A review of functional and structural components of the respiratory center involved in the arousal response.

State-dependent changes influencing both the central chemoreceptor and vagal inputs to respiratory neurons may provide useful markers to assess some intrinsic factors of the respiratory center. In this paper we discuss the following topics from our recent experiences, and their relevance to the assessment of sleep-related phenomena. (1) 'Post-sigh' apnea appears predominantly during non-REM sleep in control subjects, and is a potential marker of respiratory dysfunction during this stage of sleep. (2) The disarranged configuration of the arcuate nucleus in Fukuyama-type congenital muscular dystrophy may represent a disturbance in the tangential migration pathway in the brainstem, and may be related to the sudden death that is common in this disorder. The maldevelopment of the arcuate nucleus in the victims of sudden infant death syndrome (SIDS) may also be related to some abnormality in the differentiation and migration of this neuronal population. (3) The onset of hypoglossal nerve activity precedes inspiratory activity of the phrenic nerve, possibly representing a latent drive from the respiratory rhythm generator. These issues are not only related to respiratory rhythmogenesis itself, but are also important in understanding the pathological conditions of arousal responses.