Development of respiratory pattern in mice (1177.1)

Maturation of mouse respiratory pattern in vivo has been studied (Euro J Neurosci 17:1233, 2003). The results, however, were grouped at P0‐P2. In vitro recordings from en block late embryonic rat brainstem spinal cord preparation showed prolonged neuronal activity in cervical ventral root 5 bursts (J Neurophysiol 67:996, 1992). Here we show in C57BL6/J mice a change in respiratory pattern from P0.5 to P2. Studies were performed with body plethysmography at ~32°C. This system (J Appl Physiol 56:1533, 1984) determines inspiratory and expiratory flow. At P0.5 (wt=1.38±0.08g) TI showed a sustained plateau pattern lasting 253±17 ms. TE (173±14 ms) was shorter resulting in a duty cycle (TI/TTOT) of 0.59±0.01. Respiratory frequency increased from 145±9 bpm at P0.5 to 188±19 at P2 (wt=1.73±.05g). The increase in frequency was entirely due to a change in TI that decreased from 253±17 to 135±11 ms. Inspiratory flow no longer showed a plateau during most breaths. TE remained constant over the first 2 postnatal days (173±14 vs 208±22 ms). TI/TTOT was reduced from 0.59±0.01 to 0.40±0.01. The results suggest that pontine pneumotactic centre and/or its afferent inputs are no fully mature in P0.5 mice. Grant Funding Source : Supported by Rett Syndrome Research Trust