Conditional expression of central respiratory rhythm in developing fat‐tailed dunnarts (Marsupialia: Sminthopsis crassicaudata)

Abstract

Marsupials offer unparalleled opportunities for developmental studies as the young are born small and immature, with most development occurring in the pouch where the young are readily accessible. The fat‐tailed dunnart gives birth to one of the smallest newborns of any mammal (~4mm long, weighing 13‐15mg). Newborn dunnarts do not typically breathe until 3‐4 days postnatal (P), achieving gas exchange largely across the skin (Mortola et al., Nature, 1999). Currently, little is known about the development of respiratory rhythmogenesis in this species. We examined central respiratory rhythm in neonatal dunnarts from the day of birth up to 3 weeks of age (206‐261mg) using the in vitro brainstem‐spinal cord preparation. Under normocapnic conditions (5% CO2/95% O2, pH 7.4), fictive breathing was present at P0 and frequency increased with development until about P12. In P0 preparations, under normocapnia, fictive respiratory bursts occurred in episodes but became regular with increased drive (8% CO2, pH 7.2). In P5 and older preparations, under normocapnia, breathing was regular and fictive respiratory frequency correlated with the level of drive at all ages. These data indicate that dunnarts on the day of birth are capable of generating central respiratory rhythm even though expression of the rhythm does not occur for several days. (Supported by NSERC of Canada).