Postsynaptic potentials of soleus motor neurons produced by transspinal stimulation: a human single-motor unit study.

Transspinal (or transcutaneous spinal cord) stimulation is a noninvasive, cost-effective, easily applied method with great potential as a therapeutic modality for recovering somatic and nonsomatic functions in upper motor neuron disorders. However, how transspinal stimulation affects motor neuron depolarization is poorly understood, limiting the development of effective transspinal stimulation protocols for rehabilitation. In this study, we characterized the responses of soleus α motor neurons to single-pulse transspinal stimulation using single-motor unit (SMU) discharges as a proxy given the 1:1 discharge activation between the motor neuron and the motor unit. Peristimulus time histogram, peristimulus frequencygram, and surface electromyography (sEMG) were used to characterize the postsynaptic potentials of soleus motor neurons. Transspinal stimulation produced short-latency excitatory postsynaptic potentials (EPSPs) followed by two distinct phases of inhibitory postsynaptic potentials (IPSPs) in most soleus motor neurons and only IPSPs in others. Transspinal stimulation generated double discharges at short interspike intervals in a few motor units. The short-latency EPSPs were likely mediated by muscle spindle group Ia and II afferents, and the IPSPs via excitation of group Ib afferents and recurrent collaterals of motor neurons leading to activation of diverse spinal inhibitory interneuronal circuits. Further studies are warranted to understand better how transspinal stimulation affects depolarization of α motor neurons over multiple spinal segments. This knowledge will be seminal for developing effective transspinal stimulation protocols in upper motor neuron lesions.NEW & NOTEWORTHY Transspinal stimulation produces distinct actions on soleus motor neurons: an early short-latency excitation followed by two inhibitions or only inhibition and doublets. These results show how transspinal stimulation affects depolarization of soleus α motor neurons in healthy humans.

Asymmetric dimethylarginine is not a good predictor of ischemia using myocardial perfusion scintigraphy.

BACKGROUND/AIM: Asymmetric dimethylarginine (ADMA) plays role in the pathogenesis of coronary artery disease and related mortality and morbidity through a number of mechanisms. We hypothesized that plasma ADMA levels would be increased in the presence of reversible ischemia as measured by GATED single photon emission computed tomography (SPECT) myocardial perfusion scintigraphy (MPS). MATERIALS AND METHODS: Fasting i.v. blood samples were drawn before testing. All patients underwent 99mTc-sestamibi GATED SPECT MPS with a one-day stress-rest protocol; the images were visually analyzed. Post-stress GATED parameters, including ejection fraction, end systolic and end diastolic volumes, and automatic stress defect scores, were recorded. RESULTS: The plasma ADMA levels were higher in the ischemic group than in the non-ischemic group (0.46 ± 0.19 vs. 0.40 ± 0.15; P = 0.016). Plasma ADMA levels (odds ratio [OR] = 13.5; 95% confidence interval [CI] = 1.7-109.01; P = 0.015) and sex (OR = 2.49, 95% CI = 1.18-5.26; P = 0.017) were independent predictors of ischemia. There was no linear correlation between plasma ADMA levels and both the GATED SPECT and stress test parameters. CONCLUSION: Our data support the hypothesis that increased baseline ADMA levels are independently related with the presence of reversible ischemia.