GABA receptors in the phrenic nucleus of the rat

The phrenic nucleus was identified by microinjections of N-methyl-D-asparti c acid in urethan-anesthetized adult male Wistar rats. Microinjections of G ABA(A) and GABA(B) receptor agonists (muscimol and baclofen, respectively) at the same site decreased the phrenic nerve burst amplitude. Microinjectio ns of GABA(A) and GABA(B) receptor antagonists(bicuculline and 2-hydroxysac lofen, respectively) blocked as well as reversed the effects of their respe ctive agonists. These results were confirmed by recording extracellular act ion potentials from single phrenic neurons. Micropressure applications of m uscimol and baclofen decreased the activity of single neurons in the phreni c nucleus; this effect was blocked as well as reversed by micropressure app lications of bicuculline and 2-hydroxysaclofen, respectively. Those results demonstrated the presence of GABA receptors on the neurons in the phrenic nucleus and suggested that their activation results in the decrease of the phrenic nerve burst amplitude. The importance of these results in the ident ification of neural circuits mediating inhibition of phrenic neurons is dis cussed.