Long-term gonadectomy affects the density of tyrosine hydroxylase- but not dopamine-β-hydroxylase-, choline acetyltransferase- or serotonin-immunoreactive axons in the medial prefrontal cortices of adult male rats

Abstract

The rat prefrontal cortices participate in cognitive, affective and mnemonic functions. The importance of dopamine innervation for these computations is illustrated in studies showing that both supranormal levels and chemical lesions of prefrontal dopamine induce severe behavioral deficits. Observed hormone effects on some of these same behaviors suggest that the prefrontal cortices are also sensitive to gonadal steroids. These two influences seem to converge in recent evidence of increased dopamine axon density in representative prefrontal but not sensory or motor cortices in gonadectomized adult male rats. The seeming selectivity of these effects was further explored here using immunocytochemistry for tyrosine hydroxylase, dopamine-β-hydroxylase, serotonin and choline acetyltransferase to label neurochemically identified afferents in remaining, unstudied prefrontal fields of rat cortex in animals that were sham-operated or gonadectomized and given placebo, testosterone propionate, estradiol or dihydrotestosterone 28 days before being killed. Group comparisons revealed that across prefrontal zones, gonadectomy produced androgen-sensitive increases in presumed dopamine axon density, but did not affect the other afferents. These findings thus bolster evidence for a targeted gonadal steroid influence involving the prefrontal cortices and a neurotransmitter essential for their normal operations and implicated in their dysfunction in disorders such as schizophrenia as well.