Fig. 10.

Projections from retrotrapezoid nucleus (RTN) to parafacial respiratory group (pFRG) revealed by retrograde tracer. A: photomicrographies showing the typical injection site of the retrograde tracer cholera toxin subunit b (CTb) in the pFRG region. B–D: examples of neurons retrogradely labeled from the pFRG (CTb, B) and Phox2b-immunoreactivity (C) located in the RTN and colocalized (D). B′–D′: higher magnification of the region outlined in B–D. E: computer-generated plot of three injections of CTb that were confined to the pFRG, bregma level −11.36 to −11.12 mm, according to Paxinos and Watson (40). F: total number of RTN neurons (n = 3) detected in seven sections per brain (CTb and CTb + Phox2b neurons). Scales bar = 0.5 mm in A, 50 μm in D, 10 μm in D′, and 1 mm in E. 7, facial motor nucleus; py, pyramide; sp5, spinal trigeminal tract.