Phox2b, RTN/pFRG neurons and respiratory rhythmogenesis.

Phox2b-expressing cells in the parafacial region of the ventral medulla are proposed to play a role in central chemoreception and postnatal survival. Recent findings in the adult rat and neonatal mouse suggest that the Phox2b-immunoreactive (ir) cell cluster in the rostral ventrolateral medulla is composed of glutamatergic neurons and expresses neurokinin 1 receptor (NK1R), indicating that the cluster may be identical to the retrotrapezoid nucleus. This region overlaps at least partly with the parafacial respiratory group (pFRG) composed predominantly of pre-inspiratory (Pre-I) neurons that are involved in respiratory rhythm generation. Recently, we showed that Pre-I neurons in the parafacial region (pFRG/Pre-I) in neonatal rats are indeed expressing Phox2b and are postsynaptically CO(2) sensitive. Our findings suggest that Phox2b-expressing pFRG/Pre-I neurons play a role in respiratory rhythm generation as well as central chemoreception and thus are essential for postnatal survival. In this brief review, we focused on these recent findings and discuss the functional role of pFRG/Pre-I neurons.