Effects of diazepam and flumazenil on forebrain ischaemia in a rat model of benzodiazepine tolerance.

BACKGROUND Post-ischaemic benzodiazepine administration is neuroprotective, but chronic administration of benzodiazepines can induce tolerance, such that the neuroprotective effect may be reduced. This study investigated whether benzodiazepine tolerance can worsen ischaemic injury and whether neuroprotection by post-ischaemic benzodiazepine administration is affected by benzodiazepine tolerance. We also investigated whether antagonism of benzodiazepine receptors by flumazenil was able to restore neuroprotection during benzodiazepine tolerance. METHODS Experiments were performed in both benzodiazepine-tolerant and naive rats. Benzodiazepine tolerance was indeed by 4 weeks administration of flurazepam. Bilateral carotid artery occlusion (BCAO) was performed to cause cerebral ischaemia. Four experiments were performed: (1) BCAO with no further interventions; (2) BCAO followed by administration of diazepam; (3) administration of flumazenil before BAO; and (4) administration of flumazenil before and diazepam after BCAO. Neurological and histological assessment was performed 5 days after BCAO. RESULTS Benzodiazepine tolerance did not affect neuronal injury in the CA1 and CA3 regions and dentate gyrus of the hippocampus after severe ischaemic insult, but did worsen neuronal damage when mild ischaemia was applied (P<0.05). Neuroprotective efficacy of post-ischaemic diazepam was not observed under conditions of benzodiazepine tolerance. Flumazenil treatment before BCAO reduced ischaemic neuronal damage exacerbated by benzodiazepine tolerance (P<0.05), and restored neuroprotection by post-ischaemic diazepam (P<0.05), the effect of which was reduced by benzodiazepine tolerance (P<0.05). However, pre-ischaemic flumazenil treatment in naive animals reduced neuroprotection provided by post-ischaemic diazepam (P<0.01-0.05). CONCLUSIONS Benzodiazepine tolerance can worsen ischaemic neuronal injury and abolish the neuroprotection provided by post-ischaemic diazepam. Pre-treatment with flumazenil treatment reversed benzodiazepine tolerance and restored neuroprotection by post-ischaemic diazepam. These findings may suggest that management of patient's risk of developing cerebral ischaemia may need to take into account current use.