Julius H. Comroe, Jr., distinguished lecture: central chemoreception: then ... and now

Abstract

The 2010 Julius H. Comroe, Jr., Lecture of the American Physiological Society focuses on evolving ideas in chemoreception for CO₂/pH in terms of what is "sensed," where it is sensed, and how the sensed information is used physiologically. Chemoreception is viewed as involving neurons (and glia) at many sites within the hindbrain, including, but not limited to, the retrotrapezoid nucleus, the medullary raphe, the locus ceruleus, the nucleus tractus solitarius, the lateral hypothalamus (orexin neurons), and the caudal ventrolateral medulla. Central chemoreception also has an important nonadditive interaction with afferent information arising at the carotid body. While ventilation has been viewed as the primary output variable, it appears that airway resistance, arousal, and blood pressure can also be significantly affected. Emphasis is placed on the importance of data derived from studies performed in the absence of anesthesia.

Fig. 1.

A simplified, schematic view of chemoreceptor sites that, when stimulated, can increase ventilation in wakefulness. Red areas represent chemosensitive sites identified via focal acidification in vivo or via effects of focal, specific neuronal inhibition. Red-green areas identify chemosensitive sites that also express a Phox2b background. Solid lines identify connections known to be present in wakefulness. In non-rapid eye movement sleep, orexinergic neurons of the lateral hypothalamus (Li, Li and Nattie; unpublished data) and retrotrapezoid nucleus (RTN) neurons may participate less (61), while serotonergic neurons may participate more (75). LH, lateral hypothalamus; LC, locus ceruleus; NTS, nucleus tractus solitarius; CB, carotid body; PBC, pre-Bötzinger complex; rVRG, rostral ventral respiratory group; MR, medullary raphe; VLM, ventrolateral medulla.