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We assessed ventilatory patterns and ventilatory responses to hypoxia (HVR) in high-altitude (HA) plateau pikas, repetitively exposed to hypoxic burrows, and control rats. We evaluated the role of neuronal nitric oxide synthase (nNOS) and dopamine by using S-methyl-L-thiocitrulline (SMTC) inhibitor and haloperidol antagonist, respectively. Ventilation ([V.sub.I]) was measured using a whole body plethysmograph in conscious pikas (n = 9) and low-altitude (LA) rats (n = 7) at different [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (56, 80, 111,150, and 186 mmHg) and in HA acclimatized rats (n = 9, 8 days at 4,600 m) at two different [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (56 and 80 mmHg). The effects of NaCl, SMTC, and haloperidol on ventilatory patterns were assessed in pikas at [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] = 56 and 80 mmHg. We observed a main species effect with larger [V.sub.I], tidal volume (VT), inspiratory time/total time ([T.sub.i]/[T.sub.tot]), and a lower expiratory time in pikas than in LA rats. Pikas had also a larger VT and lower respiratory frequency compared with HA rats in hypoxia. HVR of pikas and rats were not statistically different. In pikas, SMTC induced a significant increase in [V.sub.I] and VT for a [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] of 56 mmHg, but had no effect for a [P.sub.I][O.sub.2] of 80 mmHg, i.e., the living altitude of pikas. In pikas, haloperidol injection had no effect on any ventilatory parameter. Long-term ventilatory adaptation in pikas is mainly due to an improvement in respiratory pattern (VT and [T.sub.i]/[T.sub.tot]) with no significant improvement in HVR. The sensitivity to severe acute hypoxia in pikas seems to be regulated by a peripheral nNOS mechanism. adaptation; control of breathing; dopamine doi: 10.1152/ajpregu.00108.2009.