Neuroscience
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We hypothesised that, since anomalous neck proprioceptive input can produce perturbing effects on posture, neck muscle fatigue could alter body balance control through a mechanism connected to fatigue-induced afferent inflow. Eighteen normal subjects underwent fatiguing contractions of head extensor muscles. Sway during quiet stance was recorded by a dynamometric platform, both prior to and after fatigue and recovery, with eyes open and eyes closed. ⋯ Contractions of the same duration, but not inducing EMG signs of fatigue, had much less influence on body sway or subjective scoring. We argue that neck muscle fatigue affects mechanisms of postural control by producing abnormal sensory input to the CNS and a lasting sense of instability. Vision is able to overcome the disturbing effects connected with neck muscle fatigue.
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Comparative Study
Kinetics of synaptic transfer from rods and cones to horizontal cells in the salamander retina.
We examined synaptic transmission between rods or cones and horizontal cells, using perforated patch recording techniques in salamander retinal slices. Experimental conditions were established under which horizontal cells received nearly pure rod or pure cone input. The response-intensity relation for both photoreceptors and horizontal cells was described by a Michaelis-Menten function with an exponent close to 1. ⋯ The good fit to the model confirms that these are the key features of synaptic transmission from rods and cones. The model accommodated changes in kinetics induced by the glutamate uptake blocker, dihydrokainate. The match between model and response was not improved by including an estimate of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor desensitization or by making glutamate uptake voltage dependent.
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Comparative Study
Stimulus-induced patterns of bioelectric activity in human neocortical tissue recorded by a voltage sensitive dye.
Stimulus-induced pattern of bioelectric activity in human neocortical tissue was investigated by use of the voltage sensitive dye RH795 and a fast optical recording system. During control conditions stimulation of layer I evoked activity predominantly in supragranular layers showing a spatial extent of up to 3000 microm along layer III. Stimulation in white matter evoked distinct activity in infragranular layers with a spatial extent of up to 3000 microm measured along layer V. ⋯ The activity pattern of those slices appeared atypical in regard to their deviations of the vertical and horizontal extent of activity, to their reduced spatial extent of activity during increased excitability, to their layer-related distribution of activity, and to the appearance of afterdischarges. Concluding, in 30% of the human temporal lobe slices atypical activity pattern occurred which obviously reflect intrinsic epileptiform properties of the resected tissue. The majority of slices showed stereotyped activity pattern without evidence for increased excitability.
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Comparative Study
Biochemical analysis of GABA(A) receptor subunits alpha 1, alpha 5, beta 1, beta 2 in the hippocampus of patients with Alzheimer's disease neuropathology.
Alzheimer's disease (AD) is characterized by selective vulnerability of specific neuronal populations within particular brain regions. For example, hippocampal glutamatergic cell populations within the CA1/subicular pyramidal cell fields have been found to be particularly vulnerable early in AD progression. In contrast, hippocampal GABA-ergic neurons and receptors appear resistant to neurodegeneration. ⋯ In particular, alpha 1, beta 1, and beta 2 displayed little difference in protein levels among pathologically mild, moderate, and severe subject groups. In contrast, although relatively modest, protein levels of the alpha 5 subunit were significantly reduced between subjects with severe neuropathology compared with pathologically mild subjects (13.5% reduction). Collectively, our data provide evidence for heterogeneous distribution and relative sparing of GABA(A) receptor subunits in the hippocampus of AD patients.
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The modulation of the firing discharge of medial septal neurons and of the hippocampal electroencephalogram (EEG) mediated by actions on alpha2-adrenoreceptors (ARs) was investigated in awake rabbits. Bilateral i.c.v. infusion of a relatively low dose (0.5 microg) of the alpha2-AR agonist clonidine produced a reduction in the theta rhythmicity of both medial septal neurons and the hippocampal EEG. In contrast, a high dose of clonidine (5 microg) increased the percentage and degree of rhythmicity of theta bursting medial septal neurons as well as the theta power of the hippocampal EEG. ⋯ These results suggest that low doses of alpha2-ARs agents may act at autoreceptors regulating the synaptic release of noradrenaline, while high doses of alpha2-ARs drugs may have a predominant postsynaptic action. Similar results were observed after local injection of the alpha2-AR drugs into the medial septum suggesting that the effects induced by the i.c.v. infusion were primarily mediated at the medial septal level. We suggest that noradrenergic transmission via the postsynaptic alpha2-ARs produces fast and strong activation of the septohippocampal system in situations that require urgent selective attention to functionally significant information (alert, aware), whereas the action via the presynaptic alpha2-ARs allows a quick return of the activity to the initial level.