Postnatal development of Na+-K+-2Cl− co-transporter 1 and K+-Cl− co-transporter 2 immunoreactivity in multiple brain stem respiratory nuclei of the rat

▶A critical period of postnatal respiratory development exists in rats around P12-P13. ▶NKCC1 expression decreases with age from P0 to P21, with marked reduction at P12. ▶KCC2 expression in seven brain stem respiratory nuclei increases with age from P0 to P21. ▶A distinct reversal of dominance from NKCC1 to KCC2 in the nuclei starts at P12. ▶The switch in NKCC1/KCC2 dominance potentiates inhibition during the critical period.