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. 2012 Mar 6;112(10):1678–1688. doi: 10.1152/japplphysiol.00060.2012

Fig. 4.

Fig. 4.

Moderate, not severe, AIH-induced pLTF is significantly inhibited by 20 mM methysergide. A–C: representative traces of compressed, integrated phrenic neurograms during severe and moderate AIH compared with rats treated as time controls and not exposed to AIH after 20 mM methysergide spinal delivery (white, dashed line in each trace indicates baseline and black arrow indicates time of 20 mM methysergide delivery which was ∼10 min before the first hypoxic episode in each group). In A, enhanced pLTF (after severe AIH) is not altered in rats pretreated with spinal methysergide. In B, rats exposed to moderate AIH after spinal methysergide delivery exhibit abolished pLTF. In C, time control rats not exposed to AIH after spinal methysergide delivery do not exhibit time-dependent changes in phrenic motor output. D: phrenic burst amplitude (percentage change from baseline) in severe (n = 5; circles) and moderate AIH (n = 6; squares) protocols compared with rats treated as time controls (n = 5; triangles) and not exposed to AIH after 20 mM methysergide spinal delivery. pLTF is significantly increased by severe AIH after 20 mM methysergide delivery at 15, 30, 60, and 90 min posthypoxia compared with BL (†), at 15, 60 and 90 min posthypoxia compared with rats treated with moderate AIH (#) and at 60 and 90 min posthypoxia compared with rats treated as time controls (*) (all P < 0.05). Notice that phrenic amplitude in rats treated with moderate AIH after 20 mM methysergide is not significantly different from BL or from rats treated as time controls; thus moderate AIH induced pLTF is inhibited by 20 mM methysergide. E: phrenic frequency (percentage change from baseline) in severe (circles) and moderate AIH (squares) protocols compared with rats treated as time controls (triangles) and not exposed to AIH after 20 mM methysergide spinal delivery, where phrenic frequency was scaled the same as phrenic burst amplitude to enable direct comparisons of magnitude. Minimal LTF in phrenic nerve burst frequency is only seen with severe AIH at 60 min posthypoxia compared with BL (†), (P < 0.05).