Low-Frequency Neuromuscular Depression Is a Consequence of a Reduction in Nerve Terminal Ca2+ Currents at Mammalian Motor Nerve Endings.

Low-frequency Neuromuscular Depression Is a Consequence of a Reduction in Nerve Terminal Ca2+ Currents at Mammalian Motor Nerve Endings.

Anesthesiology. 2013 Mar 26;
Silinsky EM

BACKGROUND:: The decline in voluntary muscle contraction during low-frequency nerve stimulation is used clinically to assess the type and degree of neuromuscular block. The mechanism underlying this depression is unknown. METHODS:: Simultaneous electrophysiological measurements of neurotransmitter release and prejunctional Ca currents were made at mouse neuromuscular junctions to evaluate the hypothesis that decreases in nerve terminal Ca currents are responsible for low-frequency depression. RESULTS:: Under conditions generally used to measure Ca currents at the neuromuscular junction, increasing the frequency of nerve stimulation briefly from 0.017 to 0.1-1 Hz caused a simultaneous reduction in the release of the neurotransmitter acetylcholine to 52.2 ± 4.4% of control and the Ca current peak to 75.4 ± 2.0% of control (P < 0.001, n = 5 experiments for both measurements, mean ± SEM for all data). In conditions used for train-of-four monitoring (4 stimuli, 2 Hz), neurotransmitter release declined to 42.0 ± 1.0% of control and the Ca current peak declined to 75.8 ± 3.3% of control between the first and fourth stimulus (P < 0.001, n = 7 experiments for both measurements). Depression in acetylcholine release during train-of-four protocols also occurred in the absence of neuromuscular-blocking drugs. DISCUSSION:: The results demonstrate that neuromuscular depression during train-of-four monitoring is due to a decline in nerve terminal Ca currents, hence reducing the release of acetylcholine. As similar processes may come into play at higher stimulation frequencies, agents that antagonize the decline in Ca currents could be used to treat conditions in which neuromuscular depression can be debilitating. HubMed – depression


Preinjury Coping, Emotional Functioning, and Quality of Life Following Uncomplicated and Complicated Mild Traumatic Brain Injury.

J Head Trauma Rehabil. 2013 Mar 26;
Maestas KL, Sander AM, Clark AN, van Veldhoven LM, Struchen MA, Sherer M, Hannay HJ

OBJECTIVE:: To identify preinjury coping profiles among adults with uncomplicated mild traumatic brain injury (mTBI) and complicated mTBI and to determine whether preinjury coping profiles contribute to the prediction of emotional functioning and quality of life (QOL) 3 months post-mTBI. PARTICIPANTS:: One hundred eighty-seven persons with medically documented mTBI (uncomplicated mTBI, n = 89; complicated mTBI, n = 98) were recruited from the emergency center of a level I trauma center and followed in community 3 months post-mTBI. MEASURES:: The Ways of Coping Questionnaire was administered within 2 weeks of injury. Cluster analysis was used to group participants on basis of their preinjury use of problem-focused and avoidant coping strategies. The Brief Symptom Inventory and the 36-item Short-Form Health Survey were administered 3 months postinjury. RESULTS:: Cluster analysis distinguished 3 distinct preinjury coping profiles that were differentially associated with outcomes. Participants who used avoidant coping showed the worse emotional functioning and QOL outcomes, although this cluster also reported high usage of problem-focused strategies. Preinjury coping profiles explained a significant proportion of the variance in depression, anxiety, and mental health QOL at 3 months postinjury beyond that accounted for by demographic characteristics and mTBI severity. CONCLUSIONS:: Cluster analysis holds practical value in illustrating the pattern of coping strategies used by person with uncomplicated and complicated mTBI. It appears worthwhile to address coping in future trials of interventions that are aimed at improving emotional functioning after mTBI. HubMed – depression



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