Afferent and efferent connections of the area postrema demonstrated by the horseradish peroxidase method

: The previous autoradiographic study of the efferent connections of the arca postrema have been completed by using horseradish peroxidase (H.R.P.) as a marking agent. These two labelling techniques have made it possible to determine two categories of structures connected with A.P.: those with afferent connections (Nucleus ambiguus), or efferent connections (mesencephalic nucleus of V, Locus coeruleus, griseum centrale and inferior and superior colliculi) and those having both types of connections (Nucleus tractus solitarii (N.F.S.), Dorsal vagal nucleus, nucleus intercalatus, hypoglossal nucleus). The afferent and efferent pathways of the A.P. identified with H.R.P. coincide with the catecholaminergic pathways demonstrated in the rat by Lindvall and Bjorklund (1974).