2.5 |. Thoracic SNA and PNA in response to acute NaCl overload in in situ preparations of rats with removal of carotid bodies

The juvenile rats (n = 5) were submitted to removal of the carotid bodies (CBX) using a modification of the technique described by Abdala et al. (2012). Briefly, 24 h before the in situ experiments, rats were anaesthetized with halothane (2% in O₂) and fixed in a supine position. Using strict aseptic techniques, an anterior midline incision (3 cm) was made in the neck to expose the muscles that cover the trachea and carotid bifurcation region. The sternohyoid and sternocleidomastoid muscles were carefully retracted, the carotid bifurcation was exposed, the occipital artery was retracted, and the carotid body was visualized and removed. The procedures were performed bilaterally. Subsequently, the midline neck incision was sutured using silk for surgical closure of the wounds, and both groups (sham and CBX) received anti-inflammatory ketoprofen [1%,0.03 ml (100 g)⁻¹, S.C.] and were monitored until they regained consciousness.

One day after the surgical procedures, rats were prepared for in situ recordings of tSNA and PNA. The chemoreflex and baroreflex responses were tested with intra-arterial infusion of potassium cyanide (KCN; 25 μg in 50 μl; Sigma-Aldrich, St Louis, MO, USA) and phenylephrine (10 μg in 100 μl; α₁-adrenergic agonist; Sigma-Aldrich), respectively. The surgery of carotid body removal was considered effective when the tachypnoea and sympathoexcitation induced by the stimulation of the peripheral chemoreceptors with KCN, but not baroreflex-induced sympathoinhibition (increase of 25–40 mmHg in the perfusion pressure), were abolished. After these tests, the in situ preparations of CBX rats received intra-arterial infusions of Ringer solution followed by hyperosmotic NaCl (0.17, 0.3, 0.7, 1.5 and 2.0 mol l⁻¹), as described above.