Brain research
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Transcranial direct current stimulation (tDCS) has been suggested as a therapeutic tool for pain syndromes. Although initial results in human subjects are encouraging, it still remains unclear whether the effects of tDCS can reverse maladaptive plasticity associated with chronic pain. To investigate this question, we tested whether tDCS can reverse the specific behavioral effects of chronic stress in the pain system, and also those indexed by corticosterone and interleukin-1β levels in serum and TNFα levels in the hippocampus, in a well-controlled rat model of chronic restraint stress (CRS). ⋯ This model of CRS proved effective to induce chronic pain, as the animals exhibited hyperalgesia and mechanical allodynia. The hot plate test showed an analgesic effect, and the von Frey test, an anti-allodynic effect after the last tDCS session, and there was a significant decrease in hippocampal TNFα levels. These results support the notion that tDCS reverses the detrimental effects of chronic stress on the pain system and decreases TNFα levels in the hippocampus.
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Mammals express ∼20 different connexins, the main gap junction forming proteins in mammals, and 3 pannexins, homologs of innexins, the main gap junction forming proteins in invertebrates. In both classes of gap junction, each channel is formed by two hemichannels, one contributed by each of the coupled cells. There is now general, if not universal, agreement that hemichannels of both classes can open in response to various physiological and pathological stimuli when they are not apposed to another hemichannels and face the external milieu. ⋯ Astrocytes release ATP and glutamate which can kill neurons in co-culture through activation of neuronal pannexin hemichannels. These studies implicate two kinds of gap junction hemichannel in inflammatory responses and cell death. This article is part of a Special Issue entitled Electrical Synapses.
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Electrical synaptic transmission via gap junctions has become an accepted feature of neuronal communication in the mammalian brain, and occurs often between dendrites of interneurons in major brain structures, including the hippocampus. Electrical and dye-coupling has also been reported to occur between pyramidal cells in the hippocampus, but ultrastructurally-identified gap junctions between these cells have so far eluded detection. Gap junctions can be formed by nerve terminals, where they contribute the electrical component of mixed chemical/electrical synaptic transmission, but mixed synapses have only rarely been described in mammalian CNS. ⋯ A high percentage of Cx36-positive puncta in the stratum lucidum was localized to mossy fiber terminals, as indicated by co-localization of Cx36-puncta with the mossy terminal marker vesicular glutamate transporter-1, as well as with other proteins that are highly concentrated in, and diagnostic markers of, these terminals. These results suggest that mossy fiber terminals abundantly form mixed chemical/electrical synapses with pyramidal cells, where they may serve as intermediaries for the reported electrical and dye-coupling between ensembles of these principal cells. This article is part of a Special Issue entitled Electrical Synapses.
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Tinnitus perception depends on the presence of its neural correlates within the auditory neuraxis and associated structures. Targeting specific circuits and receptors within the central nervous system in an effort to relieve the perception of tinnitus and its impact on one's emotional and mental state has become a focus of tinnitus research. One approach is to upregulate endogenous inhibitory neurotransmitter levels (e.g., glycine and GABA) and selectively target inhibitory receptors in key circuits to normalize tinnitus pathophysiology. ⋯ Finally, some selective compounds, which enhance tonic inhibition, have successfully ameliorated tinnitus in animal studies, suggesting that the MGB and, to a lesser degree, the auditory cortex may be their primary locus of action. These pharmacological interventions are examined in terms of their mechanism of action and why these agents may be effective in tinnitus treatment. This article is part of a Special Issue entitled: Tinnitus Neuroscience.
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Thirteen chronic tinnitus patients and fifteen age-matched healthy controls were studied on a 3T magnetic resonance imaging (MRI) scanner during resting condition (i.e. eyes closed, no task performance). The auditory resting-state component was selected using an automatic component selection approach. Functional connectivity (correlations/anti-correlations) in the extracted network was portrayed by integrating the independent component analysis (ICA) approach with a graph theory method. ⋯ Our results show a modified functional connectivity pattern in tinnitus sufferers and highlight the role of the parahippocampal region in tinnitus physiopathology. They also point out the importance of the activity and connectivity pattern of the posterior cingulate cortex/precuneus region to the development of the tinnitus associated distress. This article is part of a Special Issue entitled: Tinnitus Neuroscience.