DISTRIBUTION AND STEROID DEPENDENCE OF AROMATASE ENZYME IMMUNOREACTIVITY IN LIMBIC NUCLEI OF THE FEMALE MUSK SHREW BRAIN

In the female musk shrew (Suncus murinus) neural aromatization of test osterone to estradiol is critical for the expression of sexual behavio r. To localize the brain regions capable of aromatization, we used imm unocytochemistry to map the distribution of aromatase enzyme. Aromatas e immunoreactivity (AROM-ir) has a discrete distribution primarily lim ited to the lateral septum (LS), central nuclei of the amygdala (Ce) a nd the bed nucleus of the stria terminalis (BST). In these nuclei the intensity of immunoreactivity varies with hormonal status. Ovariectomy (OVX) significantly reduces the optical density of AROM-ir neurons in all nuclei as compared with brains of normal females. Combined OVX an d adrenalectomy (ADX) further reduces optical density readings in AROM -ir cells in the LS and BST, as compared with readings from the brains of OVX animals. Normal and ovariectomized females implanted with test osterone had qualitatively equivalent AROM-ir. High levels of aromatas e activity have been measured in the preoptic area and hypothalamus in a number of mammals, including the musk shrew. However, in this exper iment AROM-ir was absent in these areas. We present several hypotheses to account for this discrepancy between previously reported biochemic al data and these histological data. In summary, these data suggest th at limbic nuclei may play a role in the expression of sexual behavior in female musk shrews.