RESPIRATORY NEURONAL ACTIVITIES IN SPINAL AFFERENTS OF CAT

Abstract

1. In a series of intercollicular decerebrated cats, the spinal cord at the level of the second cervical segment was explored with a microelectrode in search for neuronal afferent discharges synchronous with the respiratory movement.2. Respiratory discharges could be encountered in the cuneate fascicle and in the portion corresponding to the dorsal spinocerebellar tract.3. Most of the respiratory discharges were found continuous without appreciable silent period, but the frequency of discharge varied in different phases of the cycle. Discharges were classified according to the phase of the cycle during which they occurred. Two types were found, inspiratory and expiratory. Each of them was again divided into three subgroups. Arranged in the order of frequent occurrence, the following types were obtained. A) Inspiratory discharge: i) the slow increment type in which activity builds up slowly and subsides abruptly, ii) the steady type in which constant level of high activity appears suddenly with inspiration, iii) the slow increment-decrement type in which activity builds up and subsides slowly. B) Expiratory discharge: i) the rapid increment type in which activity builds up suddenly and subsides slowly, ii) the steady type in which activity is periodically maintained at a constant high level, iii) the slow incrementdecrement type in which activity slowly builds up and subsides.4. Numerous units were found whose discharges were elicited only by passive distortion of the thorax. This type of discharges was considered to be of the same origin as the respiratory discharges.