ABSTRACT
The cervical, thoracic, or lumbar spinal gray was injected with HRP or WGAHRP unilaterally in 18 adult rabbits and the anterograde labeling was traced in the pontine nucleus and the caudal pontine ventrolateral tegmentum.In the pontine nucleus labeled terminal arborizations were found in its caudal 1/3, distributing in the paramedian nucleus, the dorsal part of peduncular nucleus and the dorsolateral nucleus. In the ventrolateral tegmentum four small cell groups were found labeled which were temporarily denominated as VLPT_(1～4) groups. In all locations labelings were found bilaterally and no apparent somatotopical localization could be identified.The cytoarchitecture of VLPT_(1～4) was studied on Nissl sections and their relationship with Meessen and Olszewski's (M-O's) "k" and "m" groups and with pontobulbar body was discussed. VLPT_2 (corresponding to the ventral part of M-O's "k") and VLPT_3 (corresponding to a part of M-O's "m") join each other to form one group which then merges into the dorsolateral nucleus of the pontine gray. They apparently form a part of the pontobulbar body.