The developmental role of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) glutamate receptors in respiratory regulation remains undefined. To study this issue, minute ventilation (V˙E) was measured in 5-, 10-, and 15-day-old intact freely behaving rat pups using whole body plethysmography during room air (RA), hypercapnic (5% CO2), and hypoxic (10% O2) conditions, both before and after administration of the non- N-methyl-d-aspartate (NMDA) receptor antagonist 1,2,3,4-tetrahydro-6-nitro-2,3-dioxobenzo[f]quinoxaline-7-sulfonamide disodium (NBQX; 10 mg/kg ip). In all age groups,V˙E during RA was unaffected by NBQX, despite reductions in breathing frequency ( f) induced by increases in both inspiratory and expiratory duration. During hypoxia and hypercapnia, V˙Eincreases were similar in both NBQX and control conditions in all age groups. However, tidal volume was greater and f lower after NBQX. To determine if AMPA receptor-positive neurons are recruited during hypoxia, immunostaining for AMPA receptor (GluR2/3) and c -fos colabeling was performed in caudal brain stem sections after exposing rat pups at postnatal ages 2, 5, 10, and 20 days, and adult rats to room air or 10% O2 for 3 h. GluR2/3 expression increased with postnatal age in the nucleus of the solitary tract (NTS) and hypoglossal nucleus, whereas a biphasic pattern emerged for the nucleus ambiguus (NA). c -fos expression was enhanced by hypoxia at all postnatal ages in the NTS and NA and also demonstrated a clear maturational pattern. However, colocalization of GluR2/3 and c -fos was not affected by hypoxia. We conclude that AMPA glutamate receptor expression in the caudal brain stem is developmentally regulated. Furthermore, the role of non-NMDA receptors in respiratory control of conscious neonatal rats appears to be limited to modest, albeit significant, regulation of breathing pattern.