Expression of hypoglossal long-term facilitation differs between substrains of Sprague-Dawley rat

Long-term facilitation (LTF) is a prolonged, serotonin-dependent augmentati on of respiratory motor output following episodic hypoxia. Previous observa tions lead us to hypothesize that LTF is subject to genetic influences and, as a result, differs between Sprague-Dawley (SD) rats from two vendors, Ha rlan (H) and Charles River Laboratories/Sasco (CRL/S). Using a blinded expe rimental design, we recorded integrated phrenic (integral Phr) and hypoglos sal neurograms in anesthetized, vagotomized, paralyzed, and ventilated rats . At 60 min following three 5-min hypoxic episodes (Pa-O2 = 40 +/- 1 Torr; 5-min hyperoxic intervals), integral Phr was elevated from baseline in both SD substrains (i.e., LTF; P < 0.05). Conversely, hypoglossal LTF was prese nt in CRL/S but not H rats (P, 0.05 between substrains). Serotonin immunore activity within the hypoglossal nucleus was not different between H and CRL /S rats. We conclude that the expression of hypoglossal LTF differs between SD rat substrains, indicating a difference in their genetic predisposition to neural plasticity.