AROMATASE-IMMUNOREACTIVE CELLS IN THE QUAIL BRAIN - EFFECTS OF TESTOSTERONE AND SEX DIMORPHISM

We previously demonstrated that testosterone (T) increases aromatase a ctivity (AA) and that AA is sexually dimorphic (males > females) in th e quail preoptic area (POA). The precise anatomical localization of th ese effects is, however, impossible to obtain by biochemical assays ev en when samples are dissected by the Palkovits punch technique. We wer e recently able to set up an immunocytochemical (ICC) procedure that p ermits visualization of aromatase-immunoreactive (ARO-ir) cells in the quail brain. This showed that the ARO-ir cells of the quail POA actua lly outline the sexually dimorphic medial preoptic nucleus (POM). This ICC technique was used here to analyze the sex dimorphism of the quai l 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 secti on every 100 mu m throughout the rostral to caudal extent of the POM o f castrated birds that had been treated with increasing doses of T (5, 10, or 20 mm long Silastic implants). These T-treatments produced a d ose-related increase in the sexual behavior of the birds and they incr eased 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 part icularly large amplitude in the part of the POM located under the ante rior commissure (AC). In Experiment 2, the same procedure was used to reanalyze the sex difference of the preoptic aromatase system. This sh owed 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 s eptum 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 gonadectomize d and treated with a same dose of T (40 mm implants). No sex differenc e 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 aromat ase 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. These experiments also indicate th at ARO-ir cells in the region of POM located just under and rostral to AC are sexually dimorphic and T-sensitive, which suggests their invol vement in the control of male sexual behavior. This conclusion is also supported but our recent studies based on electrolytic lesion and ste reotaxic implantation of T in POM.