Aromatase-immunoreactive cells in the quail brain: effects of testosterone and sex dimorphism.

We previously demonstrated that testosterone (T) increases aromatase activity (AA) and that AA is sexually dimorphic (males > females) in the quail preoptic area (POA). The precise anatomical localization of these effects is, however, impossible to obtain by biochemical assays even when samples are dissected by the Palkovits punch technique. We were recently able to set up an immunocytochemical (ICC) procedure that permits visualization of aromatase-immunoreactive (ARO-ir) cells in the quail brain. This showed that the ARO-ir cells of the quail POA actually outline the sexually dimorphic medial preoptic nucleus (POM). This ICC technique was used here to analyze the sex dimorphism of the quail preoptic aromatase and the localization of T effects on ARO-ir cells. In Experiment 1, the number of ARO-ir cells was counted in one section every 100 microns throughout the rostral to caudal extent of the POM of castrated birds that had been treated with increasing doses of T (5, 10, or 20 mm long Silastic implants). These T-treatments produced a dose-related increase in the sexual behavior of the birds and they increased the number of ARO-ir cells in POM, in the septal regions, and in the bed nucleus of the stria terminalis (BNST). The effect had a particularly large amplitude in the part of the POM located under the anterior commissure (AC). In Experiment 2, the same procedure was used to reanalyze the sex difference of the preoptic aromatase system. This showed that the POM of adult males contains more stained cells than the POM of females but only in a restricted region located just under and rostral to the AC. No significant sex difference was observed in the septum or in the BNST. In Experiment 3, the number of ARO-ir cells was determined in the POM of males and females that had been gonadectomized and treated with a same dose of T (40 mm implants). No sex difference in the number of ARO-ir cells could be detected in these conditions. This suggests that the sex difference in AA that had been previously observed in T-treated birds results either from a difference in aromatase concentration or activity in a similar number of positive cells or from a difference in the number of ARO-ir cells that is very discrete from the anatomical point of view.(ABSTRACT TRUNCATED AT 400 WORDS)