REAPPRAISAL OF THE INSPIRATORY EFFECT OF BOTZINGER COMPLEX ON PHRENIC-NERVE DISCHARGE

Experiments were done on 12 urethane-chloralose anaesthetized, vagotom ized, paralysed and ventilated cats. The effects of electrical microst imulation at the augmenting expiratory neurons (Aug-e) of Botzinger co mplex (Bot.c) were investigated. It was found that long train stimulat ion (100 Hz, 3-50 mu A, 4-6 s) caused intensity-dependent inhibition o f phrenic inspiratory discharge. The threshold for complete inhibition was 10 +/- 2 mu A (mean +/- S.E.). The expiratory duration showed sho rtening at low intensity (<7 mu A) and prolongation at higher intensit y. Short train stimulation (10 mu A, 50 ms) delivered in inspiratory p hase produced a two-part transient inhibition of phrenic discharge. Th e latencies of the first- and second-part inhibition were 4.7 +/- 0.16 ms and 95 +/- 3 ms, respectively. Complete termination of inspiration could be produced by a short train delivered at late inspiration. The results suggest the importance of the Aug-e neurons of Bot.c in deter mining inspiratory amplitude and respiratory phase duration.