Neurotransmitter and gonadal steroid regulation of reproductive behavior and estrogen receptor in the female guinea pig

Noradrenergic and gonadal steroid hormone receptor mediated signals interact within the brain to influence reproductive behavior of female guinea pigs. Gonadal steroids autoregulate gonadal steroid receptors within the brain in ways that may also influence reproduction. Studies in this thesis investigate (1) gonadal steroid and noradrenergic interactions influencing lordosis and (2) gonadal steroid regulation of estrogen receptor in brain.; In Chapter I, clonidine (alpha agonist) infused in the medial basal hypothalamus facilitated lordosis in estrogen treated females. Inhibiting alpha neurotransmission (phentolamine) in the medial basal hypothalamus inhibited lordosis in estradiol-17{dollar}beta{dollar} and progesterone treated females. Blockade of alpha-adrenergic receptors in the medial preoptic area transiently increased lordotic responding. These results indicate that alpha receptor mediated signals in the medial basal hypothalamus and the medial preoptic area regulate separate components of the lordosis controlling neuronal network.; In Chapter II altering alpha-1 neurotransmission within the medial preoptic area or the medial basal hypothalamus had little influence on lordosis in estradiol-17{dollar}beta{dollar} and progesterone treated females. Alpha-2 stimulation (UK-14,304) in the medial basal hypothalamus or the medial preoptic area facilitated lordosis. Blocking alpha-2 neurotransmission (yohimbine) in the medial basal hypothalamus inhibited lordosis. Hence, alpha-2-adrenergic stimulation in the medial basal hypothalamus and the medial preoptic area seems to facilitate lordosis.; The effect of decreasing alpha-1 neurotransmission on estrogen receptor protein in the brain was studied in Chapter III. Systemic alpha-1 antagonist (prazosin) treatment did not decrease estrogen receptor immunostaining in any forebrain region investigated. This result suggests that decreases in estrogen binding after inhibition of alpha-1 neurotransmission are not reflected by decreases in estrogen receptor protein.; In Chapter IV, the periventricular preoptic area was found to have the highest and the bed nucleus of the stria terminalis the lowest density of cells containing estrogen receptor mRNA of any forebrain regions analyzed using in situ hybridization. Cells within the bed nucleus of the stria terminalis and the medial preoptic nucleus contained low abundance of estrogen receptor mRNA. Estradiol-17{dollar}beta{dollar}, estradiol-17{dollar}beta{dollar} benzoate or estradiol-17{dollar}beta{dollar} benzoate followed by progesterone did not influence estrogen receptor mRNA. These results demonstrate that ER mRNA content varies across brain regions.