Phrenic (A) and XII (B) nerve burst amplitude at 15, 30, and 60 min post-mAIH in anesthetized Nx (n = 8) and rAIH (n = 9) rats. Results from time-control (TC) experiments in anesthetized Nx (n = 5) and rAIH (n = 15) rats that did not receive mAIH are also shown. Compared with TC groups, phrenic nerve burst amplitude was significantly elevated in Nx and rAIH rats at every time post-mAIH, demonstrating pLTF. Phrenic burst amplitude was significantly greater in rAIH than Nx rats (i.e., rats not pretreated with rAIH) at 60 min post-AIH, demonstrating pLTF metaplasticity. XII LTF was expressed in both treatment groups relative to baseline values, but not when compared at corresponding times in TC rats; one exception was significantly greater expression of XII LTF in rAIH rats at 60 min post-mAIH than in TC rats. There was no difference in XII nerve burst amplitude between rAIH and Nx rats at any time (i.e., rAIH did not enhance pLTF). Values are means ± SE. *Significantly different from baseline; @significantly different from Nx at corresponding time; #significantly different from corresponding TC within treatment group (P < 0.05).