CONTRIBUTIONS TO THE COMPARATIVE ANATOMY OF THE RETICULAR NUCLEI OF THE BRAIN STEM IN MAMMALS
Authors: Koikegami H. , Ogawa S. , Tanaka K. , Imogawa T. , Mitobe F. 
Published: March 2008

Comparative anatomical observations of the brain stem of the various mammals led us to note some remarks on variance in the cellular elements, the correlation with the central gray or with the posterior hypothalamic nuclei, and on the peculiar cell groups described in the literature. They may be of value for coming experimental researches.

As to the variance of cellular make‐up in various levels of the subnuclei, the minute cell count in such nuclei of rodents reveals that in three main subnuclei, i. e. R.gc, R.P.c and R.P.o of Meessen and Olszewski's denomination in the realm of reticular formation, the total number of cells shows a general tendency of increasing oralward, especially concerning the smaller cell type, while in the parvocellular nuclei, R.pc and R.pca, the smaller cells get reduced at the profit of increasing medium‐sized cells oralward. These variances in the cell types in various sectioning levels concerning each nuclei stand almost in the same relationship in all the animals observed.

Cellular correlations between the midbrain reticular formation and the periaquaeductal gray substance were noticed especially in two places, namely at the meso‐diencephalic and meso‐rhombencephalic regions of transition. In the lastly named region, the attention was given to the so‐called nucleus supratrochlearis bearing several subnuclei in within. The mediodorsal portion of the region is so far somewhat differing in cellular make‐up, as the portion of some animals lets prove resemblance with the reticular nuclei. This homology in cellular make‐up is also traceable in the former region.

The medial and the lateral part of the nucleus loci caerulei embedded in the reticular formation (nucleus ventralis et lateralis brachii of Winkler and Potter) were studied more minutely, where the secondary degeneration occurred seemingly after long survival period following destruction of some parts of the diencephalon, especially of the hypothalmic b‐sympathetic zone. The medial portion, Coe2, seems to receive impulse from the ipsilateral hypothalamic region, while the lateral portion, Coe3, from the contralateral hypothalamic region. Thereby it was pointed out that there still avails dubiousness concerning whether they ought to be looked upon as a part of the nucleus loci caerulei or not.

The nucleus perpendicularis formationis albae was established in cases of several mammals, of all material most distinctly in the Indian elephant. This nucleus seems to stand in correlation particularly intimately with the medial longitudinal bundle, otherwise, with the paramedian reticular nuclei.

In the light of the cellular component of the nucleus retrofacialis and the accessory facial nucleus, we can put aside several types among animal species examined, especially from the view‐point that the former nucleus ought to be accepted as the correspondent to so‐called “dichte Formation” of the ambiguus nucleus in some German authors' interpretation while the latter represents a participant of the facial nucleus to the major part. Concerning the oral part at the least, however, the cells of the so‐called accessory facial nucleus much resemble to the trigeminal motor nucleus in some animals, another time to the large cells of the reticular formation in certain another animals and still another time to cells of the abducens nucleus as was already mentioned from other side.