ANATOMIC DISTRIBUTION AND REGULATION OF AROMATASE GENE-EXPRESSION IN THE RAT-BRAIN

Recent evidence suggests that two cytochrome P450 aromatase (P450(arom )) mRNA transcripts are present in the rat brain. One of these contain s the entire 5'-coding sequence and correlates with the presence of fu nctional enzyme. We designed a new 255-base pair P450(arom) probe (ARO M255) that recognizes only this full-length P450(arom) mRNA. Ribonucle ase protection assays verified that the cRNA probe synthesized from th is construct recognized a single RNA species in brain tissues that exp ress aromatase activity, but not in the cingulate cortex, an area prev iously shown to contain only the alternate transcript. Moreover, the P 450(arom) mRNA content of the preoptic area was significantly lower in castrates than in intact males or testosterone (T)-treated castrates. We employed P-33-labeled cRNA probes to examine the distribution of P 450(arom) mRNA by in situ hybridization. High levels of mRNA were dete cted in the medial preoptic nucleus (MPN), bed nucleus of the stria te rminalis (BnST), and medial amygdala (MA). Lower levels were found in the ventromedial hypothalamic nucleus and cortical amygdala. The magni tude of the hybridization signal in the BnST and MPN was greater in ma les than in females. Treatment with T propionate significantly increas ed hybridization signal in BnST, MPN, and MA. These results confirm th e anatomic distribution of P450(arom) mRNA within hypothalamic and lim bic nuclei of the adult male rat and demonstrate that steady state con centrations are regionally regulated by T. Moreover, they demonstrate the necessity of using a molecular probe that can distinguish between P450(arom) variants in the brain.