Topographic organization of substance P and monoamine cells in the ventral medulla of the cat.

A topographic map of the substance P and monoamine neurons in the ventrolateral medulla of the cat has been constructed from peroxidase anti-peroxidase immunohistochemically stained sections. The coordinates of this map use the foramen cecum of the medulla oblongata (i.e. the triangular depression at the junction between the caudal boundary of the pons and the rostral limit of the median fissure between the pyramidal tracts) as the zero point. Two distinct groups of substance P neurons have been found: a rostral group lies ventral to the facial nucleus and a caudal one is found ventrolateral to the inferior olivary nucleus. Two dopamine beta-hydroxylase-containing cell groups were identified that correspond to the A1 and A5 cell groups. The A5 cell group lies dorsal, lateral and caudal to superior olivary nucleus. The A1 cell group lies approximately 4.0-5.0 mm lateral to the midline at the level of the inferior olive; these cells lie mainly dorsolateral to the region of the magnocellular division of the lateral reticular nucleus. The B1 and B3 serotonin (5-hydroxytryptamine) cell groups of the ventrolateral medulla appear to form a continuous column with a rostral and a caudal swelling. The rostral group begins at the level of the facial nucleus (approximately 4 mm caudal to the foramen cecum) and is concentrated in the area just lateral to the pyramidal tract. It becomes reduced in size approximately 8.0 mm caudal to the foramen cecum, and then enlarges to form a caudal group (approximately 10 mm caudal to foramen cecum). Portions of this column overlap with the caudal substance P cell group. The C1 cell group lies in a restricted zone approximately 4.0 mm lateral to the midline at the level of the rostral part of the inferior olivary nucleus.