Episodic breathing patterns in neonatal rats: neurochemical modulation, developmental changes and pontine influences

Abstract

Episodic breathing is prevalent in premature infants and is found in fetal rats but rarely reported in postnatal (PN) in vitro preparations. We observed episodic breathing patterns in the in vitro pontomedullary‐spinal cord preparation from rat pups on day of birth (P0) and PN day 2 (P2), but the occurrence declined with PN age with 70% of P0 and 20% of P2 preparations exhibited episodic patterns. In P0 preparations, episodic inspiratory bursting was recorded from cervical rootlets (C4/C1), hypoglossal and thoracic nerves (T1/T2), and episodic expiratory bursts coupled to inspiratory bursts were recorded from the 12th thoracic nerve rootlet. As neonates are highly sensitive to respiratory depression by opioids, we hypothesized that endogenous opioids participate in the production of the apneas between the episodes. Activation of opioid receptors (DAMGO 1–2μM) increased apnea duration but antagonism with naloxone (1–5μM) did not alter apnea duration or the episodic pattern, suggesting that endogenous opioids do not mediate the episodic rhythm. We also examined the role of the pons in the generation of the episodic rhythm. Both chemical inhibition and physical removal of the pons eliminated the episodic breathing pattern. Our data suggests that the pons is involved in the generation of episodic rhythms but that this involvement decreases and is lost over the first two PN days.