Journal of neurophysiology
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1. Using positron emission tomography and measurement of regional cerebral blood flow (rCBF) as an index of cerebral activity we investigated the central processing of motor preparation in 13 healthy volunteers. 2. We used a motor reaction time paradigm with visual cues as preparatory and response signals. ⋯ Thus the parietal cortex may play a more crucial role than the secondary motor areas in integrating visual information in preparation for movement. 7. The effect on brain activity of the internal (self-generated) versus the external (cued) mode of movement selection was assessed by comparing the free and full conditions, the preparatory component being matched in the two conditions. The anterior part of the supplementary motor area was the main area preferentially involved in the internal selection of movement, independently of motor preparation processes.
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1. The purpose of this study is to define the cortical regions that subserve voluntary saccadic eye movements and spatial working memory in humans. 2. Regional cerebral blood flow (rCBF) during performance of oculomotor tasks was measured with [15O]-H2O positron emission tomography (PET). ⋯ During the antisaccade task, the ventral region of lower rCBF involved medial structures including left ventral striatum and bilateral medial temporal-limbic cortex. During the ODR task, the ventral aspect of the region of lower rCBF extended laterally, rather than medially, to include the temporal poles. The lower blood flow observed in ventromedial PFC during both the antisaccade and ODR tasks, relative to the visually guided saccade and fixation tasks, suggests that modulation of output from ventromedial PFC to limbic cortex and the striatum may play a role in the voluntary control of saccadic eye movements, possibly in the suppression of responses that would interrupt
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1. gamma-Aminobutyric acid (GABA) is thought to inhibit both pre- and postsynaptically the transfer of nociceptive signals from primary afferent fibers to spinal dorsal horn sensory cells, including spinothalamic tract (STT) neurons. The inhibition can be mediated by both GABAA and GABAB receptors. We now attempt to characterize the synaptic inhibition of STT cells by spinal GABAA and GABAB receptors in anesthetized monkeys and to analyze the roles of these two receptor subtypes in the inhibition of STT cellular activity produced by stimulation in the periaqueductal gray (PAG). 2. ⋯ A possible presynaptic GABAA action was not investigated. Our finding of a GABAB-receptor-mediated inhibition is consistent with the view that both pre- and postsynaptic GABAB receptors are involved in inhibitory modulation of spinal nociceptive transmission. Finally, it is suggested from this study that primate spinal GABAA, but not GABAB receptors, are involved in mediating the descending inhibition induced by PAG stimulation.
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1. The electrophysiological properties of rat corticospinal neurons (CSNs) were studied 3, 9, and 12 mo after axotomy in the cervical spinal cord, with the use of a combination of the in vitro neocortical slice technique, intracellular recordings, and a double-labeling method that allowed identification of CSNs studied in vitro. 2. CSNs retained the rhodamine-labeled microspheres employed as a retrograde marker and were functionally active in the longest survival group (1 yr). 3. ⋯ The proportions of neurons generating IPSPs were significantly smaller than in comparable groups of control CSNs. As a consequence, longer duration evoked excitatory postsynaptic potentials were generated by axotomized CSNs. 8. Results show that axotomized CSNs undergo alterations in intrinsic membrane properties and inhibitory synaptic electrogenesis that would tend to make them more responsive to excitatory inputs.
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1. The effect of the calcium channel antagonist diltiazem on pH-induced sustained nociceptor excitation was investigated in a rat skin-saphenous nerve preparation, in vitro, where receptive fields of identified and isolated single fibers were superfused at the corium side with controlled solutions to assess their chemosensitivity. 2. Unmyelinated mechano-heat sensitive ("polymodal") C fiber terminals (n = 78) were superfused with a CO2-saturated synthetic interstitial fluid (CO2-SIF, pH 6.1). ⋯ Superfusion for 6 min of diltiazem 10(-5) M was sufficient to block axonal conduction as well as mechanosensitivity, which both recovered synchronously during wash out. 8. It can be concluded from the results that the suppressive effect of diltiazem on pH-induced nociceptor excitation can be explained by a use-dependent axonal block, comparable with the action of local anesthetics and affecting all modalities of sensory responsiveness. 9. The findings provide no indication that a transformed calcium channel specifically sensitive to diltiazem is involved in pH-induced sustained nociceptor excitation.