Journal of neurophysiology
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Current-clamp recordings with the use of the whole cell configuration of the patch-clamp technique were made from postnatal mouse spiral ganglion neurons in vitro. Cultures contained neurons that displayed monopolar, bipolar, and pseudomonopolar morphologies. Additionally, a class of neurons having exceptionally large somata was observed. ⋯ Inward rectification was evaluated in response to hyperpolarizing contrast current injections. Present in both electrophysiological classes, its magnitude was graded from neuron to neuron, reflecting differences in number, type, and/or voltage dependence of the underlying channels. These data suggest that spiral ganglion neurons possess intrinsic firing properties that regulate action potential number and timing, features that may be crucial to signal coding in the auditory periphery.
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The segmental organization of the hindlimb locomotor pattern generators and the coordination of rhythmic motor activity were studied in isolated spinal cords of the neonatal rat. All lumbar segments and many thoracic and sacral segments of the cord exhibited an alternating left-right rhythm in the presence of serotonin (5-HT) and N-methyl-D-aspartate (NDMA). Other thoracic segments exhibited a synchronized left-right rhythm or an irregular bursting activity. ⋯ Local application of strychnine to L2 kept bilaterally intact in midsagittally split preparations perturbed but did not completely block the alternating pattern of the rhythm induced by 5-HT and NMDA. Local application of bicuculline under the same conditions prolonged the cycle time and had no effect on left-right alternation. These results, together with those described above, suggest that left-right alternation is mediated mainly by strychnine-sensitive glycine receptors with possible contribution of strychnine-resistant glycine receptors and/or GABAA receptors.
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Clinical Trial
Motor task difficulty and brain activity: investigation of goal-directed reciprocal aiming using positron emission tomography.
Differences in the kinematics and pattern of relative regional cerebral blood flow (rCBF) during goal-directed arm aiming were investigated with the use of a Fitts continuous aiming paradigm with three difficulty conditions (index of difficulty, ID) and two aiming types (transport vs. targeting) in six healthy right-handed young participants with the use of video-based movement trajectory analysis and positron emission tomography. Movement time and kinematic characteristics were analyzed together with the magnitude of cerebral blood flow to identify areas of brain activity proportionate to task and movement variables. Significant differences in rCBF between task conditions were determined by analysis of variance with planned comparisons of means with the use of group mean weighted linear contrasts. ⋯ Differences in unimanual aiming task difficulty lead to dissociable activation of cortical-subcortical networks. Further, these data suggest that when more precise targeting is required, independent of task difficulty, a cortical-subcortical loop composed of the contralateral motor cortex, intraparietal sulcus, and caudate is activated. This is consistent with the role of motor cortex
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In our previous study, pairing-induced transient synaptic potentiation in supragranular layers of the visual cortex was described in mature guinea pigs. In the present study, the development of this type of synaptic plasticity and the underlying cellular mechanisms that mediate it were evaluated in animals from postnatal day (PND) 5 to 180. Potentiation is more reliably evoked in younger animals (likelihood: 75%, PND 5-30; 51%, PND > or = 34), and the magnitude of the effect is greater (+40 +/- 3%, mean +/- SE, PND 5-30; +26 +/- 3%, PND > or = 34). ⋯ Synaptic potentiation was prevented (8 of 11 cases) or was replaced by synaptic depression (3 of 11 cells) in experiments in which postsynaptic calcium levels were reduced by intracellular application of 1,2-bis-2-aminophenoxy ethane-N,N,N',N'-tetraacetic acid (BAPTA) in the cortex of young (PND 7-14) animals, or in which the extracellular calcium concentrations was lowered. Inhibition of postsynaptic calcium-induced calcium release blocked synaptic potentiation (4 of 4 cells). Prolonged superfusion (3 h) of the nitric oxide synthase inhibitor L-nitro-arginine (LNA) did not significantly affect the likelihood (in LNA, 81%; 13 of 16 cells), or the magnitude (+38 +/- 7% increase in LNA vs. +40 +/- 3% in control cases) of potentiation, in contrast to its effects in the mature cortex.
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In mammals with good low-frequency hearing and a moderate to large interear distance, neurons in the medial superior olive (MSO) are sensitive to interaural time differences (ITDs). Most small mammals, however, do not hear low frequencies and do not experience significant ITDs, suggesting that their MSOs participate in functions other than ITD coding. In one bat species, the mustached bat, the MSO is a functionally monaural nucleus, acting as a low-pass filter for the rate of sinusoidally amplitude-modulated (SAM) stimuli. ⋯ The different time constants of inputs create a low-pass filter for SAM stimuli. However, the MSO output is an integrated response to the temporal structure of a stimulus as well as its azimuthal position, i.e., IIDs. There are no in vivo results concerning filter characteristics in a "classical" MSO, but our data confirm an earlier speculation about this interdependence based on data accessed from a gerbil brain slice preparation.