The activity of late inspiratory cells during the behavioral inhibition of inspiration.

Cats can be trained to stop inspiration behaviorally--a response mediated by inactivation of brainstem inspiratory neurons. Neurons that discharge late in the inspiratory phase of the respiratory cycle may terminate that phase; therefore, such cells may be activated behaviorally to inhibit inspiration. To test this hypothesis, we studied the activity of late-onset inspiratory neurons located in the dorsal and ventral medullary respiratory groups in cats trained to stop inspiration behaviorally. Twenty-eight of 112 respiratory neurons were classified as late-onset inspiratory neurons. They had an average eta 2 value of 0.58 (+/- 0.13, S.D.) and an average maximal discharge rate of 42 Hz (+/- 18, S.D.). For most cells, the period of activity varied under different conditions: some extended their activity into early inspiration; others, into early expiration. Eighteen of these late-onset inspiratory neurons were completely silent when the animals stopped inspiration behaviorally, and 10 discharged only a few action potentials. The latter response was weak and inconsistent, and we conclude that late inspiratory cells do not inhibit other brainstem inspiratory cells when animals stop inspiration behaviorally.