The development and maturation of respiratory neuron and motoneuron discharge properties will be examined in two day to two month old swine.
Three specific aims will be pursued: (a) to determine age-related differences in numbers of inspiratory neurons with axons terminating in phrenic motoneuron pool and in responses to pulmonary afferent inputs; (b) to study age-related changes of neuronal responses to hypoxia and to identify neurons which could mediate hypoxic responses of phrenic motoneurons; (c) to compare efferent discharges of phrenic, recurrent laryngeal and hypoglossal motoneurons for differences in modulation by central pattern generators, responses to pulmonary afferent inputs, and responses during hypoxia. Experiments will be performed in Saffan anesthetized piglets; depth of anesthesia will be monitored by recording EEG, EKG and arterial blood pressure. Inspiratory neurons will be recorded extracellularly and responses to pulmonary afferent inputs will be determined using the No Inflation Test. In vagotomized piglets, neuronal responses to hypoxia will be classified according to changes in power spectra. For all neurons verification of single neuron recordings will be determined using interspike interval distributions, and the presence of excitatory connections with phrenic motoneurons will be determined using spike-triggered averaging. Modulation of nerve discharges by common central pattern generators will be evaluated using power and coherence spectral analyses. Age- dependent results will be determined by statistical comparisons of piglets at different ages. This research will provide new information regarding the development of medullary inspiratory neurons as well as phrenic, recurrent laryngeal and hypoglossal motoneurons. This information is clinically important since studies of neonatal breathing disturbances, i.e., SIDS, apnea, have implicated immaturities in responses to afferent inputs and in synaptic connections as etiological factors.
