On the question of nomenclature of homologous subdivisions of the inferior olivary complex.

The wide variety of terms, or other designations, that have been applied to the mammalian IO have been described above and are summarized in Tables I-IV. Although divergent in their general character there are some common threads that can be used to weave an acceptable and appropriate set of terms that can be applied to most, if not all, mammals studied to date. Concerning the MAO it is clear that there are six principal subdivisions of this part of IO (Table II A, II B). In addition to individual descriptive terms (such as 'ventral part') they have been designated as "subgroups", "cell groups", or "subnuclei" by various investigators. Since MAO, by its name (medial accessory nucleus) is already identified as a subdivision of IO, we suggest that the term 'subgroup' is appropriate to specify further subdivisions of this nucleus. With this in mind we suggest the following nomenclature for the MAO, subgroups, a, b, c (nucleus beta), and d (dorsal cap), the vlo, and dmcc. This is obviously a combination of styles currently in use yet when used together seem most appropriate for several reasons. First, the terms a-d have gained wide acceptance; acceptable equivalent terms for c and d are nucleus beta and dorsal cap, respectively. Second, this method method will accept present opinions concerning probable subdivisions of each subgroup, or future studies which may show that such further subparts exist. For example, such subdivisions can be designated as a and a1 (as is currently done in certain marsupials), b and b1 and so forth. Such an approach would also accommodate the suggestion that subgroup d (dorsal cap) in certain primates consists of two parts. It has been suggested that nucleus beta and subgroup c are separate entities in rat. However, the overwhelming opinion from studies on a variety of other forms is that these are separate terms for the same cell group. One could argue that nucleus beta in rat is subgroup c and what has been called c could be designated c1. Third, the terms vlo (ventrolateral outgrowth) and dmcc (dorsomedial cell column) have gained wide acceptance and, in our opinion, are preferable to other designations. To date no subdivisions of either of these cell groups have been proposed. In addition, the terms 'cell group g' and 'subnucleus g' have been used to describe parts of DAO and MAO, respectively. Consequently, continued use of this designation may confuse the terminology issue more than clarify it.(ABSTRACT TRUNCATED AT 400 WORDS)