Abstract
The infrared (IR) inhibition of axonal activities in the crayfish neuromuscular preparation is studied using 2 µm IR light pulses with varying durations. The intracellular neuronal activities are monitored with two-electrode current clamp, while the IR-induced temperature changes are measured by the open patch technique simultaneously. It is demonstrated that the IR pulses can reversibly shape or block locally initiated action potentials. Suppression of the AP amplitude and duration and decrease in axonal excitability by IR pulses are quantitatively analyzed. While the AP amplitude and duration decrease similarly during IR illumination, it is discovered that the recovery of the AP duration after the IR pulses is slower than that of the AP amplitude. An IR-induced decrease in the input resistance (8.8%) is detected and discussed together with the temperature dependent changes in channel kinetics as contributing factors for the inhibition reported here.
Highlights
Modulation of neural and muscular activity is essential for both basic research and clinical applications
The average temperature increase induced by such one IR pulse was estimated as 8.7± 0.26 °C (N = 5, see Fig. 1(b))
As the IR light induced local temperature increase is not insignificant (8–12 °C), we believe that temperature dependent changes in Na+ and K+ channel kinetics may play a significant role in the IR induced inhibition and AP waveform modulation
Summary
Modulation of neural and muscular activity is essential for both basic research and clinical applications. Potential advantages of infrared stimulation over electric stimulation include high spatiotemporal precision, noninvasiveness and contact-free delivery [5,8]. The underlying biophysical mechanisms and the intricate interplay of various contributing factors to infrared nerve interactions remain an interesting research field. Changes in the membrane capacitance caused by spatiotemporal temperature gradients have been demonstrated to depolarize cells and elicit action potentials [10,11,12,13]. Other postulated mechanisms associated with IR stimulation include the activation of temperature sensitive ion channels [17], the formation of nanopores in the plasma membrane [18], and optoacoustic effects resulting from nanosecond laser pulse stimulation [19,20]. Depending on the stimulation parameters, the cell physiology and the structure of the biological systems studied, different biophysical mechanisms have been shown to be dominant
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