Birth-related expression of c-fos, c-jun and substance P mRNAs in the rat brainstem and pia mater: possible relationship to changes in central chemosensitivity

In situ hybridization was used to characterize respiration-related areas of the brainstem activated around the time of birth as well as their postnata l sensitivity to CO2. Levels of mRNA corresponding to the immediate early g enes (IEG), c-Sos and c-jun, and of substance P precursor, ppt-A, were dete rmined in rat fetuses (E21) and neonatal pups (1 h, 1 day and 6 days after normal birth) and after exposure to hypercapnia (12% CO2 for 1 h). Transien t increases in c-fos mRNA were observed in the central chemoreceptor area o f the ventral medullary surface (VMS), in the lateral reticular nucleus (LR N), in the nucleus of the solitary tract (NTS), and in the nucleus raphe pa llidus (RPA) 1 h after birth. Increased expression of c-fos mRNA in the VMS could also be evoked by hypercapnia and this response was particularly pro nounced I day after birth. On the other hand, c-jun mRNA could be detected already at E21 in the hypoglossal nucleus (XII) and LRN and these levels we re not significantly altered at 1 h after birth. There was, however, an inc rease in the expression of c-jun mRNA in the pia mater surrounding the brai nstem after birth. At I day after birth, c-jun mRNA levels had decreased in the LRN and pia mater, and later on (6 days after blah) in XII. Furthermor e, the ppt-A mRNA level in NTS increased immediately after birth and remain ed high 1 and 6 days later. These results suggest that (a) the central chem oreceptor area of the VMS, as well as the NTS, LRN, RPA and pia mater are a ctivated following birth; (b) the VMS, but not the other structures examine d, can be activated immediately after birth by hypercapnia; and (c) increas ed expression of ppt-A mRNA may be related to the transition of respiratory control at birth. (C) 1999 Elsevier Science B.V. All rights reserved.