Postnatal development of neurons expressing NADPH-diaphorase and parvalbumin in the parietal cortex of male and female rats

Expression of the enzyme nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and the calcium-binding protein parvalbumin was studied in the parietal cortex of male and female rats during postnatal development at 20, 60 and 90 days of age. First, localization of the activity of NADPH-d was combined with the immunohistochemical localization of parvalbumin to facilitate recognition of morphological details and distribution patterns of these two types of cortical neurons. Double staining of neurons for parvalbumin and NADPH-d was never found. Second, it was found that NADPH-d is a simple and proper marker for quantitative studies. Morphometric analysis revealed sexual dimorphism in the density of NADPH-d-positive neurons in 20 days-old prepubertal rats. Females showed higher amounts of NADPH-d-positive neurons than males. No sex-dependent differences were detected in 60 days-old pubertal and 90 days-old postpubertal rats. The present results suggest that sex differences in the number of NADPH-d-positive neurons in the rat parietal cortex may be related to epigenetic effects of gonadal hormones in the early prepubertal period of postnatal development.