The long-term objectives of these experiments are to explore the biphasic effects of 15beta-estradiol (E2) on synaptic transmission that results in both inhibition and excitation of gonadotropin releasing hormone (GnRH) neurons. Our hypothesis is that prolonged exposure to preovulatory levels of E2 enhances excitatory synaptic input and attenuates inhibitory synaptic input onto GnRH neurons, which ultimately facilitates bursting activity and peptide release. The first experiments will test the hypothesis that E2 will decrease the inhibitory input and increase the excitatory input to GnRH neurons after a period of at least 24 h. Tissues will be prepared from ovariectomized, estrogen- and oil-treated females at 1, 24, 36, and 40 h after treatment. Inhibitory neurotransmitter agonists (and antagonists) selective for mu-opioid and GABAB receptors will be tested on POA neurons and the underlying conductances which they activate characterized using sharp electrode recording. Excitatory neurotransmitter agonists (and antagonists) selective for alpha1-noradrenergic and glutamate receptors will be tested and the underlying conductances which they activate characterized in POA (GnRH) neurons. Focal electrical stimulation of afferent pathways into the POA will be done to identify inhibitory and excitatory synaptic currents using whole-cell patch recording. The second experiments will test the hypothesis that preovulatory levels of E2 will increase the intrinsic conductances underlying phasic bursting activity in GnRH neurons. Tissues will be prepared from ovariectomized, estrogen- and oil-treated females at 42 h after treatment. The expression of calcium T-current and the small conductance, calcium-dependent K+ (SK) current will be measured using single-electrode voltage clamp and in situ hybridization. In addition, the expression of the hyperpolarization-activated, non-selective cation current (Ih) will be measured using single-electrode voltage clamp. Lastly, the biocytin-injected neurons will be analyzed using histochemical techniques combined with confocal microscopy to elucidate the transmitter phenotype of the biocytin-injected neurons and their anatomical interaction with other neurons. The results from these studies will provide important new information about the mechanism by which estrogen alters the responsiveness of hypothalamic (GnRH) neurons, and how estrogens in general modify synaptic plasticity in the mammalian brain.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS035944-01A1
Application #
2411283
Study Section
Neurological Sciences Subcommittee 1 (NLS)
Program Officer
Kitt, Cheryl A
Project Start
1997-06-01
Project End
2001-03-31
Budget Start
1997-06-01
Budget End
1998-03-31
Support Year
1
Fiscal Year
1997
Total Cost
Indirect Cost
Name
Oregon Health and Science University
Department
Physiology
Type
Schools of Medicine
DUNS #
009584210
City
Portland
State
OR
Country
United States
Zip Code
97239
Ronnekleiv, Oline K; Kelly, Martin J (2005) Diversity of ovarian steroid signaling in the hypothalamus. Front Neuroendocrinol 26:65-84
Zheng, Shi-Xi; Bosch, Martha A; Ronnekleiv, Oline K (2005) mu-opioid receptor mRNA expression in identified hypothalamic neurons. J Comp Neurol 487:332-44
Kelly, Martin J; Qiu, Jian; Ronnekleiv, Oline K (2005) Estrogen signaling in the hypothalamus. Vitam Horm 71:123-45
Malyala, Anna; Pattee, Patrick; Nagalla, Srinivasa R et al. (2004) Suppression subtractive hybridization and microarray identification of estrogen-regulated hypothalamic genes. Neurochem Res 29:1189-200
Jamali, Khalid; Naylor, Barry R; Kelly, Martin J et al. (2003) Effect of 17beta-estradiol on mRNA expression of large- conductance, voltage-dependent, and calcium-activated potassium channel alpha and beta subunits in guinea pig. Endocrine 20:227-37
Qiu, Jian; Bosch, Martha A; Tobias, Sandra C et al. (2003) Rapid signaling of estrogen in hypothalamic neurons involves a novel G-protein-coupled estrogen receptor that activates protein kinase C. J Neurosci 23:9529-40
Kelly, Martin J; Qiu, Jian; Ronnekleiv, Oline K (2003) Estrogen modulation of G-protein-coupled receptor activation of potassium channels in the central nervous system. Ann N Y Acad Sci 1007:6-16
Slugg, Robert M; Zheng, Shi-Xi; Fang, Yuan et al. (2003) Baclofen inhibits guinea pig magnocellular neurones via activation of an inwardly rectifying K+ conductance. J Physiol 551:295-308
Ibrahim, Nurhadi; Bosch, Martha A; Smart, James L et al. (2003) Hypothalamic proopiomelanocortin neurons are glucose responsive and express K(ATP) channels. Endocrinology 144:1331-40
Kelly, Martin J; Qiu, Jian; Wagner, Edward J et al. (2002) Rapid effects of estrogen on G protein-coupled receptor activation of potassium channels in the central nervous system (CNS). J Steroid Biochem Mol Biol 83:187-93

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