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Bidirectional Regulation of AMPA and NMDA Receptors during Benzodiazepine Withdrawal

by Shen, Guofu

Abstract (Summary)
BZ withdrawal can lead to adaptive modification of glutamatergic synaptic transmission in hippocampal CA1 neurons. Two subtypes of glutamate receptors, AMPAR and NMDAR, showed different patterns of modification upon BZ withdrawal. The possible mechanisms and intrinsic relationship of these two receptors during BZ withdrawal were studied in this dissertation. AMPAR-mediated mEPSC amplitudes were increased 30% in CA1 neurons with a 2-fold increase in single-channel conductance. The potentiated AMPAR-mediated synaptic transmission was also manifested by an increased slope of the input-output curve. CaMKIIā€™s contribution to the potentiation was validated by pre-incubation of slices with the selective inhibitor, KN-93, or intracellular inclusion of AIP, both of which prevented the increases of AMPAR current amplitude and conductance. Increased NAS inhibition was consistent with synaptic incorporation of homomeric GluR1 AMPARs. In 1-day withdrawn rats, only GluR1 levels were increased in immunoblots of the PSD-enriched subcellular fraction from CA1 minislices consistent with increased mEPSC amplitude, but not conductance. In 2-day withdrawn rats, total, but not relative phospho-Thr286 CaMKII levels increased in the PSD-enriched subfraction in parallel with increased GluR1 and phospho-Ser831 GluR1 expression levels implying that CaMKII mediates AMPAR phosphorylation and increased channel conductance in FZP-withdrawn CA1 neurons. Whole-cell and field (f)EPSP recordings revealed that LTP expression, induced by low-intensity theta burst stimulation, was impaired in CA1 neurons from FZPwithdrawn rats although no memory deficits were detectable using a novelty preference paradigm. The findings suggest that synaptic insertion and subsequent CaMKII-mediated phosphorylation of homomeric GluR1 AMPARs might contribute to BZ withdrawalinduced potentiation of AMPARs analogous to mechanisms underlying activitydependent plasticity. NMDAR function was depressed during BZ withdrawal. The contribution of the NR2B subunit to NMDAR downregulation was indicated both by the effect of ifenprodil on NMDAR currents and by the decreased expression level of both NR1 and NR2B, but not NR2A subunits in PSD-enriched fractions from 2-day FZP-withdrawn rats. The depression of NMDAR currents was secondary to AMPAR potentiation, since AMPA incubation could accelerate the reduction in NMDAR currents in 1-day FZP withdrawn rat, and could counteract the hyperactivity of AMPAR when total charge transfer was measured. Calcium-related homeostatic regulation through calcium-permeable AMPARs and L-type voltage-gated calcium channels was proposed to explain the possible CaMKII/calmodulin-mediated mechanisms underlying the enhancement of AMPA and depression of NMDAR currents, and their relationship to the appearance of withdrawal anxiety.
Bibliographical Information:

Advisor:

School:University of Toledo Health Science Campus

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:benzodiazepine dependence ampa receptor nmda calcium calmodulin dependent kinase ii

ISBN:

Date of Publication:07/14/2009

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