TEMPORAL REGULATION BY ESTROGEN OF BETA-PREPROTACHYKININ MESSENGER-RNA EXPRESSION IN THE RAT VENTROMEDIAL NUCLEUS OF THE HYPOTHALAMUS

In the rat, reproduction and sexual behavior are controlled by the gon adal steroid regulation of synaptic interactions within the sexually d imorphic limbic-hypothalamic system. The effects of estrogen on the ve ntromedial nucleus of the hypothalamus, one nucleus within the circuit , are central to the modulation of this behavior. Involvement of the n europeptide substance P, a member of the tachykinin family of neuropep tides, has been implicated in the regulation of both lordosis behavior and gonadotropin release. However, previous studies have provided con flicting evidence as to whether levels of substance P in the ventromed ial nucleus of the hypothalamus are modulated by circulating estrogens . To study this question further, in situ hybridization histochemistry was used to examine levels of beta-preprotachykinin mRNA, which encod es substance P and other tachykinins, in the ventrolateral subdivision of the ventromedial hypothalamus at 10 consecutive timepoints over a 4 day period subsequent to an acute administration of estrogen. Follow ing estrogen treatment, beta-preprotachykinin mRNA expression was incr eased in cells of the ventrolateral portion of the ventromedial nucleu s of the hypothalamus which constitutively express beta-preprotachykin in mRNA; however, there were no statistically significant changes in t he number of cells that express detectable levels of beta-preprotachyk inin mRNA in the ventrolateral portion of the ventromedial nucleus. Es trogen treatment produced two peaks of beta-preprotachykinin mRNA expr ession, the first at 2 h and the second at 48 h after the injection of estrogen. These data indicate that estrogen has both rapid and prolon ged effects on beta-preprotachykinin mRNA levels, suggesting that estr ogen may affect different cellular mechanisms relavent to the inductio n of beta-preprotachykinin mRNA expression.