Figure 1. Neurograms of representative LTF protocols showing integrated XII motor output in Young, Old and Old+T rats.

After establishing baseline conditions, three episodes of hypoxia (11–14%) were applied. Arterial blood samples for blood gas analysis (arrows) were taken under baseline conditions (BL), during the last minute of the first hypoxic episode (1.Hx) and at 15, 30 and 60 min after the last hypoxic episode (15′pHx, 30′pHx, 60′pHx). The upper panel shows a compressed tracing from a Young rat showing LTF typically seen in young male rats. The second panel shows the absence of LTF in an Old male rat. The third panel shows LTF in an Old male rat supplemented with testosterone (Old+T). The fourth panel shows the stability of end tidal CO₂ () throughout the protocol. The lower panel shows mean arterial blood pressure (MAP) throughout the protocol.