Ventilatory effects accompanying spontaneous movement in the suckling opossum

To determine whether spontaneous movement was associated with an organized respiratory response during early stages of mammalian development, we studied immature suckling opossums (Didelphis virginiana) between 30 and 60 days of age. Rate and depth of breathing were measured using pressure plethysmography and movement was assessed using electromyography of neck muscles. During air-breathing as well as during ventilatory chemostimulation with hypoxic, hypercapnic, and asphyxiant test gases, the onset of spontaneous movement was often marked by an increase in minute-ventilation, dominated by an increase in breathing frequency. In the absence of respiratory irregularities, ventilation and breathing frequency remained elevated throughout an episode of movement. After decerebration at the midcollicular level, the onset of spontaneous movement was accompanied by respiratory effects similar to those found in the intact preparation. The ventilation response with spontaneous movement contrasted to results during venilatory chemostimulation at rest, where increases in breathing resulted primarily from increases in tidal volume. It is concluded that a hyperpnea with spontaneous movement is present in the suckling opossum, and that the effect is primarily organized in the lower brainstem.