such that modulation of the enzyme by these hormones
only occurs in the POM rather than in all aromatase-expressing nuclei. Similarly, in the female
brain, the experimental effects were restricted to the POM but only CRF was capable of inducing
the stress-like increases in AA. These data further demonstrate the high degree of specificity
(nuclei-, sex- and hormone-specific effects) in this system, highlighting the complexity of the
stress–aromatase link and suggesting modes through which the nongenomic modulation of this
enzyme can result in targeted, rapid changes in local oestrogen concentrations.