Thickness of ependyma and alveus on the hippocampus of adult madras red sheep (Ovis aries)

Abstract

The study was conducted on hippocampus (N=18) collected from six-month-old, eight-month-old and twelve-month-old adult Madras Red sheep. The hippocampus was semicircular in shape located behind the caudate nucleus in the floor of the lateral ventricle. The cytoarchitecture of the hippocampus appeared as a seven-layered structure enclosing the dentate gyrus within it, on its inferior side. It appeared like a comma shaped structure composed of neuron and nerve fibers and glial cells forming a curvature over the dentate gyrus. The cornu ammonis of the hippocampus was divided into four distinct regions in cross section as CA1, CA2, CA3 and CA4 segments which showed variation in the arrangement and thickness of the layers observed. All the layers of the hippocampus, the ependyma, alveus, stratum oriens, stratum pyramidale, stratum radiatum, stratum lacunosum and stratum molecular were identified. The hippocampus gyrus was lined by the ependyma which was composed of low cuboidal cells with oval nuclei. Inner to the ependymal layer, the alveus was made up of myelinated nerve fibers running parallel to the surface. The third layer beneath the alveus formed the stratum oriens which consisted of cell bodies of inhibitory basket cells like neurons and horizontal triangular cells. The stratum pyramidale consisted of pyramidal shaped neurons distributed in this strata. Stratum radiatum was composed of a complex network of commissural fibre and septal fibres. Stratum laucunusom situated beneath the radiatum was composed of collateral nerve fibres, which was grouped with the layer beneath made up of granular or stellate cells and referred as stratum lacunosum moleculare. The four fields of the cornu ammonis CA1, CA2, CA3 and CA4 were observed.