Anatomical organization of cat intercostal motor nuclei as demonstrated by HRP retrograde labelling.

1. Intercostal muscles participate both in postural and respiratory functions to a variable degree dependent upon the specific interspace or muscle. In order to determine if these physiological properties are related to a special organization at the spinal cord level, we have used the retrograde transport of HRP as a tool for studying the spinal distribution and morphology of intercostal motor cells in the adult cat. 2. Results obtained after intramuscular injections of the enzyme suggest that the intercostal motor columns could be distributed, in thoracic spinal segments, among two areas according to the respiratory or postural muscle specialization. Moreover, it appears that both postural and respiratory muscles are innervated by motor cells whose size is not related to histological or functional characteristics of the muscle.