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Departments of 1 Physiology and 2 Pediatrics, Perinatal Research Centre, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
The goal of this study was to determine when fetal breathing movements (FBMs) commence in the rat and to characterize age-dependent changes of FBMs in utero. These data provide a frame of reference for parallel in vitro studies of the cellular, synaptic, and network properties of the perinatal rat respiratory system. Ultrasound recordings were made from unanesthetized Sprague-Dawley rats from embryonic (E) day 15 (E15) to E20. Furthermore, the effects of respiratory stimulants (doxapram and aminophylline) and hypoxia on FBMs were studied. Single FBMs, occurring at a very low frequency (~8 FBMs/h), commenced at E16. The incidence of single FBMs increased to ~80 FBMs/h by E20. Episodes of clustered rhythmic FBMs were first observed at E18 (~40 FBMs/h). The incidence of episodic clustered FBMs increased to ~300 FMBs/h by E20, with the duration of each episode ranging from ~40 to 180 s. Doxapram, presumably acting to stimulate carotid body receptors, did not increase FBMs until E20, when the incidence of episodic clustered FBMs increased twofold. Aminophylline, a central-acting stimulant, caused an increase in episodic clustered FBMs after E17, reaching significance at E20 (3-fold increase). Exposing the dam to 10% O2 caused a rapid, marked suppression of FBMs (5-fold decrease) that was readily reversed on exposure to room air.
rhythmogenesis; diaphragm; phrenic motoneurons
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