Transient Plasticity of Hippocampal CA1 Neuron Glutamate Receptors Contributes to Benzodiazepine Withdrawal-Anxiety

Abstract

Withdrawal from 1-week oral administration of the benzodiazepine (BZ), flurazepam (FZP) is associated with enhanced AMPA receptor (AMPAR)-mediated and reduced NMDA receptor (NMDAR)-mediated excitation in CA1 pyramidal neurons 2-days after cessation of FZP administration. The present study examined temporal regulation of glutamate receptor-mediated whole-cell currents in CA1 neurons from hippocampal slices prepared from 0-, 1-, 2-, and 4-day FZP-withdrawn rats in relation to expression of anxiety-like behavior during BZ withdrawal. AMPAR-mediated miniature excitatory postsynaptic current (mEPSC) amplitude was significantly increased in CA1 neurons from 1-and 2-day FZP-withdrawn rats, while evoked NMDAR EPSC amplitude was reduced only in neurons from 2-day FZP-withdrawn rats. Withdrawal-anxiety, measured in the elevated plus-maze, was observed 1 day, but not 0, 2, or 4 days, after FZP treatment with 1-day withdrawn rats spending significantly reduced time in open arms compared to controls. CA1 neuron hyperexcitability was evident from the significant increase in the frequency of extracellular, 4-AP-induced spike discharges in slices from 1-day FZP-withdrawn rats. Systemic injection of the NMDAR antagonist MK-801 (0.25 mg/kg) on day 1 of withdrawal prevented reduced NMDAR-mediated currents in CA1 neurons from 2-day FZP-withdrawn rats, whereas AMPAR-mediated currents remained upregulated. Furthermore, MK-801 'unmasked' withdrawal-anxiety in the same 2-day FZP-withdrawn rats. Systemic injection of the AMPAR antagonist GYKI-52466 (0.5 mg/kg) at the onset of withdrawal blocked increased AMPAR-mediated currents and withdrawal-anxiety in 1-day FZP-withdrawn rats. These findings suggest that increased CA1 neuron AMPAR-mediated excitation may contribute to hippocampal hyperexcitability and expression of withdrawal-anxiety after prolonged BZ exposure via NMDAR-mediated neural circuits.

Differential Effects of Two Chronic Diazepam Treatment Regimes on Withdrawal Anxiety and AMPA Receptor Characteristics

“…This is further supported by recent mouse studies in our laboratories in which there was an increase in AMPA receptor binding in the hippocampus following a single withdrawal from chronic DZP (Allison et al, 2005). These data are also consistent with evidence of increased AMPA binding in the hippocampus 48 h following cessation of 7-day chronic treatment with high doses of flurazepam and increases in hippocampal AMPA receptormediated transmission and withdrawal anxiety 24 h following flurazepam withdrawal (Van Sickle et al, 2004). Furthermore, 96 h following a chronic escalating dose regime (5-20 mg/kg oral DZP three times per day), withdrawal anxiety and increases in hippocampal and cortical GluR1 subunit mRNA and protein occurred (Izzo et al, 2001).…”

“…One group has suggested differential involvement of NMDA and AMPA receptors in DZP withdrawal, with AMPA receptor mechanisms being critical for initiating the withdrawal symptoms , akin to their role in other forms of synaptic activity such as LTP. While additionally, evidence from studies in which large doses of BZs have been administered has provided further support for the involvement of alterations in AMPA receptor properties, particularly in the hippocampus, following BZ withdrawal (Izzo et al, 2001;Van Sickle et al, 2004).…”

Regulation of GABAAReceptor Subunit Expression by Pharmacological Agents

“…Cerebral cortical GluN1 and GluN2B, but not GluN2A subunits of NMDA receptors (Tsuda et al, 1998), glutamic acid decarboxylase (GAD 67 ), and GluA1 subunit of AMPA receptor were increased in diazepamwithdrawn rats (Izzo et al, 2001). In rats withdrawn from flurazepam, amplitudes of AMPA receptor-mediated miniature excitatory postsynaptic currents were increased in hippocampal CA1 neurons (Van Sickle et al, 2004;Xiang and Tietz, 2007). The 50% enhancement in AMPA receptor function was attributed to an increase in GluA1 polypeptide trafficking from the endoplasmic reticulum and its subsequent incorporation into membranes (Song et al, 2007;Das et al, 2008), whereas NMDA receptor-mediated currents were reduced in this brain region (Van Sickle et al, 2004;Xiang and Tietz, 2007).…”

“…In rats withdrawn from flurazepam, amplitudes of AMPA receptor-mediated miniature excitatory postsynaptic currents were increased in hippocampal CA1 neurons (Van Sickle et al, 2004;Xiang and Tietz, 2007). The 50% enhancement in AMPA receptor function was attributed to an increase in GluA1 polypeptide trafficking from the endoplasmic reticulum and its subsequent incorporation into membranes (Song et al, 2007;Das et al, 2008), whereas NMDA receptor-mediated currents were reduced in this brain region (Van Sickle et al, 2004;Xiang and Tietz, 2007). Mice deficient in GluA1 subunits have reduced short-term tolerance (i.e., prolonged short-term impairment to high doses of flurazepam) and develop less tolerance but show increased withdrawal signs after a 7-day flurazepam treatment and challenge with flumazenil (Aitta-Aho et al, 2009).…”

Mechanisms of Action and Persistent Neuroplasticity by Drugs of Abuse

“…Whereas the increase in AMPAR function could not be abolished by the NMDAR antagonist dizocipline (MK-801), it was abolished by the L-type VGCC blocker nimodipine, which also reversed withdrawal anxiety. At day 2 of withdrawal, the levels of GluN1 and GluN2B subunits and NMDAR function were also downregulated, which could be reversed by blocking AMPARs and their upregulation (Van Sickle et al, 2004;Xiang and Tietz, 2007), suggesting that the change in AMPAR was the primary alteration in the glutamate system in BZ tolerance. These results 938 demonstrate an important cascade of transient (1-4 days) functionally interrelated changes in the hippocampal neurons that are caused by chronic, but not acute , BZ administration.…”