Journal of neurophysiology
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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.
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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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Dorsal root ganglion neurons from adult rats (> or = 200 g) were maintained in culture for between 1 and 3 days. Membrane currents generated by large neurons (50-75 microns apparent diameter) were recorded with the whole cell patch-clamp technique. Large neurons generated transient Na+ currents and at least two types of inward current that persisted throughout 200-ms voltage-clamp steps to +20 mV. ⋯ We conclude that the low-threshold current is a TTX-sensitive, persistent Na+ current. The persistent TTX-sensitive current contributed to steady-state membrane current from at least -70 mV to 0 mV, a wider potential range than predicted by activation-inactivation gating overlap for transient Na+ current. Because of its low threshold and fast activation kinetics, the persistent Na+ current is expected to play an important role in determining membrane excitability.
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Single-neuron activity was recorded in the prefrontal cortex of three monkeys during the performance of a spatial delayed alternation (DA) task and during the presentation of a variety of visual, auditory, and somatosensory stimuli. The aim was to study the relationship between mnemonic neuronal processing and other functional neuronal responsiveness at the single-neuron level in the prefrontal cortex. Recordings were performed in both experimental situations from 152 neurons. ⋯ This study provides further evidence about the significance of the dorsolateral prefrontal cortex in spatial working memory processing. Although a considerable number of all DA task-related neurons responded to visual, somatosensory, and auditory stimulation or to the movements of the monkey, most delay-related neurons engaged in the spatial DA task did not respond to extrinsic sensory stimulation. These results indicate that most prefrontal neurons firing selectively during the delay phase of the DA task are highly specialized and process only task-related information.