Differential expression of respiratory long-term facilitation among inbred rat strains

We tested the hypotheses that: (1) long-term facilitation (LTF) following acute intermittent hypoxia (AIH) varies among three inbred rat strains: Fischer 344 (F344), Brown Norway (BN) and Lewis rats and (2) ventral cervical spinal levels of genes important for phrenic LTF (pLTF) vary in association with pLTF magnitude. Lewis and F344, but not BN rats exhibited significant increases in phrenic and hypoglossal burst amplitude 60 min post-AIH that were significantly greater than control experiments without AIH, indicating strain differences in phrenic (98%, 56% and 20%, respectively) and hypoglossal LTF (66%, 77% and 5%, respectively). Ventral spinal 5-HT2A receptor mRNA and protein levels were higher in F344 and Lewis versus BN, suggesting that higher 5-HT2A receptor levels are associated with greater pLTF. More complex relationships were found for 5-HT7, BDNF and TrkB mRNA. BN had higher 5-HT7 and TrkB mRNA versus F344; BN and Lewis had higher BDNF mRNA levels versus F344. Genetic variations in serotonergic function may underlie strain differences in AIH-induced pLTF.