Impacts of strain, age, and temperature on respiratory pattern and rhythm<i>in vivo</i>in the neonatal rat

Variability in breathing rhythm and pattern are hallmarks of the early neonatal period in mammals. Despite this being well described in the literature, occurring both in in-vitro nerve recordings from reduced preparations as well as in the whole animal, there is little data documenting how this variability changes and stabilizes into a regular respiratory rhythm over the early neonatal period. It is also not clear how external factors such as species and temperature play a role in the degree of variability. Using impedance electrodes, we measured breathing pattern and frequency in two strains of neonatal rat pups (Sprague Dawley and Long Evans) exposed to two different temperatures (33 and 27C) on postnatal days 0, 1, 2, and 4. Age strongly influenced breathing frequency, with a significant increase in frequency and decrease in both short and long-term variability between P0 and P1 in both strains. Temperature did not have a significant effect on frequency or variability across age groups or between strains. This sudden change in frequency and variability may be due to a rapid shift in populations of inhibitory neurotransmitters within the respiratory pacemaker network in the brainstem. Further neurophysiological experiments will aid in identifying the key neurotransmitters responsible for mediating this shift and further our understanding of the broader significance of this rapid transition during early mammalian development. Funded by the NSERC of Canada.s This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.