Inhibition of the commissural nucleus of the solitary tract inhibits peripheral but not central chemoreflex in rats

A large variety of sensory afferents converges to the nucleus of the solitary tract (NTS) and influences the activity of ventrolateral medullary (VLM) neurons involved in cardiovascular and respiratory regulations. Here, we investigated the effects of inhibition of the commissural NTS (commNTS) on cardiovascular and respiratory responses to chemoreflex activation in conscious and anesthetized male Holtzman rats (280‐300g, n = 7/group). In conscious rats, electrolytic lesions of the commNTS eliminated the increase in mean arterial pressure (MAP) (Δ= +8±4, vs. sham: +45±18 mmHg) and reduced the increase in ventilation (404±43, vs. sham: 773±28 ml/min/kg) produced by activation of peripheral chemoreflex with KCN (40 μg/rat) intravenously (iv). However, electrolytic lesion of the commNTS did not change the increase in ventilation produced by activation of central chemoreceptors with increased levels of CO 2 (7%) (1189±32, vs. sham: 1055±53 ml/min/kg). In urethane anesthetized animals, the injection of the GABA‐A agonist muscimol (2 mM ‐ 60 nL) into the commNTS eliminated the increase in MAP (Δ= +6±3, vs. saline: +23±18 mmHg), on phrenic nerve discharge (PND) and on splanchnic sympathetic nerve discharge (sSND). Muscimol into the commNTS did not change the activation of central chemoreceptors with CO 2 (7%) on PND and sSND. In conclusion, the integrity of commNTS is important for the cardiorespiratory responses elicited by peripheral but not central chemoreflex activation.