Laryngeal motoneurone activity in the rabbit during asphyxic gasping

Unitary activity was recorded from 44 recurrent laryngeal nerve (RLN) and 18 external laryngeal nerve (ELN) motoneurones in anaesthetized, paralysed rabbits during the development of periods of severe asphyxia caused by temporarily interrupting artificial ventilation. Ventilation was only recommenced when a simultaneously recorded phrenic neurogram showed the animal had attempted several gasps. Inspiratory-phased fibres (17 RLN, 14 ELN) displayed brief high frequency discharges with each gasp. Some inspiratory-phased ELN motoneurones (6/14) also displayed longer tonic discharges after each of the first few gasps. In the expiratory intervals immediately following each gasp many expiratory-phased fibres (13/21 RLN, 2/4 ELN) were active and 7 RLN fibres discharged a long train of impulses with a decrementing discharge pattern. In 3 anaesthetized rabbits, breathing spontaneously through a tracheostomy, a constant airflow was directed up through the larynx; successive gasps were associated with wide swings in translaryngeal pressure which were confirmed visually as reflecting rapid dilation of the glottis during gasps and intense constriction in the intervals between gasps.