There is increasing evidence that in the rat prior to and during the preovulatory LH surge, release rates of GABA in the preoptic area (POA) are decreased while no such changes occurred in the mediobasal hypothalamus (MBH). In addition, GnRH release appears to be facilitated by an increased preoptic excitation of glutamate (GLU). To investigate whether such changes of secretory activity of intrahypothalamic GABA or GLU neurons are associated with altered gene expression of biosynthetic enzymes or transporter proteins characteristic for either neuronal system, we determined mRNA levels of the two forms of the GABA-synthesizing enzyme glutamate decarboxylase (GAD65 and GAD67), the glutamate-synthesizing enzyme glutaminase (GLS), the GABA transporter type 1 (GAT-1) and the glutamate-aspartate transporter type 1 (GLAST). Competitive RT-PCRs using mutant cRNAs as internal standards were conducted with mRNA extracted from microdissected tissue of POA and MBH from diestrous, proestrous, and estrous rats. Proestrous animals were subgrouped according to their endocrine status as follows: ‘prior to’, on the ‘ascending’ or on the ‘descending’ limb of the LH peak, and ‘after the LH surge (post)’. During the preovulatory LH surge, mRNA concentrations of GAD67 and GAT-1 in the POA were significantly increased compared to those observed on diestrous (2.8-fold for GAD67 and 2.5-fold for GAT-1, p < 0.01), while in the MBH the amount of both mRNAs remained constant. The expression levels of GAD65, GLS and GLAST were without any changes in the POA as well as in the MBH. These findings support the hypothesis that in rats induction of the preovulatory LH surge is controlled at the level of GnRH perikarya, and suggest that altered activities of intrapreoptic GABA neurons at both transcriptional and secretory levels are pivotal for the preovulatory activation of GnRH neurons.

Tappaz ML, Wassef M, Oertel WH, Paut L, Pujol JF: Light- and electron-microscopic immunocytochemistry of glutamic acid decarbocylase in the basal hypothalamus: Morphological evidence for neuroendocrine gamma-aminobutyrate. Neuroscience 1983;9:271&ndash;287.
Decavel C, Van den Pol AN: Converging GABA- and glutamate-immunoreactive axons make synaptic contact with identified hypothalamic neurosecretory neurons. J Comp Neurol 1992;316:104&ndash;116.
Goldsmith PC, Thind KK, Perera AD, Plant TM: Glutamate-immunoreactive neurons and their gonadotropin-releasing hormone-neuronal interactions in the monkey hypothalamis. Endocrinology 1994;134:858&ndash;868.
Leranth CS, MacLusky NJ, Sakamoto HS, Shanabrough M, Naftolin F: Glutamic acid decarboxylase-containing axons synapse on LHRH neurons in the rat medial preoptic area. Neuroendocrinology 1985;40:536&ndash;539.
Thind KK, Goldsmith PC: Glutamate and GABAergic neurointeractions in the monkey hypothalamus: A quantitative immunomorphological study. Neuroendocrinology 1995;61:471&ndash;485.
Jarry H, Perschl A, Wuttke W: Further evidence that preoptic anterior hypothalamic GABAergic neurons are part of the GnRH pulse and surge generator. Acta Endocrinol (Copenh) 1988;118:573&ndash;579.
Donoso AO, Banzan AM: Blockade of the LH surge and ovulation by GABA-T inhibitory drugs that increase brain GABA levels in rats. Psychoneuroendocrinology 1986;11:429&ndash;435.
Herbison AE, Dyer RG: Effect on luteinizing hormone secretion of GABA receptor modulation in the medial preopetic area at the time of proestrous luteinizing hormone surge. Neuroendocrinology 1991;53:317&ndash;320.
Fl&uuml;gge G, Oertel WH, Wuttke W: Evidence for estrogen-receptive GABAergic neurons in the preoptic/anterior hypothalamic area of the rat brain. Neuroendocrinology 1986;43:1&ndash;5.
