6533b82dfe1ef96bd129144e

RESEARCH PRODUCT

The bulbar respiratory centre in the rabbit. I. Changes of respiratory parameters caused by intermittent electrical bulbar stimulation during inspiration or expiration.

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In anesthetized rabbits, spirogram and diaphragmatic activity were examined during electrical stimulation of the bulbar lateral reticular formation. The activity of bulbar respiratory neurons was recorded contra-or ipsilaterally to the stimulation site. One volley of repetitive stimuli per breath was delivered during either inspiration or expiration. 1. Each volley of about 120 ms duration at 100 pulses per second, delivered early ininspiration, caused an immediate and transient inhibition of the diaphragmatic activity. An inspiratory, rebound comprising lengthening of inspiration and increase in tidal volume occurred. a) “Inspiratory” and “expiratory-inspiratory” phase-spanning neurons exhibited inhibition during the volley. The burst discharge was lengthened and the spike density increased after the stimulus. The same was true of some “inspiratory-expiratory” phasespanning units. b) The discharge of most of the “inspiratory-expiratory” neurons was not inhibited. “Expiratory” units were excited. In both types of cells activation occurred which outlasted the volley. 2. When applied duringexpiration, the volley caused a short inspiratory twitch. a) “Inspiratory” and “expiratory-inspiratory” neurons exhibited a short post-stimulus firing and the spike density was increased. In some units of the latter type, however, the burst discharge was shortened. b) Most of the “expiratory” and “inspiratory-expiratory” neurons were not inhibited by the volley. Cells of the former type often produced post-stimulus after-discharge; the burst discharge of units belonging to the latter type was shortened. The effects of expiratory stimuli upon neuronal activity, however, were less consistent than those elicited by inspiratory volleys. 3. During spontaneous irregularities of single inspirations (short interruptions), EI and I neurons exhibited comparable burst pattern changes. The changes in pattern of IE and E units were also comparable and differed distinctly from the behaviour of the EI and I cells. No major differences in behaviour were observed between neurons which were inhibited during lung inflation (α units) and those which were activated during inflation (β cells). The findings are in accord with the effects observed during electrical bulbar stimulation, suggesting that EI and I units are inspiratory-activating cells, whereas IE and E neurons may have an inspiratory-inhibitory function. 4. The conclusion is drawn that the effects of bulbar stimulation on the respiratory movements are the result of manipulation on intrinsic rhythmogenesis.