Neuroscience
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There is increasing evidence that alterations in the focus of attention result in changes in neural responding at the most peripheral levels of the auditory system. To date, however, those studies have not ruled out differences in task demands or overall arousal in explaining differences in responding across intermodal attentional conditions. The present study sought to compare changes in the response of cochlear outer hair cells, employing distortion product otoacoustic emissions (DPOAEs), under different, balanced conditions of intermodal attention. ⋯ Also consistent with our previous findings, DPOAE rapid adaptation, believed to be mediated by the medial olivocochlear efferents (MOC), was unaffected by changes in intermodal attention. The present findings indicate that manipulations in the conditions of attention, through the corticofugal pathway, and its last relay to cochlear outer hair cells (OHCs), the MOC, alter cochlear sensitivity to sound. These data also suggest that the MOC influence on OHC sensitivity is composed of two independent processes, one of which is under attentional control.
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Brief noxious heat stimuli activate Aδ- and C-fibers and allow contact heat-evoked potentials (CHEPs) to be recorded from the scalp. Under normal conditions, only late responses related to Aδ-fibers can be recorded. This study aimed to demonstrate C-fiber responses to contact heat stimuli. ⋯ Following nerve compression and capsaicin application, ultralate CHEPs with latencies >800 ms could be recorded in 13 subjects (62%), pain intensity to the contact heat stimuli was increased and the warm/hot-burning pain quality became more intense. The main results of our study are the demonstration of ultralate C-fiber-related CHEPs following A-fiber blockade in 29% of healthy subjects increasing to 62% when the blockade was combined with capsaicin. After blockade of Aδ-fibers we recorded responses with latencies in the range between the latencies of Aδ- and C-fibers suggesting release of Aδ-fibers with slower conduction velocity than normally recorded with CHEPs.
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In the present study, we aimed to identify whether cross-modal priming effect based on short-term experience of ecologically unrelated audio-visual information existed. In the experiment, we employed ecologically unrelated pictures and sounds as visual and auditory stimuli. ⋯ Enhanced induced gamma-band activity (GBA) was also found under the Match condition, and we suggested that induced GBA reflected the association between auditory and visual information to form supra-modal representation, which is top-down modulated by short-term experience of audio-visual information. Event-related potential (ERP) analysis revealed an N400 effect under the Mismatch condition compared to the Match condition, and source reconstruction of N400 effect showed that the biggest difference of activity between two conditions was localized in middle temporal gyrus (MTG), suggesting that MTG played an important role in the mapping process of auditory information onto a temporal semantic network.
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Astrocytes perform several functions that are essential for normal neuronal activity. They play a critical role in neuronal survival during ischemia and other degenerative injuries and also modulate neuronal recovery by influencing neurite outgrowth. In this study, we investigated the neuroprotective effects of astrocyte-derived 14,15-epoxyeicosatrienoic acid (14,15-EET), metabolite of arachidonic acid by cytochrome P450 epoxygenases (CYP), against oxidative stress induced by hydrogen peroxide (H(2)O(2)). ⋯ However, pretreatment with the CYP epoxygenase inhibitor miconazole (1-20 μM, 1h) before H(2)O(2) (1mM, 1h) stimulation showed decreased cell viability. Our data suggest that 14,15-EET which is released from astrocytes, enhances cell viability against oxidant-induced injury. Further understanding of the mechanism of 14,15-EET-mediated protection in dopaminergic neurons is imperative, as it could lead to novel therapeutic approaches for treating CNS neuropathologies, such as Parkinson's disease.
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Although many physiological adaptations of diving mammals have been reported, little is known about how their brains sustain the high demands for metabolic energy and thus O(2) when submerged. A recent study revealed in the deep-diving hooded seal (Cystophora cristata) a unique shift of the oxidative energy metabolism and neuroglobin, a respiratory protein that is involved in neuronal hypoxia tolerance, from neurons to astrocytes. Here we have investigated neuroglobin in another pinniped species, the harp seal (Pagophilus groenlandicus), and in two cetaceans, the harbor porpoise (Phocoena phocoena) and the minke whale (Balaenoptera acutorostrata). ⋯ Thus neuroglobin appears to play a specific role in diving mammals, but seals and whales have evolved divergent strategies to cope with cerebral hypoxia. The specific function of neuroglobin that conveys hypoxia tolerance may either relate to oxygen supply or protection from reactive oxygen species. The different strategies in seals and whales resulted from a divergent evolution and an independent adaptation to diving.