Poletti A, Melcangi RC, Negri-Cesi P, Maggi R, Martini L: Steroid binding and metabolism in the luteinizing hormone-releasing hormone-producing neuronal cell line GT1-1. Endocrinology 1994;135:2623&ndash;2628.
Shen ES, Meade EH Jr, Perez MC, Deecher DC, Negro-Vilar A, L&oacute;pez FJ: Expression of functional estrogen receptors and galanin messenger ribonucleic acid in immortalized luteinizing hormone-releasing hormone neurons: Estrogenic control of galanin gene expression. Endocrinology 1998;139:939&ndash;948.
Butler JA, Sjoberg M, Coen CW: Evidence for oestrogen receptor alpha-immunoreactivity in gonadotrophin-releasing hormone-expressing neurones (see comments). J Neuroendocrinol 1999;11:331&ndash;335.
Brann DW: Glutamate: A major excitatory transmitter in neuroendocrine regulation. Neuroendocrinology 1995;61:213&ndash;225.
Brann DW, Mahesh VB: Endogenous excitatory amino acid involvement in the preovulatory and steroid-induced surge of gonadotropins in the female rat. Endocrinology 1991;128:1541&ndash;1547.
Luderer U, Strobl FJ, Levine JE, Schwartz NB: Differential gonadotropin responses to N-methyl-D,L-aspartate in metestrous, proestrous, and ovariectomized rats. Biol Reprod 1993;48:857&ndash;866.
Lee WS, Abbud R, Hoffman GE, Smith MS: Effects of N-methyl-D-aspartate receptor activation of cFos expression in luteinizing hormone-releasing hormone neurons in female rats. Endocrinology 1993;133:2248&ndash;2254.
Ondo JG, Pass KA, Baldwin R: The effects of neurally active amino acids on pituitary gonadotropin secretion. Neuroendocrinology 1976;21:79&ndash;84.
Arias P, Jarry J, Leonhardt S, Moguilevsky JA, Wuttke W: Estradiol modulates the LH release response to N-methyl-D-aspartate in adult female rats: Studies on hypothalamic luteinizing hormone-releasing hormone and neurotransmitter release. Neuroendocrinology 1993;57:710&ndash;715.
Bourguignon JP, G&eacute;rard A, Franchimont P: Direct activation of gonadotropin-releasing hormone secretion through different receptors to neuroexcitatory amino acids. Neuroendocrinology 1989;49:402&ndash;408.
Thind KK, Goldsmith PC: Expression of estrogen and progesterone receptors in glutamate and GABA neurons of the pubertal female monkey hypothalamus. Neuroendocrinology 1997;65:314&ndash;324.
Jarry H, Leonhardt S, Schwarze T, Wuttke W: Preoptic rather than mediobasal hypothalamic amino acid neurotransmitter release regulates GnRH secretion during the estrogen-induced LH surge in the ovariectomized rat. Neuroendocrinology 1995;62:479&ndash;486.
Erlander MG, Tillakaratne NJ, Feldblum S, Patel N, Tobin AJ: Two genes encode distinct glutamate decarboxylases. Neuron 1991;7:91-100.
Kaufman DL, Houser CR, Tobin AJ: Two forms of the gamma-aminobutyric acid synthetic enzyme glutamate decarboxylase have distinct intraneuronal distributions and cofactor interactions. J Neurochem 1991;56:720&ndash;723.
Kaneko T, Mizuno K: Glutamate-synthesizing enzymes in GABAergic neurons of the neocortex: A double immunofluorescence study in the rat. Neuroscience 1994;61:839&ndash;849.
Herbison AE, Augood S, McGowan EM: Expression of glutamic acid decarboxylase messenger RNA in rat medial preopetic area neurones during the oestrous cycle and after ovariectomy. Brain Res Mol Brain Res 1992;14:310&ndash;316.
Grattan DR, Rocca MS, Strauss KI, Sagrillo CA, Selmanoff MK, McCarthy MM: GABAergic neuronal activity and mRNA levels for both forms of glutamic acid decarboxylase (GAD65 and GAD67) are reduced in the diagonal band of Broca during the afternoon of proestrus. Brain Res 1996;733:46&ndash;55.
