Developmental plasticity of phrenic motoneuron and diaphragm properties with the inception of inspiratory drive transmission in utero

The review outlines data consistent with the hypothesis that inspiratory drive transmission that generates fetal breathing movements (FBMs) is essential for the developmental plasticity of phrenic motoneurons (PMNs) and diaphragm musculature prior to birth. A systematic examination during the perinatal period demonstrated a very marked transformation of PMN and diaphragm properties coinciding with the onset and strengthening of inspiratory drive and FBMs in utero. This included studies of age-dependent changes of: i) morphology, neuronal coupling, passive and electrophysiological properties of PMNs; ii) rhythmic inspiratory activity in vitro; iii) FBMs generated in vivo detected by ultrasonography; iv) contractile and end-plate potential properties of diaphragm musculature. We also propose how the hypothesis can be further evaluated with studies of perinatal hypoglossal motoneuron-tongue musculature and the use of Dbx1 null mice that provide an experimental model lacking descending inspiratory drive transmission in utero.