Respiratory-Related Evoked Potential Measure of Intrinsic Transient Tracheal Occlusion Elicited Cortical Activations in Rats

Author(s): Pei-Ying S Chan, Shin-Yi Tsao, Hsiu-Wen Tsai, Hsin-Yung Chen, Kuan-Yi Wu, Paul W. Davenport

Respiratory-related evoked potentials (RREP) measured with inspiratory mechanical stimulation have been demonstrated in humans and lambs. Previous studies have shown that the source of the RREP early P1 peak was generated by activation of neurons in the somatosensory (S1) cortex in humans. The RREP in rodents with mechanical loads induced by tracheal occlusions has never been studied before. Therefore, a rat intrinsic transient tracheal occlusion (ITTO) model was developed to test this hypothesis. The electrocorticogram (ECoG) was recorded in 8 chronically instrumented, awake and spontaneously breathing male Sprague-Dawley rats. On the day of recording, the animal was placed into a minimally restrictive restraint apparatus. The ECoG was recorded for 2.5 minutes as control prior to the occlusions. During the occlusion protocol of 10 to 18 minutes (collecting at least 70 occlusions), the occlusions lasted for 3 to 5 breaths and were presented approximately every 30 seconds. Occlusion-elicited evoked potentials were obtained by computer-signal averaging the ECoG activity triggered by the onset of inspiration. Two peaks (peak 1 and peak 2) were observed in the averaged occlusionelicited evoked potentials in all animals. Latencies and amplitudes were identified for each peak in every animal, and each peak was compared among day 1, 3, 5, 7, and 10 using the one-way repeated measures of ANOVA. The short-latency peak 1 showed a trend of increased amplitude at day 3 compared to day 1 (0.52 ± 0.14 V, and 0.23 ± 0.03 V, respectively, p < 0.1), whereas the longer latency peak 2 showed an increase in amplitude at day 3 compared to day 1 (-0.31 ± 0.094 V, and -0.14 ± 0.16 V, respectively; p < 0.05). Besides, peak 2 showed a longer latency on day 10 compared to day 1 in 5 animals. The result demonstrated that the ITTO protocol was feasible to elicit an evoked potential in the S1 cortex in awake, spontaneously breathing rats. The change in peak amplitude and latency may suggest cortical neural changes in respiratory sensory information processing with a chronic load conditioning program. Future studies are in need to further confirm these findings and to investigate the interactions between psychological and physiological factors in respiratory sensation.

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