Postepy nauk rolniczych - Instytucja Naukowa - Polska Akademia ...

104 M. Ciechanowska i in.Expression of the GnRH and GnRH receptor(GnRHR) genes in hypothalamus-pituitary systemof ewes during different physiological statesKey words: ewe, hypothalamus, pituitary, GnRH, mRNA GNRH, mRNAGnRHR, receptors: GABA A -ergic, -opioidergic, CRH-ergic,dopaminergic DA-2SummaryThis review is focused on the relationship between the neuroendocrine control ofGnRH/LH secretion and the expression of GnRH and GnRHR genes in the hypothalamic-pituitarysystem during different physiological states of animals and under thestress conditions. In this aspect we analyzed the role of several neurotransmitter/neurohormonesystems in the hypothalamus, i.e. the controlling of GnRH releaseand the expression of GnRH and GnRHR genes.The results obtained on sheep and rats showed that the expression of both genes insome physiological states is to a high degree related to LH secretion but not in others.The neural systems in the hypothalamus, which are involved in the suppression ofGnRH/LH secretion (-endorphinergic, GABA-ergic, CRH-ergic) in the cyclingewes, also inhibit GnRH mRNA expression in the hypothalamus. The infusion of-endorphin, muscimol (GABA A receptor agonist) and CRH decreases GnRH geneexpression. However, agonists and antagonists of -opioidergic, GABA A -ergic andCRH-ergic receptors affect in a specific way the expression of GnRHR gene in discreteareas of the hypothalamus of follicular phase ewes. Thus suggests, that theGnRHR genes of selected hypothalamic structures are located in different neural systems.In the anestrous ewes the increase of LH secretion was followed with the decreasein GnRH mRNA in the ventromedial hypothalamus and GnRHR mRNA in theventromedial hypothalamus/stalk-median eminence after the blockade of dopaminergicDA-2 receptors in the hypothalamus. It is likely that these events are related to anincrease in biosynthesis GnRH with concomitant decreased of GnRHR protein in thehypothalamus allowing to an increase in GnRH release. The increase of GnRH mRNAin the ventromedial hypothalamus after a prolonged infusion of small GnRH dosesinto the third cerebral ventricle suggests that the ultrashort loop of the negative feedbackaction of GnRH in the hypothalamus on the GnRH release is exerted at thegenomic level.Much more information is necessary to establish the precise manner in which severalneurotransmitter/neurohormone systems in the hypothalamus regulate GnRH andGnRHR genes expression and the role of GnRHR mRNAin GnRH gene expression.