Figure 6
Modulation of nerve activity mediated by changes in nerve temperature. (A) Diagram of preparation for heating or cooling the nerve with a Peltier device. Nerve temperature was monitored with a thermocouple. Recording electrodes on the nerve are shown. (B) Examples of CAPs at different temperatures relative to baseline CAPs (baseline refers to ES of foot with no US applied). (C) Change in VRMS of CAPs is plotted as a function of changes in nerve temperature, revealing a negative correlation. Data from one animal. (D) Diagram of preparation for heat dissipation experiments. The cold side of Peltier device was put under the nerve as a cooler to dissipate heat induced by US stimulation of the nerve. Shown in the lower protocol diagram, baseline corresponds to the change in VRMS from two consecutive E-Only sessions. US-mod corresponds to change in VRMS between EU-paired session with its preceding E-only session when the cooler was off. US-mod with cooler paradigm corresponds to when the Peltier cooler was on. (E) Examples of changes of nerve temperature and nerve activity in one animal. When turning on the cooler (US-mod with cooler), the nerve temperature did not continue to increase as occurs during US stimulation (left plot, red versus blue curves), and suppression of nerve activity was not observed (middle plot). Statistical analysis over three sessions showed that the cooler successfully prevented suppression of nerve activity (right plot). * indicates p = 0.02. (F-G) Three diverse US parameters were tested on three animals. Examples of averaged CAPs and temperature changes for different paradigms are plotted in F. US (1.6 MPa, 10 ms PD; 0.5 MPa, 100 ms PD; 0.3 MPa, 500 ms PD) suppressed nerve activity by 11.68 ± 7.77%, 19.06 ± 4.87%, and 24.44 ± 4.74%, respectively. With the cooler, the nerve activity could be enhanced above baseline activity (16.91% ± 12.82% for 1.6 MPa, 10 ms PD) or to baseline activity (0.5 MPa, 100 ms PD and 0.3 MPa, 500 ms). The 0.22 MHz transducer was used in these thermal experiments. Data are represented as mean ± SD.
