PO2 of the metathoracic ganglion in response to progressive hypoxia in an insect

Mammals regulate their brain tissue PO2 tightly, and only small changes in brain PO2 are required to elicit compensatory ventilation. However, unlike the flow-through cardiovascular system of vertebrates, insect tissues exchange gases through blind-ended tracheoles that may involve a more prominent role for diffusive gas exchange. We tested the effect of progressive hypoxia on ventilation and the PO2 of the metathoracic ganglion (neural site of control of ventilation) using micro-electrodes in the American locust, Schistocerca americana. In normal air (21 kPa), PO2 of the metathoracic ganglion was 12 kPa. The PO2 of the ganglion dropped as air PO2 dropped, with ventilatory responses occurring when ganglion PO2 reached 3 kPa. Unlike vertebrates, insects tolerate relatively high resting tissue PO2 levels, and allow tissue PO2 to drop during hypoxia, activity and discontinuous gas exchange before activating convective or spiracular gas exchange. Tracheated animals, and possibly pancrustace...