Neuroscience letters
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Neuroscience letters · Jul 2017
Chronic exposure to tumor necrosis factor in vivo induces hyperalgesia, upregulates sodium channel gene expression and alters the cellular electrophysiology of dorsal root ganglion neurons.
The goal of these studies was to investigate the links between chronic exposure to the pro-inflammatory cytokine tumor necrosis factor (TNF), hyperalgesia and the excitability of dorsal root ganglion (DRG) sensory neurons. We employed transgenic mice that constitutively express TNF (TNFtg mice), a well-established model of chronic systemic inflammation. At 6 months of age, TNFtg mice demonstrated increased sensitivity to both mechanical and thermal heat stimulation relative to aged-matched wild-type controls. ⋯ Increased overlap of activation and inactivation in the TNFtg neurons produces inward Na+ currents at voltages near the resting membrane potential of sensory neurons (i.e. window currents). The combination of increased Na+ current amplitude, hyperpolarized shifts in Na+ channel activation and increased window current predicts a reduction in the action potential threshold and increased firing of small-diameter DRG neurons. Together, these data suggest that increases in the expression of Nav1.8 channels, regulatory β1 subunits and TNFR1 contribute to increased nociceptor excitability and hyperalgesia in the TNFtg mice.
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Neuroscience letters · Jul 2017
Suppressed neural complexity during ketamine- and propofol-induced unconsciousness.
Ketamine and propofol have distinctively different molecular mechanisms of action and neurophysiological features, although both induce loss of consciousness. Therefore, identifying a common feature of ketamine- and propofol-induced unconsciousness would provide insight into the underlying mechanism of losing consciousness. In this study we search for a common feature by applying the concept of type-II complexity, and argue that neural complexity is essential for a brain to maintain consciousness. ⋯ For the analysis, we use Mean Information Gain (MIG) and Fluctuation Complexity (FC), which are information-theory-based measures that quantify disorder and complexity of dynamics respectively. Both ketamine and propofol reduced the complexity of the EEG signal, but ketamine increased the randomness of the signal and propofol decreased it. The finding supports our claim and suggests EEG complexity as a candidate for a consciousness indicator.
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Neuroscience letters · Jul 2017
Decreased middle temporal gyrus connectivity in the language network in schizophrenia patients with auditory verbal hallucinations.
As the most common symptoms of schizophrenia, the long-term persistence of obstinate auditory verbal hallucinations (AVHs) brings about great mental pain to patients. Neuroimaging studies of schizophrenia have indicated that AVHs were associated with altered functional and structural connectivity within the language network. However, effective connectivity that could reflect directed information flow within this network and is of great importance to understand the neural mechanisms of the disorder remains largely unknown. ⋯ The results showed that the connection from the left inferior frontal gyrus (LIFG) to left middle temporal gyrus (LMTG) was significantly decreased in patients with AVHs compared to those without AVHs. Meanwhile, the effective connection from the left inferior parietal lobule (LIPL) to LMTG was significantly decreased compared to the healthy controls. Our findings suggest aberrant pattern of causal interactions within the language network in patients with AVHs, indicating that the hypoconnectivity or disrupted connection from frontal to temporal speech areas might be critical for the pathological basis of AVHs.