Regionally selective effects of gonadectomy on cortical catecholamine innervation in adult male rats are most disruptive to afferents in prefrontal cortex.

Changes in gonadal hormones induced early in life produce substantial, seemingly permanent decreases in tyrosine hydroxylase (TH)-immunoreactive axon density in sensory, motor and prefrontal regions in the rat cerebral cortex. Less is known, however, about the responsiveness of cortical catecholamines to hormone stimulation during adulthood. In this study we expanded upon an earlier analysis of the effects of acute (4 day) and chronic (28 day) gonadectomy in adult male rats on TH innervation in right hemifield of the cingulate cortex to include assessment of sensorimotor areas previously examined following perinatal gonadectomy, the left cingulate hemifield, and one additional prefrontal area - the dorsal anterior insular cortex. Qualitative and quantitative analyses of immunoreactivity revealed modest, transient declines in innervation in sensorimotor areas 4 days after gonadectomy, and a return to normal innervation densities by 28 days after surgery. In cingulate and insular cortices, however, strikingly depleted axon densities observed following acute gonadectomy rebounded to significantly higher than normal levels of innervation 3 weeks later. All effects were attenuated in gonadectomized animals supplemented with testosterone. Thus, for cortical catecholamine innervation, as for other endpoints of hormone stimulation, gonadal steroid sensitivity appears to change dramatically with lifestage. In adult male rats, this sensitivity is also marked by a seemingly selective vulnerability of catecholamine innervation in prefrontal areas to changes in the hormone environment induced by gonadectomy.