Journal of neurophysiology
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Action potentials and voltage-gated currents were studied in acutely dissociated neurosecretory cells from the rat supraoptic nucleus during the first three postnatal weeks (PW1-PW3), a period corresponding to the final establishment of neuroendocrine relationships. Action potential duration (at half maximum) decreased from 2.7 to 1.8 ms; this was attributable to a decrease in decay time. Application of cadmium (250 microM) reduced the decay time by 43% at PW1 and 21% at PW3, indicating that the contribution of calcium currents to action potentials decreased during postnatal development. ⋯ A similar reduction was obtained when only the density of the potassium current was increased. Integration of the calcium currents generated during mature and immature action potentials demonstrated a significant decrease in calcium entry during development. We conclude that the developmental reduction of the action potential duration 1) is a consequence of the developmentally regulated increase in a sustained potassium current and 2) leads to a reduction of the participation of calcium currents in the action potential, resulting in a decreased amount of calcium entering the cell during each action potential.
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Clinical Trial
Saccades to remembered targets: the effects of smooth pursuit and illusory stimulus motion.
1. Measurements were made in four normal human subjects of the accuracy of saccades to remembered locations of targets that were flashed on a 20 x 30 deg random dot display that was either stationary or moving horizontally and sinusoidally at +/-9 deg at 0.3 Hz. During the interval between the target flash and the memory-guided saccade, the "memory period" (1.4 s), subjects either fixated a stationary spot or pursued a spot moving vertically sinusoidally at +/-9 deg at 0.3 Hz. 2. ⋯ We tested the possibilities that the brain made an accurate memory of target location and a reliable representation of the eye movement during the memory period, or that one or both of these was corrupted by the illusory visual stimulus. Our data were best accounted for by a model in which both the working memory of target location and the internal representation of the horizontal eye movements were corrupted by the illusory visual stimulus. We conclude that extraretinal signals played only a minor role, in comparison with visual estimates of the direction of gaze, in planning eye movements to remembered targ
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Comparative Study Clinical Trial
Response compatibility and the relationship between event-related potentials and the timing of a motor response.
1. Earlier studies have shown that changes in the difficulty of sensory discrimination in a choice reaction time task result in a prolongation of the peak latency for several components of the long-latency event-related potential (ERP). With the use of the technique of response-locked averaging, we have previously shown that manipulation of the difficulty of sensory discrimination also affects response execution as assessed by the interval between the ERP and onset of the response. ⋯ However, despite the similarly tight coupling of the response to the ERP in both the compatible and noncompatible conditions, the response occurred later relative to the ERPs in the noncompatible condition. This suggests that different components of the ERP are responsible for triggering the response in different circumstances. Our observations on the error trials suggests that the decision to respond (on these trials) is based on the occurrence of cerebral events that are evoked by either rare or frequent stimuli, whereas this decision (on correct response trials) is based on cerebral events elicited only by the rare stimuli.
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1. In early local feedback models for controlling horizontal saccade amplitude, a feedback signal of instantaneous eye position is continuously subtracted from a reference signal of desired eye position at a comparator. The output of the comparator is dynamic motor error, the remaining distance the eyes must rotate to reach the saccadic goal. ⋯ Moreover, the peak velocity-amplitude relationships, the instantaneous velocity profiles, and the ratio of horizontal and vertical velocities and durations were very similar to those of visually guided saccades. 7. Independent comparator models can readily account for the ability to manipulate the amplitude of one component of oblique saccades without affecting the other. However, two-dimensional local feedback models that cannot exert independent control over the horizontal and vertical amplitudes of oblique saccades should be carefully reevaluated.
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Comparative Study
Presynaptic A1 inhibitory/A2A facilitatory adenosine receptor activation balance depends on motor nerve stimulation paradigm at the rat hemidiaphragm.
1. Adenosine modulates acetylcholine (ACh) release from the rat motor nerve terminals. Tonic activation of presynaptic A1 inhibitory and/or A2A facilitatory adenosine receptors is regulated by the concentration of the nucleoside at the synapse. ⋯ In contrast, the inhibitory effect of the A1 receptor agonist R-N6-phenylisopropyladenosine was significantly attenuated in both stimulation conditions. 6. In conclusion, the results suggest that high-intensity, high-frequency motor nerve stimulation critically influences endogenous adenosine formation and the A1/A2A receptor activation balance, i.e., it potentiates the tonic adenosine A2A-receptor-mediated facilitation of ACh release, whereas activation of the inhibitory A1 receptors becomes less effective. A model is proposed that attempts to further elucidate adenosine's involvement in synaptic transmission adaptation.