The hypoxic respiratory response in mammals consists of a transit increase in the respiratory frequency (augmentation phase) followed by a decrease in frequency (depression phase). To understand how the central respiratory system contributes to this response, the in vitro transverse brainstem slice model is used, which contains the pre-Bötzinger Complex, which is responsible for respiratory rhythm generation. The in vitro experiments performed for this thesis provide evidence that external barium exposure alters respiratory activity and significantly increases (P<0.00 1) the voltage of tonic activity under control oxygen conditions (95% FO2). During severe hypoxia (0% FO2), respiratory tonic activity is significantly elevatedduring the depression phase (from 0.55 to 0.95, n=6, P<0.001) by external barium, presumablydue to the closing of K+ channels and a reduction in K+ conductance.