Hebison AE, Augoods SJ, Simonian SX, Chapman C: Regulation of GABA transporter activity and mRNA expression by estrogen in rat preoptic area. J Neurosci 1995;15:8302&ndash;8309.
Leonhardt S, Jarry H, Kreipe A, Werstler K, Wuttke W: Pituitary adenylate cyclase activating polypeptide stimulates pituitary hormone release in male rats. Neuroendocrinol Lett 1992;14:319&ndash;328.
Palkovits M: Isolated removal of hypothalamic or other brain nuclei of the rat. Brain Res 1973;59:449&ndash;450.
Pellegrino LJ, Pellegrino AS, Cushman AJ: A Stereotaxic Atlas of the Rat Brain, ed 2. New York, Plenum Publishing, 1979.
Guastella J, Nelson N, Nelson H, Czyzyk L, Keynan S, Miedel MC, Davidson N, Lester HA, Kanner BI: Cloning and expression of a rat brain GABA transporter. Science 1990;249:1303&ndash;1306.
Wyborski RJ, Bond RW, Gottlieb DI: Characterization of a cDNA coding for rat glutamic acid decarboxylase. Brain Res Mol Brain Res 1990;8:193&ndash;198.
Banner C, Hwang JJ, Shapiro RA, Wenthold RJ, Nakatani Y, Lampel KA, Thomas JW, Huie D, Curthoys NP: Isolation of a cDNA for rat brain glutaminase. Brain Res 1988;427:247&ndash;254.
Storck T, Schulte S, Hofmann K, Stoffel W: Structure, expression, and functional analysis of a Na(&plus;)-dependent glutamate/aspartate transporter from rat brain. Proc Natl Acad Sci USA 1992;89:10955&ndash;10959.
Kephart D: Quantitative RT-PCR: Rapid construction of templates for competitive amplification. Promega Notes 1998;68:16&ndash;19.
Jarry H, Hirsch B, Leonhardt S, Wuttke W: Amino acid neurotransmitter release in the preopetic area of rats during the positive feedback actions of estradiol on LH release. Neuroendocrinology 1992;56:133&ndash;140.
Ping L, Mahesh VB, Wiedmeier VT, Brann DW: Release of glutamate and aspartate from the preoptic area during the progesterone-induced LH surge: In vivo microdialysis studies. Neuroendocrinology 1994;59:318&ndash;324.
Unda R, Brann DW, Mahesh VB: Progesterone suppression of glutamic acid decarboxylase (GAD67) mRNA levels in the preoptic area: Correlation to the luteinizing hormone surge. Neuroendocrinology 1995;62:562&ndash;570.
Szwarcfarb B, Carbone S, Stein ML, Medina, J, Moguilevsky JA: Sexual differences in the effect of the GABAergic system on LH secretion and in the hypothalamic ontogenesis of GABAA receptors in prepubertal rats. Brain Res 1994;646:351&ndash;355.
Bourguignon JP, G&eacute;rard A, Alvarez-Gonzalez ML, Franchimont P: Role of excitatory amino acids in the physiological neuroendocrine mechanisms of puberty. Front Endocrinol 1995;10:215&ndash;223.
Merchenthaler I, S&eacute;t&aacute;l&oacute; G, Petrusz P, Negro-Vilar A, Fl&eacute;rk&oacute; B: Identification of hypophysiotropic luteinizing hormone-releasing hormone neurons by combined retrograde labeling and immunocytochemistry. Exp Clin Endocrinol 1989;94:133&ndash;140.
Okamura H, Abitbol M, Julien JF, Dumas S, Berod A, Geffard M, Kitahama K, Bobillier P, Mallet J, Wiklund L: Neurons containing messenger RNA encoding glutamate decarboxylase in rat hypothalamus demonstrated by in situ hybridization, with special emphasis on cell groups in medial preoptic area, anterior hypothalamic area and dorsomedial hypothalamic nucleus. Neuroscience 1990;39:675&ndash;699.
