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The short-term effects of administering testosterone propionate (TP) to 4-day female rats (androgenized females) on the synthesis of specific brain proteins were investigated. At various times after the intraperitoneal injection of TP or arachis oil, [35S]methionine was injected into the third ventricle and 1 h later proteins were extracted from the hypothalamus-preoptic area (H-POA) and analyzed by sodium dodecyl sulphate polyacrylamide gel electrophoresis. Changes in synthesis of two 13,000-14,000 mol. wt. proteins in the 4-day rat brain were detected, and these changes appeared to be specific for the H-POA. In addition, silver staining revealed a 50,000 mol. wt. protein which was present in the male and androgenized female H-POA but not in the oil-treated female H-POA. An incidental, but potentially important finding, was the synthesis of a 77,600 mol. wt. protein in the H-POA of one animal which had several seizures during the experiment. These results show that changes in the synthesis of specific proteins occur in the H-POA of neonatal female rats within 8 h of TP administration and support the hypothesis that hormone-induced changes in brain protein synthesis may be involved in sexual differentiation of the brain.

We have investigated the changes in the concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the hypothalamus-preoptic area (HPOA) and midbrain raphe (MR) region of male and female rats throughout development. No sex differences were found in the concentrations of the indoleamines in either of the areas investigated at any stage of development. The 5-HIAA/5-HT molar ratio was maximal at 4 days of age in both the HPOA and MR. A small but significant sex difference in the 5-HIAA/5-HT ratio occurred in the HPOA (higher in males) but not in the MR at 40 days of age, and the ratio was significantly greater in 80-day-old female rats in the HPOA but not MR. Studies using NSD 1015 to block the conversion of 5-hydroxytryptophan to 5-HT showed that a higher rate of 5-HT synthesis occurred in the HPOA of 80-day-old rats compared with the neonatal HPOA and that in 80-day-old rats the rate of 5-HT synthesis was significantly higher in females. These results show that endogenous steroids do not affect the activity of serotoninergic neurons in the HPOA or MR either during or immediately after the critical period of sexual differentiation. In addition, the results from the NSD 1015 experiments show that the high 5-HIAA/5-HT ratio found in neonates does not involve a higher rate of 5-HT synthesis than that in adult rats.

To investigate possible sex differences in central catecholaminergic systems, the concentrations of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured by high-performance liquid chromatography with electrochemical detection in the hypothalamus-preoptic area (H-POA) and midbrain raphe (MR) region of male and female rats throughout postnatal development. Other than a small but significant sex difference in DA concentration in the MR at 36 h (higher in females), the results showed that there were no sex differences in the concentrations of DA or DOPAC at any age in either brain region. The developmental profiles of the concentrations of DA and DOPAC showed that DAergic systems in the H-POA are immature at birth, with concentrations increasing steadily until 80 days of age, but in the MR concentrations reach a maximum at 20 days of age; a situation which is perhaps a reflection of differing monoamine metabolism in the two areas.