<Originals>Changes in unit activities of VPL thalamic neurons after middle cerebral artery occlusion in rats
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概要
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Evoked responses in VPL thalamic neurons following infarction of the somatosensory cortex were examined in anesthetized rats. The cortical infarction was produced by middle cerebral artery occlusion (MCAO). One, 4 and 7 days after MCAO, VPL neuron activities evoked by electrical stimulation of the contralateral forelimb were recorded with 2M-NaCl-filled glass microelectrodes. The electrical stimulus was applied 25 times. The frequency of repetition was gradually increased from 1 to 50 Hz. At each frequency the average number of spikes in response to each group of 25 stimuli (firing probability) was calculated. The infarcted area and the degenerative changes in the thalamus were evaluated after staining with 2,3,5-triphenyltetrazolium chloride (TTC). The evoked unit activities could be detected at all times studied. Firing probability of the VPL units decreased with increased stimulation frequency. In the control group, the reduction in the firing probability was mild, while in the MCAO groups the reduction became more prominent especially 1 day after MCAO. One day after MCAO all the units were less responsive to somatosensory inputs, and by the fourth day after MCAO the responsiveness of several neurons had recovered to levels close to those of the control preparations. In the TTC staining study, reduction of stainability was observed in the ipsilateral thalamus 4 days after MCAO. The present study demonstrates the existence of functional neurons even 7 days after MCAO, and shows that somatosensory cortical and/or subcortical infarction depresses somatosensory transmission in VPL neurons.
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