Morphology of the medullary chemosensitive fields. 1. Mapping of the neuronal matrix by a horseradish peroxidase technique.

A modified horseradish peroxidase labelling technique was used to study the distribution pattern of neurons in the central chemosensitive fields of the medulla oblongata of cats. In several cryosectioned medullae a mapping of superficially located HRP-labelled neurons was achieved. The distribution and configuration of the labelled neurons indicate that most of them belong to the nucleus paragigantocellularis lateralis. However, by varying the time of incubation it was possible to identify different types of neurons. On the basis of certain aspects of the HRP incorporation mode and neuronal topography a specific type of small-sized neurons has been identified. Some functional implications of these small neurons with respect to their possible chemosensitive activity are discussed.