Transcranial direct current stimulation influences the cardiac autonomic nervous control

To investigate whether the manipulation of brain excitability by transcranial direct current stimulation (tDCS) modulates the heart rate variability (HRV), the effect of tDCS applied at rest on the left temporal lobe in athletes (AG) and non-athletes (NAG) was evaluated. The HRV parameters (natural logarithms of LF, HF, and LF/HF) was assessed in 20 healthy men before, and immediately after tDCS and sham stimulation. After anodal tDCS in AG the parasympathetic activity (HF_log) increased (P < 0.01) and the sympathetic activity (LF_log) and sympatho-vagal balance (LF/HF_log) decreased (P < 0.01), whereas no significant effects were detected in NAG (P > 0.05). No significant changes in HRV indexes were provoked by sham stimulation in both AG and NAG (P > 0.05). In conclusion, tDCS applied on the left temporal lobe significantly increased the overall HRV in AG, enhancing the parasympathetic and decreasing the sympathetic modulation of heart rate. Consequently the sympatho-vagal balance decreased at rest in AG but not in NAG. Releasing a weak electric current to stimulate selected brain areas may induce favorable effects on the autonomic control to the heart in highly fit subjects.     

The effects of CO2 and pH on the spontaneous activity of the taenia coli of guinea-pig

Summary Mechanical and electrical activity of the isolated guinea-pig taenia coli were recorded in bicarbonate-, Tris- or phosphate-buffered test solutions. In normal solution (pCO₂ 5%, pH 7.4), typical minute-rhythmical fluctuations of activity occurred, whereby activity was present for approximately 40% of the total time (active time), the other 60% being activity-free intervals. At constant extracellular pH, low CO₂ content increased active time, high CO₂ content reduced it. Extracellular alkalinization at constantpCO₂ also diminished active time, even in CO₂-free medium, whereas acidification raised it, sometimes causing continuous activity. At constant bicarbonate-buffer, changes of CO₂ content, i.e. accompanied by corresponding changes in pH, affected the active time much less than did CO₂ alterations in an isohydric medium. The test solutions had no major effect on frequency of synchronized spike discharges, in contrast to their actions on the minuterhythmical activity. Since CO₂ can pass through the cell membrane more easily than ions regulating intra- and extracellular pH, the observed effects are best explained by changes in the transmembrane pH-gradient. A drop in active time would be due to a relative intracellular acidification; continuous activity, on the other hand, due to an opposite change in transmembrane pH-gradient, i.e. a relative intracellular alkalinization.This work was supported by the Deutsche Forschungsgemeinschaft