The neurophysiological mechanisms underlying withdrawal syndromes reflecting physical dependence on a variety of drugs of abuse, including the benzodiazepines (BZs), are unknown. Using a well-established rat model of chronic BZ treatment, we have identified changes in hippocampal excitatory amino acid receptors temporally associated with anxiety-like behavior, a sign of withdrawal. CA1 neuron changes include increases in alpha-amino-3-hydroxy-5-methyl-4-isozaxolepropionic acid receptor (AMPAR) current amplitude and conductance, and increases in AMPAR binding and GluR1 subunit levels. When AMPAR currents increase, N-methyl-D-aspartate receptor (NMDAR)-evoked currents, NMDA efficacy and NR2B subunit levels are reduced. NMDA antagonist treatment during withdrawal reverses NMDAR down regulation, allowing more prolonged expression of anxiety-like behavior. AMPAR antagonist treatment prevents subsequent AMPAR upregulation. These findings suggest that enhanced AMPAR function contributes to BZ-induced withdrawal through NMDAR-dependent hippocampal pathways, and are reminiscent of well-described mechanisms underlying activity-dependent plasticity of hippocampal excitatory synapses. Similar mechanisms may be involved in behavioral plasticity during BZ withdrawal. The working hypothesis is that localized remodeling of hippocampal CA1 neuron excitatory synapses is a central feature underlying BZ physical dependence, expressed as withdrawal-induced anxiety-like behavior, and has essential characteristics analogous to those associated with activity-dependent synaptic plasticity. Three specific hypotheses focus on the subunit dependence of the functional and structural alterations that occur at CA1 neuron EAAR synapses after withdrawal from 1-week flurazepam treatment. AMPA and NMDAR function will be studied at selected time-points after drug removal, when anxiety-like behavior is expressed, using whole-cell and outside-out patch techniques in hippocampal slices and acutely dissociated CA1 neurons.
The first aim will be to explore AMPAR channel properties using GluR1 subunit-selective neurophysiological and pharmacological tools.
The second aim will use a similar approach to study the NR2B-subunitdependence of decreased NMDAR function at CA1 synapses.
The third aim i s to use light microscopic and electron microscopic immunohistochemical approaches to investigate the structural changes in AMPARs and NMDARs at CA1 synapses that contribute to changes in hippocampal excitatory function and to anxiety-like behavior. Rational approaches to the treatment of physical dependence on drugs of abuse can emerge from a better understanding of the neurophysiological mechanisms underlying withdrawal phenomena.

Agency
National Institute of Health (NIH)
Institute
National Institute on Drug Abuse (NIDA)
Type
Research Project (R01)
Project #
5R01DA018342-04
Application #
7388792
Study Section
Neurobiology of Motivated Behavior Study Section (NMB)
Program Officer
Sorensen, Roger
Project Start
2005-04-01
Project End
2010-03-31
Budget Start
2008-04-01
Budget End
2009-03-31
Support Year
4
Fiscal Year
2008
Total Cost
$313,234
Indirect Cost
Name
University of Toledo
Department
Physiology
Type
Schools of Medicine
DUNS #
807418939
City
Toledo
State
OH
Country
United States
Zip Code
43614
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Earl, Damien E; Tietz, Elizabeth I (2011) Inhibition of recombinant L-type voltage-gated calcium channels by positive allosteric modulators of GABAA receptors. J Pharmacol Exp Ther 337:301-11
Shen, Guofu; Tietz, Elizabeth I (2011) Down-regulation of synaptic GluN2B subunit-containing N-methyl-D-aspartate receptors: a physiological brake on CA1 neuron ?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hyperexcitability during benzodiazepine withdrawal. J Pharmacol Exp Ther 336:265-73
Shen, Guofu; Van Sickle, Bradley J; Tietz, Elizabeth I (2010) Calcium/calmodulin-dependent protein kinase II mediates hippocampal glutamatergic plasticity during benzodiazepine withdrawal. Neuropsychopharmacology 35:1897-909
Das, Paromita; Zerda, Ricardo; Alvarez, Francisco J et al. (2010) Immunogold electron microscopic evidence of differential regulation of GluN1, GluN2A, and GluN2B, NMDA-type glutamate receptor subunits in rat hippocampal CA1 synapses during benzodiazepine withdrawal. J Comp Neurol 518:4311-28
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Xiang, K; Tietz, E I (2008) Chronic benzodiazepine-induced reduction in GABA(A) receptor-mediated synaptic currents in hippocampal CA1 pyramidal neurons prevented by prior nimodipine injection. Neuroscience 157:153-63
Xiang, Kun; Tietz, Elizabeth I (2007) Benzodiazepine-induced hippocampal CA1 neuron alpha-amino-3-hydroxy-5-methylisoxasole-4-propionic acid (AMPA) receptor plasticity linked to severity of withdrawal anxiety: differential role of voltage-gated calcium channels and N-methyl-D-aspartic acid re Behav Pharmacol 18:447-60
Song, Jun; Shen, Guofu; Greenfield Jr, L John et al. (2007) Benzodiazepine withdrawal-induced glutamatergic plasticity involves up-regulation of GluR1-containing alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors in Hippocampal CA1 neurons. J Pharmacol Exp Ther 322:569-81