BLOCKADE OF SYNAPTIC INHIBITION WITHIN THE PRE-BOTZINGER COMPLEX IN THE CAT SUPPRESSES RESPIRATORY RHYTHM GENERATION IN-VIVO

1. The role of synaptic inhibition in respiratory rhythm generation wa s analysed by microinjections of GABA(A) and glycine receptor antagoni sts into the bilateral pre-Botzinger complex (PBC) of anaesthetized ca ts. Central respiratory activity was monitored by phrenic nerve record ings. 2. Bilateral injections of bicuculline (50 or 100 mu M) irrevers ibly slowed respiratory frequency and induced apneustic patterns. 3. B ilateral injections of strychnine (50 or 100 mu M) greatly reduced phr enic burst amplitudes leading to increased burst frequency or irrevers ibly blocked rhythmic phrenic discharges. After unilateral tetrodotoxi n (TTX) blockade in the PBC, strychnine injection into the contralater al PBC blocked rhythmic phrenic discharges. 4. Bilateral blockade of b oth G-ABAergic and glycinergic inhibition abolished rhythmic burst dis charges and only tonic phrenic activity remained. Such tonic activity was blocked only by TTX (1 mu M). 6. Potentiation of synaptic inhibiti on by the serotonin 1A receptor agonist 8-hydroxydipropylaminotetralin (8-OH-DPAT; 50 mu M) restored rhythmic activity only when given short ly after strychnine and bicuculline applications. It was, however, ine ffective after blockade of synaptic inhibition was complete. 7. The st udy demonstrates the significance of synaptic inhibition in the proces s of respiratory generation in the adult cat in vivo.