Jennes L, Stumpf WE, Tappaz ML: Anatomical relationships of dopaminergic and GABAergic systems with the GnRH systems in the septo-hypothalamic area. Immunohistochemical studies. Exp Brain Res 1983;50:91&ndash;99.
Borden LA, Smith KE, Vaysse PJ, Gustafson EL, Weinshank RL, Branchek TA: Re-evaluation of GABA transport in neuronal and glial cell cultures: Correlation of pharmacology and mRNA localization. Receptors Channels 1995;3:129&ndash;146.
Durkin MM, Smith KE, Borden LA, Weinshank RL, Branchek TA, Gustafson EL: Localization of messenger RNAs encoding three GABA transporters in rat brain: An in situ hybridization study. Brain Res Mol Brain Res 1995;33:7&ndash;21.
Swan M, Najlerahim A, Watson RE Jr, Bennett JP: Distribution of mRNA for the GABA transporter GAT-1 in the rat brain: Evidence that GABA uptake is not limited to presynaptic neurons. J Anat 1994;185:315&ndash;323.
Rattray M, Priestley JV: Differential expression of GABA transporter-1 messenger RNA in subpopulations of GABA neurones. Neurosci Lett 1993;156:163&ndash;166.
Borden LA: GABA transporter heterogeneity: Pharmacology and cellular localization. Neurochem Int 1996;29:335&ndash;356.
Leonhardt S, Shahab M, Luft H, Wuttke W, Jarry H: Reduction of LH secretion induced by long-term feed restriction in male rats is associated with increased expression of GABA-synthesizing enzymes without alterations of GnRH gene expression. J Neuroendocrinol 1999;11:613&ndash;619.
Roth C, Leonhardt S, Theiling K, Lakomek M, Jarry H, Wuttke W: Ontogeny of the GnRH-, glutaminase- and glutamate decarboxylase-gene expression in the hypothalamus of female rats. Brain Res Dev Brain Res 1998;110:105&ndash;114.
Rothstein JD, Martin L, Levey AI, Dykes-Hoberg M, Jin L, Wu D, Nash N, Kuncl RW: Localization of neuronal and glial glutamate transporters. Neuron 1994;13:713&ndash;725.
Schmitt A, Asan E, Puschel B, Kugler P: Cellular and regional distribution of the glutamate transporter GLAST in the CNS of rats: Nonradioactive in situ hybridization and comparative immunocytochemistry. J Neurosci 1997;17:1-10.
Gegelashvili G, Civenni G, Racagni G, Danbolt NC, Schousboe I, Schousboe A: Glutamate receptor agonists up-regulate glutamate transporter GLAST in astrocytes. Neuroreport 1996;8:261&ndash;265.
Kimura F, Nishihara M, Hiruma H, Funabashi T: Naloxone increases the frequeny of the electrical activity of luteinizing hormone-releasing hormone pulse generator in long-term ovariectomized rats. Neuroendocrinology 1991;53:97&ndash;102.
Hiruma H, Sano A, Kimura F: Injection of bicuculline elicits firing of luteinizing hormone-releasing hormone pulse generator in muscimol-treated ovariectomized rats. Brain Res 1994;641:191&ndash;197.
Bourguignon JP, G&eacute;rard A, Debougnoux G, Rose J, Franchimont P: Pulsatile release of gonadotropin-releasing hormone (GnRH) from the rat hypothalamus in vitro: Calcium and glucose dependency and inhibition by superactive GnRH analogs. Endocrinolgoy 1987;121:993&ndash;999.
Purnelle G, G&eacute;rard A, Czajkowski V, Bourguignon JP: Pulsatile secretion of gonadotropin-releasing hormone by rat hypothalamic explants of GnRH neurons without cell bodies. Neuroendocrinology 1997;66:305&ndash;312.
Terasawa E, Luchansky LL, Kasuya E, Nyberg CL: An increase in glutamate release follows a decrease in gamma-aminobutyric acid and the pubertal increase in luteinizing hormone-releasing hormone release in the female rhesus monkeys. J Neuroendocrinol 1999;11:275&ndash;282.
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