Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Loss of interhemispheric inhibition in patients with multiple sclerosis is related to corpus callosum atrophy.
Axonal injury and loss in the corpus callosum (CC) is characteristic of the pathology of multiple sclerosis (MS). Functional magnetic resonance imaging (fMRI) potentially allows neurophysiological consequences of this interhemispheric axonal loss to be defined quantitatively. Here we have used 3T fMRI to study the activation in the contralateral primary sensorimotor cortex and deactivation (mediated by transcallosal tracts) in the homologous ipsilateral region in 14 patients with MS and in 14 matched healthy controls during a simple hand-tapping task. ⋯ Atrophy of the CC was correlated with loss of deactivation for the whole patient group (r = -0.50, P = 0.035), but particularly for MS-phd (r = -0.914, P = 0.004). Interhemispheric physiological inhibition thus is impaired in patients with MS, potentially contributing to impairment of motor control. This work suggests one way in which FMRI monitoring of the transcallosal interactions in motor cortex could become a tool for evaluation of therapies that may enhance function in reversibly impaired pathways.
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Comparative Study
Topiramate and cortical excitability in humans: a study with repetitive transcranial magnetic stimulation.
Repetitive transcranial magnetic stimulation (rTMS) delivered at 5 Hz frequency and suprathreshold intensity progressively increases the size of muscle evoked potentials (MEPs) and the duration of the cortical silent period (CSP) in normal subjects. The aim of this study was to evaluate the effects of topiramate (TPM) at different doses on cortical excitability variables tested with rTMS. We tested the facilitation of the MEP size and CSP duration evoked by focal rTMS in eight patients before and after treatment with TPM at different doses for chronic neuropathic pain. ⋯ Our results suggest that TPM modulates the excitatory intracortical interneurons probably by altering rTMS-induced synaptic potentiation. These drug-induced effects are related to TPM doses and plasma concentrations. In conclusion, rTMS may be useful for quantifying the effectiveness of antiepileptic drugs and for assessing individual responses to different drugs but acting through similar mechanisms, thus combining functional neurophysiological information and laboratory data.
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Convergence between cutaneous heat nociceptors and muscles afferents was investigated by applying a phasic, conditioning electrical stimulus to the tibialis anterior muscle (a train of five 1 ms pulses over 21 ms) at varying time intervals relative to a thermal test stimulus used for evoking the withdrawal reflex in humans. The 200 ms thermal stimulus was applied on the dorsum of the foot at an intensity of two times the pain threshold. ⋯ The mean reflex onset latency of reflexes evoked by thermal stimuli alone was 354 +/- 9 ms. A facilitation of the reflex was seen when the conditioning stimulus was applied 275 ms (174 +/- 30% compared to control) and 300 ms (162 +/- 32% compared to control) after the test stimulus onset indicating sensory convergence between muscle afferents (group I-III) and cutaneous Adelta heat nociceptors arriving simultaneously at the spinal cord.
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Comparative Study
Effects of intracerebroventricular injections of free fatty acids, lysophospholipids, or platelet activating factor in a mouse model of orofacial pain.
The present study was carried out to determine the effects of central nervous free fatty acids, lysophospholipids, or platelet activating factor (PAF), in a mouse facial carrageenan injection model of orofacial pain. Mice that received intracerebroventricular (I. C. ⋯ C. V. lysophosphatidic acid or lysophosphatidylcholine injection, and at 8 and 24 h after PAF injection, compared vehicle injected controls. Information regarding pro-nociceptive effect of specific brain lipids may be a useful basis for further studies to explore mechanism.
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Comparative Study Clinical Trial
The "human visceral homunculus" to pain evoked in the oesophagus, stomach, duodenum and sigmoid colon.
The oesophagus, stomach, duodenum and sigmoid colon were electrically stimulated in 12 healthy volunteers with a thin nasal endoscope. The painful cortical evoked potentials (EPs) were recorded from 64 surface electrodes. The early EPs with latencies < 200 ms were studied and the corresponding dipole sources were calculated. ⋯ However, the position of the sources significantly changed depending on the stimulated gut tract. Moreover, while the SII and ACC sources were initially activated to oesophagus and stomach stimulation, the ACC and insular activities were the earliest ones after stimulation of the lower gut segments. The findings reflect differences in pathways and brain processing of visceral nociceptive inputs coming from either upper or lower gut and may improve our understanding of the brain-gut axis in health and disease.