Premotor respiratory neurons from neonatal rats express a Ba(2+)-insensitive outward rectifying K+ channel (KOR) which is activated by gamma-aminobutyric acid acting at its beta receptor. The biophysical properties of KOR are similar to those described for the S-channel (KS) which underlies simple forms of non-associative learning in the marine mollusc Aplysia. We show here that KOR, like the S-channel, is inhibited by cAMP. In addition, we demonstrate that this inhibition is due to a change in closed time kinetics. Our data suggests that the ionic and biochemical substrates underlying synaptic plasticity in Aplysia have been phylogenetically conserved in mammalian motor circuits such as that controlling rhythmic breathing movements.