Bilateral [D-Ala,² N-MePhe,⁴ Gly-ol]-enkephalin (DAMGO) injection into the “tachypneic area” of the parabrachial nucleus (tPBN) significantly reduced respiratory rate and drive in young and adult rabbits, which was reversible with local naloxone. (A) Phrenic neurogram (PNG; a.u. [arbitrary units]) tracing during control and after drug injections in an individual adult rabbit. (B) Summary data for changes in respiratory rate. (C) Summary data for changes in other respiratory parameters. Gray bars: young (n = 14). White bars: adult (n = 11). Data show mean ± SD. *P < 0.05, **P < 0.01, and ***P < 0.001 indicate significant differences between drug application conditions (linear mixed model with factors: drug application and developmental age). There were no differences in drug effects between young and adult animals.