RESUMO
The mammillary body is the most prominent structure in the caudal hypothalamus of rats as it is involved in a variety of associative and memory processes. The aim of this study was to throw light on the postnatal developmental and aging changes of the mammillary body nuclei in the rat. A total number of 65 albino rats were used in this work. The age groups of the animals included new born, fifteen days, one month, two months and two years old rats. Specimens were processed for ordinary histological study and stained with Gallocyanin chrom-alumstain and Golgicox method. Ultrastructural study with the aid of the transmission electron microscope was done for the adult and aged rats. The results of this study revealed that the mammillary body is composed of a lateral and a medial mammillary nucleus, the latter has been subdivided into four subnuclei: pars lateralis, pars medianus, pars medialis, and pars posterior. The cells are either medium-sized or small and the sizes differ, among different subnuclei. The largest cell sizes are found in the lateral mammillary nucleus. These cells have long branching dendrites that are often beaded with no spines. Most cells in the medial mammillary nucleus are characterized by long branching dendrites and exhibit numerous spines. Cells of the mammillary nuclei are characterized by closely apposed neuronal somata and imaginations of the nuclear membrane. There are also various types of axosomatic synaptic terminals with the mammilary neurons. The neurons of the mammillary nuclei showed increase in the amount of Nissl material, progressive increase in thickness, extension and branching of their dendrites with development, there is also apparent increase in the size of the mammillary body. In the aged rat, there are some degenerative changes in the mammillary neurons in the form of apparent reduction in the size of the mammillary body relative to the adult age. There is decreased staining affinity of the cytoplasm, extensive decrease in the thickness and extension of the dendrites with decrease in the amount of somatic and dendritic spines. Most neurons reveal progressive accumulation of lipofuscin pigment and marked imaginations of the nuclear membrane with the progress of age. As the mammillary body is involved mainly in memory, this function could be expected to decline with age as a consequence of these degenerative changes