Journal of neurophysiology
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1. The dynamic contribution of otolith signals to three-dimensional angular vestibuloocular reflex (VOR) was studied during off-vertical axis rotations in rhesus monkeys. In an attempt to separate response components to head velocity from those to head position relative to gravity during low-frequency sinusoidal oscillations, large oscillation amplitudes were chosen such that peak-to-peak head displacements exceeded 360 degrees. ⋯ Vectorial summation of canal VOR alone (elicited during earth-vertical axis rotations) and otolith VOR alone (elicited during off-vertical axis oscillations after semicircular canal inactivation) could not predict VOR gain and phase during off-vertical axis rotations in intact animals. This suggests a more complex interaction of semicircular canal and otolith signals. 7. The results of this study show that the primate low-frequency enhancement of VOR dynamics during off-vertical axis rotation is independent of a simultaneous activation of the vertical and torsional "tilt" otolith-ocular reflexes that have been characterized in the preceding paper. (ABSTRACT TRUNCATED)
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1. Recent studies have suggested that gamma-aminobutyric acid (GABA) inputs shape monaural and binaural neuronal response properties in the central nucleus of the inferior colliculus (CIC). CIC neurons receive major inhibitory GABAergic projections from intrinsic, commissural, and extrinsic sources. ⋯ These data suggest that GABA inhibition arises primarily from neurons with inhibitory fields aligned with their CIC targets. Thus the effect of the inhibition is primarily contained within or overlapping each target neuron's excitatory response area. CIC GABAergic circuits may function to adjust the gain needed for coding complex signals over a wide dynamic range.
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1. Thirty-three neurons in the L6-Sl spinal cord of 30 adult male Sprague-Dawley rats were characterized for responses to colorectal distention (CRD, 20-80 mmHg, 20 s) and convergent cutaneous receptive fields in the presence and absence of N-methyl-D-aspartate (NMDA; 1 microM) or D-serine (1 microM) administered locally by pressure ejection. 2. NMDA ejected locally increased the resting (spontaneous) activity, responses to CRD, postdistention afterdischarges, encoding of visceral nociception, and the size of convergent cutaneous receptive fields of some neurons. ⋯ The effects of D-serine were blocked by the glycine site antagonist 7-chloro-kynurenic acid (7-CK). 7-CK also blocked NMDA-produced effects on responses to CRD and increases in size of cutaneous receptive fields. 5. No differences were found between spinal neurons with and without documented long ascending projections with respect to effects of NMDA or D-serine. 6. These findings demonstrate involvement of spinal NMDA receptors in mediating hyperexcitability of spinal neurons to visceral nociceptive input and suggest an important contribution of spinal NMDA receptors in visceral hyperalgesic syndromes.
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1. The response of anterior parietal cortex to skin stimuli was evaluated with optical intrinsic signal imaging and extracellular microelectrode recording methods in anesthetized squirrel monkeys. 2. Nonnoxious mechanical stimulation (vibrotactile or skin tapping) of the contralateral radial interdigital pad was accompanied by a decrease in reflectance (at 833 nm) in sectors of cytoarchitectonic areas 3b and 1. ⋯ Spike discharge activity was recorded from area 3a neurons during a repetitive heating stimulus applied with a stationary probe/ thermode to the contralateral radial interdigital pad. Like the area 3a intrinsic signal elicited by repetitive heating of the same skin site, the area 3a neuron spike discharge activity also exhibited slow temporal summation and poststimulus response persistence. 7. The experimental findings suggest 1) a leading role for area 3a in the anterior parietal cortical processing of skin-heating stimuli, and 2) the presence of inhibitory interactions between the anterior parietal responses to painful and vibrotactile stimuli consistent with those demonstrated in recent cortical imaging and psychophysical studies of human subjects.
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1. A goal of this study was to determine whether neurons in the sacral spinal cord that project to the diencephalon are involved in the processing and transmission of sensory information that arises in the perineum and pelvis. Therefore, 58 neurons in segments L6-S2 were activated antidromically with currents < or = 30 microA from points in the contralateral diencephalon in rats that were anesthetized with urethan. 2. ⋯ As a population, WDR neurons, but not LT or HT neurons, encoded increasing pressures of CrD and VaD with graded increases in their firing frequencies. The responses of WDR neurons to CrD differed significantly from those of either LT or HT neurons. Regression analyses of the stimulus-response functions of responsive WDR neurons to CrD and VaD were described by power functions with exponents of 1.6 and 2.4, respectively.(ABSTRACT TRUNCATED)