Effects of bilateral inhibition of retrotrapezoid nucleus on breathing in conscious rats

Abstract

The last five years many studies suggested the retrotrapezoid nucleus (RTN) as the central respiratory chemoreceptors, however all experiments were performed in anesthetized animals. In the present study we sought to investigate a possible role of RTN neurons in the normal breathing in conscious rats. Male Holtzman rats (280–300 g) with bilateral stainless steel cannulas implanted into the RTN were used. In conscious rats, bilateral inhibition of RTN neurons with the GABA‐A agonist muscimol (100 pmol/50 nl) reduced resting ventilation (120±62, vs. saline: 928±77 ml/min/kg) and the increase in ventilation produced by hyperoxic hypercapnia (10% CO2) (962±174, vs. saline: 2654±231 ml/min/kg). However, muscimol into the RTN did not change the increase in ventilation produced by activation of peripheral chemoreceptors with hypoxia (8% O2) (1294±116, vs. saline: 1552±108 ml/min/kg). Bilateral injections of muscimol into the RTN slightly reduced resting MAP (Δ = −13±7, vs. saline: +3±2 mmHg), but did not affect the changes in MAP and HR produced by hyperoxia hypercapnia and peripheral chemoreceptor stimulation. In conclusion, RTN neurons activated by pCO2 presumably via their intrinsic chemosensitivity, provide chemical drive to breathe during resting or hypercapnia.Financial support: FAPESP and CNPq.