EXPRESSION OF ESTROGEN-RECEPTOR IN THE FACIAL NUCLEUS IS SUPPRESSED BY ESTRADIOL, BUT NOT BY TESTOSTERONE, INDICATING A LACK OF REQUIREMENTFOR AROMATIZATION

The transient expression of estrogen receptor (ER) in the ventromedial subnucleus of the facial nucleus was previously detected in the newbo rn rat, and the expression of ER molecules was down-regulated by daily injections of estradiol. Here we examined possible involvement of aro matization in this process. ER molecules were measured by immunohistoc hemistry and in situ hybridization histochemistry after daily injectio ns of testosterone propionate (TP;100 mu g/0.02 ml) and estradiol benz oate (EB; 10 mu g/0.02 ml) in the male pups castrated within 24 h of b irth. Daily injections of TP for 5 consecutive days did not suppress E R and ER mRNA in the facial nucleus, while they were both suppressed b y daily injections of EB. Moreover, aromatase immunoreactivity was not detected in the facial nucleus of both castrated, TP injected and int act control males at 6 days of age. The present findings therefore sug gest that ER molecules expressed transiently in the facial nucleus are not directly involved in masculine sexual differentiation of the brai n in newborn rat.