Histological Atlas and Morphological Features by Nissl Staining in the Amygdaloid Complex of the Horse, Cow and Pig

Abstract

There are no reports about the amygdaloid complex in horses, cows and pigs. The amygdaloid complex is divided into many subnuclei from the point of histology, and the purpose of this study was to clarify its features by comparison among horses, cows and pigs. Using the Nissl staining method, we examined coronal serial sections of brains from the three species. The division of the amygdaloid subnuclei was performed on the magnified photos and three-dimensional analysis was also performed for the three species. The shape of the amygdala in the horse and cow was an anterior ellipsoid, long and slender in the dorso-ventral direction, posteriorly. In the pig, it was long and slender in the dorso-ventral direction as a whole. The volume of the amygdala in the horse as a percentage of cerebral volume was the biggest among the three species. We divided the amygdala into 27 subnuclei and these subnuclei were classified into 11 subnuclei groups. Features of some subnuclei resembled those of other species, such as rabbit, cat and monkey. Taking into consideration brain development, it was clear that the shapes of the subnuclei were fairly reflected by the brain development within the skull. From the results of three-dimensional analysis, the amygdala was mainly occupied by the lateral and basal nuclei, each occupying about 30% of the amygdala. Features of each species were that the relative size of the posterior cortical nucleus was high in the horse and cow, and the relative size of the amygdalohippocampal area was high in the pig. We concluded that the features of the subnuclei may be related to the functional development.