Neuroscience
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The present study examined if repeated bouts of micro- and hypergravity during parabolic flight (PF) alter structural integrity of the neurovascular unit (NVU) subsequent to free radical-mediated changes in regional cerebral perfusion. Six participants (5♂, 1♀) aged 29 ± 11 years were examined before, during and after a 3 h PF and compared to six sex and age-matched (27 ± 6 years) normogravity controls. Blood flow was measured in the anterior (middle cerebral artery, MCA; internal carotid artery, ICA) and posterior (vertebral artery, VA) circulation (duplex ultrasound) in-flight over the course of 15 parabolas. ⋯ Increased oxidative-nitrosative stress defined by a free radical-mediated reduction in NO and elevations in glio-vascular GFAP and S100ß were observed after PF (P < 0.05), the latter proportional to the increase in VA flow (r = 0.908, P < 0.05). In contrast, biomarkers of neuronal-axonal damage (neuron-specific enolase, neurofilament light-chain, ubiquitin carboxy-terminal hydrolase L1 and tau) did not change (P > 0.05). Collectively, these findings suggest that the cumulative effects of repeated gravitational transitions may promote minor blood-brain barrier disruption, potentially related to the combined effects of haemodynamic (posterior cerebral hyperperfusion) and molecular (systemic oxidative-nitrosative) stress.
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The allocation of attention to specific target stimuli is key to pursue a task successfully and attain a goal in an environment that is full of distractions and competing stimuli. Area 8A in the caudal dorsolateral prefrontal cortex is considered a central area for the top-down control of attention and lesion studies in both human and non-human primates have demonstrated that this area is critical for the successful selection of targets according to internal rules. ⋯ Both parts of area 8A share connections with the parietal multimodal higher order spatial processing region. The present functional neuroimaging study demonstrates that (a) frontal area 8A is critical for the rule-based attentional selection between alternative stimuli that face the individual and (b) that there is a functional dissociation between dorsal area 8A involved in the attentional selection of auditory stimuli and ventral area 8A in the selection of visual stimuli.
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Astrocyte dysfunction, and in particular impaired extracellular potassium spatial buffering, has been postulated to have a potential role in seizure susceptibility and ictogenesis. Inwardly rectifying potassium (Kir) channels, and specifically KIR4.1, have a predominant role in K+ homeostasis and their involvement in neuronal excitability control have been hypothesized. To avoid the severe side effects observed in Kir4.1 cKO, we studied the effects of Kir4.1 down-regulation in cortical astrocytes by using Kir4.1 RNA interference (RNAi) technique combined with in utero electroporation (IUE) at E16 and a piggyBac transposon system. ⋯ Intriguingly, immunohistochemical analysis performed on slices studied with electrophysiology revealed a reduced number of neurons generated from radial glial cells in Kir4.1- rats. We conclude that focal down-regulation of Kir4.1 channel in cortical astrocytes by Kir4.1 RNAi technique combined with IUE is not effective in altering potassium homeostasis and seizure susceptibility. This technique revealed a possible role of Kir4.1 during corticogenesis.
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Animal studies suggest that the vestibular system autoregulates its sensitivity in response to prolonged low- or high-intensity motion in order to maintain an optimal working range. In humans, corresponding attenuations of vestibular responses after prolonged high-intensity motion exposure have been demonstrated. Here we explored whether a complementary increase in human vestibular sensitivity can be induced by motion conditioning at low-intensity, subliminal amplitudes. ⋯ Vestibular sensitivity for yaw rotations remained on average unaltered after IA conditioning indicating that sensitizing effects might be selective for the end-organ-specific vestibular pathways being stimulated during conditioning. These findings demonstrate that human vestibular sensitivity can be enhanced by subliminal sensory conditioning, similar to sensitizing effects observed in other sensory modalities. Conditioning-induced sensitization of vestibular responses may be an effective treatment for decrements in vestibular sensitivity in the elderly and patients with vestibular hypofunction.
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In contrast to other rhythmic tasks such as running, the preferred movement rate in cycling does not minimize energy consumption. It is possible that neurophysiological mechanisms contribute to the choice of cadence, however this phenomenon is not well understood. Eleven participants cycled at a fixed workload of 125 W and different cadences including a freely chosen cadence (FCC, ∼72), and fixed cadences of 70, 80, 90 and 100 revolutions per minute (rpm) during which transcranial magnetic stimulation (TMS) was used to measure short interval intracortical inhibition (SICI) and intracortical facilitation (ICF). ⋯ Inhibition-excitation ratio (SICI divided by ICF) declined (P = 0.014) with an increase in cadence. The results demonstrate that SICI is attenuated during FCC compared to fixed cadences. The outcomes suggest that the attenuation of intracortical inhibition and augmentation of ICF may be a contributing factor for FCC.