Effects of postnatal development, temperature and the pons on respiratory rhythm and pattern generation in rat pups

Episodic breathing is common in premature infants and is found in fetal rats but rarely reported in postnatal (P) in vitro preparations. We discovered that episodic breathing patterns were common (>60%) in in vitro pontomedullary-spinal cord preparations at 27°C from rat pups on the day of birth (P0), but the occurrence of this breathing pattern declined with postnatal development. Chemical inhibition and physical removal of the pons eliminated the episodic breathing pattern at P0. Interestingly, episodic breathing patterns could be restored in older preparations (P2 – P4) by decreasing temperature (23°C), with or without the pons. In preparations held at 27°C, with a continuous rhythm, an episodic rhythm could be produced by activating GABA receptors (100μM GABA). In preparations with an episodic pattern, antagonism of opioid receptors by naloxone (1–5μm) did not affect the episodic rhythm while blockade of GABAA receptors by bicuculline (BIC, 10μM) converted the episodic rhythm to a continuous rhythm. However, in preparations held at 23°C, BIC (10μM) had the opposite effect, promoting episodicity. Together, these data suggest the mechanisms required for episodic rhythm generation are intrinsic to the medulla, and are modulated by postnatal development, temperature sensitive mechanisms (such as TRP channels) and pontine factors. Funded by NSERC (Canada).