Anesthesiology
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Cortical γ oscillations are thought to play a role in conscious cognitive functions. Suppression of 40-Hz γ activity was implicated in the loss of consciousness during general anesthesia. However, several experimental studies found that γ oscillations were preserved in anesthesia. The authors investigated the concentration-dependent effect of isoflurane on spontaneous γ oscillations in two frequency bands and three distinct brain regions in the rat. ⋯ Distinction between high- and low-frequency γ bands is important when evaluating the effect of general anesthetics on brain electrical activity. Spontaneous 40-Hz γ power does not indicate the state of consciousness. The attenuation and interregional desynchronization of high-frequency γ oscillations appear to correlate with the loss of consciousness.
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Opioids are powerful analgesics, but are also common drugs of abuse. Few studies have examined how neuropathic pain alters the pharmacology of opioids in modulating limbic pathways that underlie abuse liability. ⋯ Nerve injury suppressed potentiation of electrical stimulation of the ventral tegmental area by opioids, suggesting that the positive reinforcing effects are diminished by chronic pain. Given concerns regarding prescription opioid abuse, developing strategies that assess both analgesia and abuse liability within the context of chronic pain may aid in determining which opioids are most suitable for treating chronic pain when abuse is a concern.
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Neuropathic pain alters opioid self-administration in rats. The brain regions altered in the presence of neuropathic pain mediating these differences have not been identified, but likely involve ascending pain pathways interacting with the limbic system. The amygdala is a brain region that integrates noxious stimulation with limbic activity. ⋯ μ-Opioid receptors in the lateral amygdala partially meditate heroin's antiallodynic effects and self-administration after peripheral nerve injury. The lack of effect of β-funaltrexamine on heroin self-administration in sham-operated subjects suggests that opioids maintain self-administration through a distinct mechanism in the presence of pain.