Qualitative and Quantitative Studies of the Inferior Olivary Complex in the Water Buffalo (Buballus bubalis)

Abstract

ABSTRACT. The shape and neuronal number of the inferior olivary complex (IOC) were determined in the water buffalo (Buballus bubalis). The configuration and interrelations of the IOC compartments were ascertained by investigating serial sections through the whole rostrocaudal extent of the IOC. Nissl-stained celloidin sections of six water buffalo's brainstems were used. The IOC in the water buffalo consisted of three major nuclei and four small cell groups. The medial accessory olivary nucleus (MAO) had the longest rostro-caudal extent as well as the highest number of neurons (98,000 ± 3,000). Although the total area of the principal olivary nucleus (PO) was smaller than the area of the dorsal accessory olivary nucleus (DAO), the PO had the second largest neuronal number. The total number of neurons on both sides of the IOC was 210,000 ± 7,000 cells. The average neuronal density was 3,000 cells/mm 3 . Although the size of the PO relatively increases while the size of MAO decreases with the development of the cerebellar hemispheres, the IOC in most mammals maintains a similar structure except for the higher primates and marsupials. The water buffalo IOC showed morphological similarities to the almost all mammalian IOC including rats as follow; the main part of the MAO consists of three subgroups (a, b and c), the DAO is Boomerang-shaped while the PO is a simple U-shaped structure. KEY WORDS: brainstem, morphology, neuronal number.J. Vet. Med. Sci. 69(2): 143-147, 2007 Although, the morphology of the inferior olivary complex (IOC) has been demonstrated in many mammals [2-6, 10, 15, 21-23, 27-29, 33, 35], there have been relatively few studies on this nuclear complex in large animals including the water buffalo (as a prevalent ruminant in Asia and Africa). In most of studied mammals, the IOC is divided into three main nuclei; a medial and dorsal accessory olivary nuclei (MAO and DAO, respectively), and a principal olivary nucleus (PO) and four small cell groups; the dorsal cap (DC), the ventro-lateral outgrowth (VLO), the nucleus b and the dorso-medial cell column (DMCC). However, the marsupial's IOC consists of the same nuclei but their relative positions are different from other mammals [23, 35].Recently, the IOC has been compartmentalized by the olivocerebellar projections using tracer techniques [33]. Consequently we can correlate roughly the morphological structures that are shown by Nissl-stained sections, with the compartments by neural circuits of the IOC. However, these tract tracing methods are limited in small mammals including rats, rabbits and cats. In this study we described the morphology of the IOC in the water buffalo, to which it is very difficult to apply tract tracing methods for size, and compared the IOC of the water buffalo and other mammals. We discussed that neuroanatomical results of the IOC in small mammals could be applicable to the large mammals like the water buffalo.It is generally recognized that the IOC is the sole source of the climbing fibers innervating the Purkinje cells of...