Effects of mirtazapine on sleep disturbance under neuropathic pain-like state.

Sleep disturbance has been reported to be one of the most frequent symptoms in patients suffered from severe pain. Benzodiazepines are effective and reduce anxiety in the hours after use, but the induced sleep tends to be less than ideal in quality, with increased Stages I-II and reduces Stages III-IV sleep. In the present study, we investigated sleep disturbance under a neuropathic pain-like state in mice using electroencephalogram (EEG)/electromyogram (EMG). In a model of neuropathic pain, sciatic nerve ligation caused a marked decrease in the latency of paw withdrawal in response to a thermal stimulus only on the ipsilateral side. Under this condition, sciatic nerve-ligated animals showed a statistically significant increase in wakefulness and a decrease in non-rapid eye movement (NREM) sleep during the light phase. Mirtazapine (MTZ) is an antidepressant, which is considered to enhance noradrenergic and serotonergic neurotransmission via antagonistic action at central α2-adrenergic autoreceptors and heteroreceptors. In the present binding study, MTZ showed higher affinity for histamine H₁ and serotonin 5-HT(2A/2C) receptors than other receptors, including α2-adrenergic receptor, in the mouse brain tissue. The thermal hyperalgesia and sleep disturbance following nerve ligation were almost completely alleviated by MTZ. These findings suggest that MTZ may improve the quality of sleep as well as control pain in patients with neuropathic pain mainly through histamine H₁- and serotonin 5-HT₂-receptor antagonistic actions.