| Summary: | 碩士 === 國立中山大學 === 生物科學系研究所 === 102 === High cervical spinal cord injury usually changes the respiratory pattern, which may influence the pulmonary vagal afferent activity. Previous study revealed that pulmonary chemoreflex cannot be evoked following acute C2 hemisection (C2Hx). The first aim of this study is to examine whether capsaicin-induced chemoreflex can recover following chronic C2Hx. Adult male Sprague-Dawley rats received sham operation (i.e., control group) or C2Hx. Pulmonary chemoreflex were evoked by intra-jugular administration of capsaicin in 2 or 8 weeks post-surgery rats. Results showed that pulmonary chemoreflex can be evoked; however, the apneic period in complete C2Hx group was weaker than control group. Linear regression analysis of complete and incomplete C2Hx rats indicated that respiratory pattern and pulmonary chemoreflex recovered as the severity of spinal cord injury decreased. The second aim of the present study was to investigate whether background activity of lung C-fibers can influence the breathing pattern during the chronic injury phase by blocking lung C-fiber conduction using perivagal capsaicin treatment. Our data showed pulmonary chemoreflex was attenuated by perivagal capsaicin treatment; however the respiratory pattern was not changed after perivagal capsaicin treatment in control and complete C2Hx rats. We conclude that capsaicin-induced apnea was attenuated following chronic C2Hx; moreover, it recovers as the severity of spinal cord injury decrease. Nevertheless, respiratory pattern remains unchanged after blocking lung C-fibers. Recovery of pulmonary chemoreflex reveals that the occurrence of inflammation may decrease because the defensive reflex altered in the chronic phase.
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