Distribution of aromatase mRNA in the ram hypothalamus: An In situ hybridization study

The regional distribution of neurones expressing aromatase mRNA in the ram hypothalamus was examined by in situ hybridization using P-33-labelled cRNA probes. The highest amounts of hybridization signal were observed in the c entral part of the medial preoptic nucleus and posterior medial part of the bed nucleus of the stria terminalis. Moderate amounts of hybridization sig nal were observed in the anteroventral periventricular preoptic nucleus, me dial preoptic nucleus and a broad band extending between the medial preopti c nucleus and bed nucleus of the stria terminalis. Low levels of hybridizat ion signal were observed in the organum vasculosum of the lamina terminalis , anterior part of the medial preoptic nucleus, and central part of the ven tromedial nucleus of the hypothalamus. The presence of aromatase mRNA withi n neurones of the steroid-sensitive hypothalamic circuit supports a role fo r aromatization in the mechanism of testosterone action on reproductive fun ction in male sheep. The distribution of aromatase mRNA in the ovine hypoth alamus was similar to that described for other vertebrate species, suggesti ng a high degree of functional conservation across species.