Developmental Origin of PreBotzinger Complex Respiratory Neurons

A subset of preBotzinger Complex (preBotC) neurokinin 1 receptor (NK1R) and somatostatin peptide (SST)-expressing neurons are necessary for breathing in adult rats, in vivo. Their developmental origins and relationship to other preBotC glutamatergic neurons are unknown. Here we show, in mice, that the "core" of preBotC SST+/NK1R(+)/SST 2a receptor(+) (SST2aR) neurons, are derived from Dbx1-expressing progenitors. We also show that Dbx1-derived neurons heterogeneously coexpress NK1R and SST2aR within and beyond the borders of preBotC. More striking, we find that nearly all non-catecholaminergic glutamatergic neurons of the ventrolateral medulla (VLM) are also Dbx1 derived. preBotC SST+ neurons are born between E9.5 and E11.5 in the same proportion as non-SST-expressing neurons. Additionally, preBotC Dbx1 neurons are respiratory modulated and show an early inspiratory phase of firing in rhythmically active slice preparations. Loss of Dbx1 eliminates all glutamatergic neurons from the respiratory VLM including preBotC NK1R(+)/SST+ neurons. Dbx1 mutant mice do not express any spontaneous respiratory behaviors in vivo. Moreover, they do not generate rhythmic inspiratory activity in isolated en bloc preparations even after acidic or serotonergic stimulation. These data indicate that preBotC core neurons represent a subset of a larger, more heterogeneous population of VLM Dbx1-derived neurons. These data indicate that Dbx1-derived neurons are essential for the expression and, we hypothesize, are responsible for the generation of respiratory behavior both in vitro and in vivo.