Hypersusceptibility to DMCM-induced seizures during diazepam withdrawal in mice: evidence for upregulation of NMDA receptors

Abstract

The present study investigated the role of NMDA (N-methyl-D-aspartate) receptors in the hypersusceptibility to seizures induced by the benzodiazepine inverse agonist DMCM (methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate) during diazepam withdrawal in mice, using behavioral and biochemical approaches. The seizure threshold of DMCM was markedly decreased during diazepam withdrawal, reflecting withdrawal hyperexcitability in response to physical dependence. The decrease in the seizure threshold of DMCM in diazepam-withdrawn mice was inhibited by the non-competitive NMDA receptor antagonists MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cycloheptan-5,10-imine maleate; 50 microg/kg, s.c.) and ifenprodil (20 mg/kg, i.p.). The effective doses of these compounds were lower than those required to prevent DMCM-induced seizures in chronically vehicle-treated mice. Since MK-801 and ifenprodil do not only bind to NMDA receptors but also to sigma receptors, the present study also investigated the effects of sigma receptor ligands. The decrease in the seizure threshold of DMCM in diazepam-withdrawn mice was not modified by the sigma receptor agonist, (+)-pentazocine (5 mg/kg, s.c.), or the sigma receptor antagonist, NE-100 (N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride; 5 mg/kg, i.p.). Furthermore, the latency to the expression of wild running induced by intracerebroventricular administration of NMDA (60 ng/mouse) was also significantly lower in diazepam-withdrawn mice than in vehicle-treated control mice. On the other hand, there was no difference in the spermidine concentration between vehicle-treated control and diazepam-withdrawn mice. In a receptor binding experiment, the Bmax value for [3H]-MK-801 binding was significantly increased in cerebrocortical tissues from diazepam-withdrawn mice, while the Kd value did not change in either group. However, the acute addition of a high concentration of diazepam (10 and 100 microM) in vitro did not alter [3H]-MK-801 binding in cerebrocortical membrane preparations. The behavioral experiments suggest that NMDA receptor antagonists may suppress benzodiazepine withdrawal responses, while the biochemical study reveals upregulation of the NMDA receptor, which may play an important role in the hypersusceptibility to DMCM-induced seizure in diazepam-withdrawn mice.

Involvement of the K+‐Cl− co‐transporter KCC2 in the sensitization to morphine‐induced hyperlocomotion under chronic treatment with zolpidem in the mesolimbic system

“…Previous reports suggested that withdrawal after chronic treatment with diazepam increased [ 3 H]MK801 binding and NR1 and NR2B NMDA receptor subunit protein in rat cerebrocortical tissue (Tsuda et al . , b). Moreover, the GABA A R α1 subunit‐preferring benzodiazepine‐site ligand zolpidem also produced an increase in the AMPA/NMDA ratio in VTA dopamine neurons.…”

Up‐regulation of L‐type high voltage‐gated calcium channel subunits by sustained exposure to 1,4‐ and 1,5‐benzodiazepines in cerebrocortical neurons

“…Mice were intraperitoneally administered diazepam (16 mg/kg/day), brotizolam (16 mg/kg/day), and clobazam (16 mg/kg/day) for 5 days (Löscher et al. 1996; Tsuda et al. 1998) with a minor modification.…”

Chronic Exposure to Nitrous Oxide Increases [3H]MK801 Binding in the Cerebral Cortex, but Not in the Hippocampus of Adult Mice

“…Our study indicates region‐specific changes in [ 3 H]MK801 binding, for example, a significant increase in the number or affinity of binding sites in the cerebral cortex, but not in the hippocampus. Similarly, region‐specific upregulation of NMDA receptors in the cerebral cortex, but not in the hippocampus, has been described in studies of tolerance and withdrawal after chronic exposure to ethanol, benzodiazepines, or barbiturates 14‐18. The “peculiar interaction” between GABA A and NMDA receptors in the cerebral cortex may be responsible for this phenomenon 19.…”