Parabrachial nuclear complex. A comparative study of its cytoarchitectonics in birds and some mammals including man

The cytoarchitectonic structure of the ncl. parabrachialis of 20 bird species, 17 mammals and man was studied in sections stained with cresyl violet. This comparative study showed the six cytoarchitectonic subnuclei of the ncl. parabrachialis (subncl. medialis, dorsomedialis, dorsalis, lateralis, dorsolateralis and ventralis) to be unevenly developed in the vertebrates under study. The degree of development of the subnuclei was tabulated to bring out the developmental trends of the ncl. parabrachialis in different groups of vertebrates. Only three of the six subnuclei were found enlarged in higher primates and in man--the subncl. dorsolateralis, lateralis and medialis, the latter two (subncl. lateralis and medialis) being also larger in insectivores. The most primitive structure is that of the subncl. ventralis with features very much like those of a small-cell reticular formation. Cytoarchitectonically speaking, the parabrachial subnuclei appear to be of polyphyletic origin: the medial and dorsomedial subnuclei being close to the substantia grisea centralis, the ventral subnucleus to the small-cell lateral reticular formation, and the lateral and dorsolateral subnuclei to the ncl. pedunculo-pontinus.