Abstract
We have studied the fine anatomical architecture of the central respiratory chemoreceptor using electrophysiological, optical and histological techniques. We have identified medullary chemosensitive sites in the surface parts of the rostral ventrolateral medulla, raphe pallidus and parapyramidal regions. Pontine regions (locus coeruleus and A5 region) were also chemosensitive. We found two types of CO2-excitable cells (Type I and II cells) in the superficial ventral medulla. A Type I cell is smaller in size, located within the marginal glial layer, and intrinsically CO2-excitable. A cluster of Type I cells surround fine penetrating vessels, and a large surface vessel covers this region. A Type II cell is larger, located at a depth of a few hundred micrometer from the medullary surface, and excited transsynaptically by CO2. A single Type II cell forms dendro-somatic synapses with multiple Type I cells within the marginal glial layer, and sends axonal branches to multiple neurons of the ventral respiratory group (VRG). We propose a cell-vessel architecture model for the central respiratory chemoreceptor. Type I cells are primary chemosensors. In response to increased CO2 in perivascular tissue, Type I cells secrete neurotransmitter, and excite Type II cells. Excited Type II cells relay and amplify this information by innervating multiple VRG neurons. [J Physiol Sci. 2006;56 Suppl:S138]
