pLTF in 28d treated rats. A and B, Representative traces of compressed, integrated phrenic nerve activity before and after AIH in 28d CTB-SAP rats pre-treated with keto veh (A) or keto (B). Baseline is indicated in each trace by a white, dashed line. AIH elicits an enhanced pLTF in 28d CTB-SAP rats pre-treated with keto, while pLTF appears to be more moderate with keto veh pre-treatment. C, D. Phrenic burst amplitude (expressed as a percent change from baseline) in 28d control (C) and 28d CTB-SAP (D) rats pre-treated with keto veh, keto veh TC, keto, or keto TC. pLTF was significantly increased from baseline (*) at 30 and 60 min in 28d control rats pre-treated with keto veh and keto, and 60 min in 28d CTB-SAP rats with the same pre-treatments. pLTF was significantly greater than respective time controls at 30 and 60 min in 28d control rats pre-treated with keto veh, and at 60 min in 28d control and CTB-SAP rats pre-treated with keto and 28d CTB-SAP rats pre-treated with keto veh (†). 28d CTB-SAP rats pre-treated with keto had a significantly greater pLTF than that of 28d CTB-SAP rats pre-treated with keto veh (#). Values are expressed as means ±1 S.E.M, and differences were considered significant if p < 0.05.