Glutamate is the major fast excitatory neurotransmitter in most regions of the central nervous system (CNS), including the hypothalamus. A decreased level of glutamate activity can be found during the use of antiglutamate receptor drugs (including some drugs of abuse), selective degeneration of glutamatergic neurons or projections, and embryonic development. Observations from other laboratories revealed increased cholinergic functions in the CNS during each of these three conditions. Our recent experiments in hypothalamic neuronal cultures indicated that a chronic blockade of ionotropic glutamate receptors dramatically increases excitatory acetylcholine (ACh) synaptic activity and the number of cholinergic neurons. Data suggested that during a long-term decrease in glutamate transmission in the hypothalamus in vitro, ACh, which normally exhibits only weak activity in the hypothalamus, plays the role of the major excitatory neurotransmitter and supports the excitation/inhibition balance. We also hypothesized that an increase in excitatory ACh transmission represents a novel form of neuronal plasticity that regulates the activity and excitability in neurons during a decrease in glutamate excitation. However, the mechanisms of glutamate-dependent regulation of ACh transmission in the CNS have not been studied. They will be studied in the proposed research in hypothalamic neurons. First, using rat hypothalamic cultures, we will test the hypothesis that during decrease in glutamate transmission ACh and glutamate are co-released from the same synaptic terminals. Second, using hypothalamic cultures, we will test the hypothesis that the induction of cholinergic phenotype in neurons is regulated through a CREB-dependent signal transduction pathway. Third, we will test the prediction that a chronic blockade of glutamate NMDA receptors in rats in vivo increases cholinergic phenotypic properties in hypothalamic neurons. This will be studied using electrophysiology, Ca 2+ imaging, immunostaining, and molecular biology. This project addresses the fundamental mechanisms of neuronal plasticity and regulation of neuronal activity that can take place in neuronal circuits during a decrease in glutamate excitation. Data obtained here may have an important clinical relevance, given that glutamate receptor antagonists are used for chronic treatment of patients, and some glutamate receptor antagonists are drugs of abuse.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA015088-03
Application #
7006973
Study Section
Special Emphasis Panel (ZRG1-BDCN-2 (01))
Program Officer
Wu, Da-Yu
Project Start
2004-03-01
Project End
2009-12-31
Budget Start
2006-01-01
Budget End
2006-12-31
Support Year
3
Fiscal Year
2006
Total Cost
$181,264
Indirect Cost
Name
Tulane University
Department
Anatomy/Cell Biology
Type
Schools of Arts and Sciences
DUNS #
053785812
City
New Orleans
State
LA
Country
United States
Zip Code
70118
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Michaelis, E K; Wang, X; Pal, R et al. (2011) Neuronal Glud1 (glutamate dehydrogenase 1) over-expressing mice: increased glutamate formation and synaptic release, loss of synaptic activity, and adaptive changes in genomic expression. Neurochem Int 59:473-81
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Bao, Xiaodong; Pal, Ranu; Hascup, Kevin N et al. (2009) Transgenic expression of Glud1 (glutamate dehydrogenase 1) in neurons: in vivo model of enhanced glutamate release, altered synaptic plasticity, and selective neuronal vulnerability. J Neurosci 29:13929-44
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Liu, Xinhuai; Popescu, Ion R; Denisova, Janna V et al. (2008) Regulation of cholinergic phenotype in developing neurons. J Neurophysiol 99:2443-55
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de Rivero Vaccari, Juan Carlos; Corriveau, Roderick A; Belousov, Andrei B (2007) Gap junctions are required for NMDA receptor dependent cell death in developing neurons. J Neurophysiol 98:2878-86
Leininger, Eric; Belousov, Andrei B (2006) Homeostatic plasticity: comparing and contrasting cortical and hippocampal studies. A review. Crit Rev Neurobiol 18:125-34

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