Passive limb movement augments ventilatory response to CO2 via sciatic inputs in anesthetized rats

Passive limb movement (PLM) in humans induces a phasic hyperpnea, but the underlying physiological mechanisms remain unclear. We asked whether PLM in anesthetized rats would produce a similar phasic hyperpnea associated with an augmented ventilatory (V˙E) response to CO2 that is dependent on sciatic afferents. The animals underwent 5 min threshold PLM, 3 min hypercapnia (5% CO2), and their combination (CO2 exposure at the end of 2nd min of 5-min PLM) before and after bilateral transection of the sciatic nerves. We found that a threshold PLM evoked a phasic hyperpnea, similar to that denoted in humans, and an augmented V˙E response to CO2. Both responses were greatly diminished by sciatic nerve transection. Moreover, similar responses were also evoked by electrically stimulating the central end of the transected sciatic nerve. Our findings suggest an ability of the sciatic afferents to augment the V˙E response to CO2 that likely contributes to the PLM-induced hyperpnea.