Advances in Neural Signal Processing and Modeling: Dynamics of the Respiratory Neural Networks during Maturation

Abstract

Previous studies in various animal models have shown that respiratory premotor and motor neurons undergo rapid changes in biochemical and bioelectric properties during the first month of postnatal life. Early in postnatal life, there is an increase in the complexity of the morphology of the dendritic tree of respiratory neurons as it changes from a bipolar to a multipolar morphology. During normal breathing (eupnea), the phrenic nerve has a slow, ramping output which reflects the orderly recruitment of phrenic motoneurons throughout inspiration when viewed in the time domain. Hypercapnia stimulates the respiratory system increasing both the respiratory frequency and amplitude. During severe hypoxia, the output of the phrenic nerve initially increases then, with prolonged hypoxia, falls to zero. Phrenic activity returns with a completely different firing pattern, gasping. During gasping the phrenic nerve fires with an abrupt onset and rises rapidly to maximal neural activity with a decrementing decline. During recovery from hypoxia, a variety of respiratory patterns between eupnea and gasping are seen in the time domain.

These observations suggest that hypoxia reduces the phrenic neurogram activity and reverses the configuration of respiratory neural network. However, very limited data are available on the dynamics (complexity) of the activities of medullary respiratory neurons during eupnea, gasping and recovery from hypoxia in vivo. Therefore, the effect of hypoxia and hypercapnia on the dynamics (complexity) of medullary respiratory neurons and the respiratory output, the phrenic neurogram is not yet fully understood.

The aim of this talk is a) to characterize and quantify the complexity of activities of the rostral ventrolateral medullary neurons including the “pre-Botzinger” complex to gain insights into how respiration is generated during unstimulatd breathing in eupnea, and during hypoxia and hypercapnia during early maturation, and b) to determine the influence of selective and complete inhibition of respiratory neurons in the rostral ventrolateral medulla on the dynamics of respiratory pattern in perfusate rats.