The perinatal ontogeny of preprotachykinin-A gene expression was assessed in central respiration-related structures. On the day of birth, there was an enhanced expression of preprotachykinin-A mRNA in the region of the nucleus tractus solitarii, the primary relay station for respiratory and cardiovascular reflexes. This increased expression was also seen in the pups delivered by cesarean section and allowed to breathe for a couple of hours as compared with their littermates, which were not allowed to breathe at all. On the basis of this finding, we suggest that the commencement of continuous breathing at birth, unlike the episodic breathing of fetal life, is associated with the enhanced expression of preprotachykinin-A mRNA in the nucleus tractus solitarii.