Int Rev Neurobiol
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Methamphetamine (MAP), a drug of abuse known worldwide for its addictive effects and neurotoxicity, causes somatic and psychiatric disorders. MAP enters terminals/neurons via monoamine transporters, displaces both vesicular and intracellular monoamines, and facilitates the release of monoamines into the extraneuronal space through synaptic transport via the monoamine transporters. Chronic psychostimulant abusers exhibit psychotic features, including delusions and auditory hallucinations. ⋯ The deletion of DAT attenuates the locomotor effects of MAP and may play larger role in behavioral responses to MAP compared to the deletion of VMAT2. MAP produces hyperthermia and/or neuronal toxicity in most species. The effects of MAP in DAT or serotonin transporter (SERT) single knockout (KO) mice and DAT/SERT double KO mice suggested that DAT and SERT are key molecules for hyperthermia and neuronal toxicity of MAP.
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Neuropathic pain is one of the worst painful symptoms in clinic. It contains nerve-injured neuropathy, diabetic neuropathy, chronic inflammatory pain, cancer pain, and postherpes pain, and is characterized by a tactile allodynia and hyperalgesia. Neuropathic pain, especially the nerve-injured neuropathy, the diabetic neuropathy, and the cancer pain, is opioid resistant pain. ⋯ These drugs show remarkable effectiveness against hyperalgesia and allodynia during neuropathic pain states. Oxycodone is a mu-opioid receptor agonist, which has different pharmacological profiles with morphine. The remarkable effectiveness of oxycodone for neuropathic pain provides the possibility that mu-opioid receptor agonists, which have different pharmacological profile with morphine, can be used for the management of neuropathic pain.
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Experimental evidence suggests that reinnervation of the distal stump of a transected nerve may occur if the former is coapted end-to-side to the trunk of an adjacent nerve. Axonal regeneration occurs by collateral sprouting of healthy donor nerve axons, induced by neurotrophic factors. ⋯ End-to-side neurorrhaphy has already been used in the clinical practise, but there are still some issues that have not been completely clarified yet: (i) the origin of regenerating axons, (ii) collateral sprouting molecular mechanisms, and (iii) the degree of donor nerve axotomy needed for motor functional recovery. The results of experimental studies trying to investigate these parameters are briefly discussed in this review article.
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Morphine-3-glucuronide (M3G), a main metabolite of morphine, has been proposed as a responsible factor when patients present with the neuroexcitatory side effects (allodynia, hyperalgesia, and myoclonus) observed following systemic administration of large doses of morphine. Indeed, both high-dose morphine (60 nmol/5 microl) and M3G (3 nmol/5 microl) elicit allodynia when administered intrathecally (i.t.) into mice. The allodynic behaviors are not opioid receptor mediated. ⋯ Furthermore, the increased release of NO observed after i.t. injection of M3G activates astrocytes and induces the release of the proinflammatory cytokine, interleukin-1beta. Taken together, these findings suggest that M3G may induce allodynia via activation of NO-ERK pathway, while maintenance of the allodynic response may be triggered by NO-activated astrocytes in the dorsal spinal cord. The demonstration of the cellular mechanisms of neuronal-glial interaction underlying M3G-induced allodynia provides a fruitful strategy for improved pain management with high doses of morphine.
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Elucidation of the mechanism of neuropathic pain caused by vincristine is required because long-term treatment with this anticancer agent often causes neuropathic pain. We refer to the involvement of inflammatory mediators in vincristine-induced neuropathic pain in this review. Several reports using rodents have shown that long-lasting neuropathic pain (mechanical allodynia) is caused by repeated systemic injection of vincristine. ⋯ In the CNS, these inflammatory cytokines have an important role in the neuropathic pain caused by vincristine. Immune-modulating agents that prevent activation of immune cells and/or the inhibitory agents of inflammatory cytokines could prevent the neuropathic pain caused by vincristine. These agents could increase the tolerability of vincristine when used for the treatment of leukemia and lymphoma.