Activation of neuronal ATP-sensitive potassium (KATP) channels is an important mechanism that protects neurons and conserves neural function during hypoxia. We investigated hypoxia (bath gassed with 95% N₂/5% CO₂ vs 95% O₂/5% CO₂ in control) induced changes in K_ATP current in second-order neurons of peripheral chemoreceptors in the nucleus of the solitary tract (NTS). Hypoxia-induced K_ATP currents were compared between normoxic rats (NORM), rats exposed to one week of either chronic sustained hypoxia (CSH) or chronic intermittent hypoxia (CIH). Whole-cell recordings of NTS second-order neurons identified following DiA labeling of the carotid bodies were obtained in a brainstem slice. In NORM cells (n=9), hypoxia (3 min) induced an outward current of 12.7±1.1 pA with a reversal potential of -73±2 mV. This current was completely blocked by the K_ATP channel blocker tolbutamide (100 µM). Bath application of the K_ATP channel opener diazoxide (200 µM, 3 min) evoked an outward current of 21.8±5.8 pA (n=6). Hypoxia elicited a significantly smaller outward current in both CSH (5.9±1.4 pA, n=11, p<0.01) and CIH (6.8±1.7 pA, n=6, p<0.05) neurons. Diazoxide elicited a significantly smaller outward current in CSH (3.9±1.0 pA, n=5, p<0.05) and CIH (2.9±0.9 pA, n=3, p<0.05) neurons. Western blot analysis showed reduced levels of K_ATP potassium channel subunits Kir6.1 and Kir6.2 in the NTS from CSH and CIH rats. These results suggest that hypoxia activates K_ATP channels in NTS neurons receiving monosynaptic chemoreceptor afferent inputs. Chronic exposure to either sustained or intermittent hypoxia reduces K_ATP channel function in NTS neurons. This may represent a neuronal adaptation that preserves neuronal excitability in crucial relay neurons in peripheral chemoreflex pathways.