Chronic intermittent hypoxia (CIH) in rats produces changes in central regulation of cardiovascular and respiratory systems by unknown mechanisms. We hypothesized that CIH (6% O2 for 40 s, every 9 min, 8 h/day) for 10 days alters the central respiratory modulation of sympathetic activity. After CIH, awake rats (n=14) exhibited higher levels of mean arterial pressure than controls (101±3 vs 89±3 mmHg, n=15, P<0.01). Recordings of phrenic, thoracic sympathetic (tSNA), cervical vagus (cVN) and abdominal nerves (Abd) were performed in the in situ working heart-brainstem preparations of control and CIH juvenile rats. The data obtained in CIH rats revealed that: (i) Abd nerve exhibited an additional burst discharge in late expiration; (ii) tSNA was greater during late expiration than in controls (52±5 vs 40±3%; n=11, P<0.05; values expressed according to the maximal activity observed during inspiration and the noise level recorded at the end of each experiment), which was not dependent on peripheral chemoreceptors; (iii) the additional late expiratory activity in the Abd nerve correlated with the increased tSNA; (iv) the enhanced late expiratory activity in the Abd nerve unique to CIH rats was accompanied with reduced post-inspiratory activity in cVN compared to controls. The data indicate that CIH rats present an altered pattern of central sympathetic-respiratory coupling, with increased tSNA that correlates with enhanced late expiratory discharge in the Abd nerve. Thus, CIH alters the coupling between the central respiratory generator and sympathetic networks that may contribute to the induced hypertension on this experimental model.