Regulation by Androgen of Levels of the β Subunit of Nerve Growth Factor and Its mRNA in Selected Regions of the Mouse Brain

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Abstract
Our previous studies showed that the concentration of the β subunit of nerve growth factor (β‐NGF) in nervous tissues is higher in male than in female mice. To identify the brain regions that are affected by androgens, the amounts of β‐NGF protein and its mRNAs were measured in male, female, and castrated male CD‐1 mice and testicular feminization mice at 3–4 months of age. Among tissues examined, the hypophysis of males contained the highest average concentration of β‐NGF protein. In most regions of the brain, individual levels were more variable in males than in females. However, after the castration, such variations in β‐NGF levels disappeared. Average levels of β‐NGF protein in males were higher in the cerebellum (eightfold higher), olfactory bulb (12‐fold higher), hypothalamus (sixfold higher), and hypophysis (72‐fold higher) than thope in corresponding regions of females. No significant differences were observed in levels of β‐NGF protein in the hippocampus, cerebral cortex, striatum, septum, and brainstem. The castration of male mice caused a reduction in levels of β‐NGF protein in the hypothalamus and hypophysis, but not in the cerebellum and olfactory bulb, to the femgle levels. The concentrations of β‐NGF protein in testicular feminization mice were similar to those in female CD‐1 mice in all regions. The concentrations of mRNA for β‐NGF in the olfactory bulb and hypophysis from males were higher than those from females. By contrast, northern blots showed no remarkable differences in the amounts of brain‐derived neurotrophic factor and neurotrophin‐3 between the two sexes. Thus, in some regions of the brain, the production of β‐NGF appears to be regulated by testosterone, but the regulatory mechanisms do not appear to be simple. Our present results indicate that the binding of testosterone to its receptor is an important step in the regulation of the level of β‐NGF in these region.