RESUMO
The red nucleus is one of the most important structures in the midbrain tegmentum. It plays an important role in the control of motor activities. The aim of the present work is to demonstrate the structure of the red nucleus and the characteristics of its constituent neurons during the various stages of postnatal development, it also includes the study of the ageing effect on the features of its cells. In this work, a total number of 40 albino rats was used. The following postnatal age groups of animals were studied; newly born, seven days, fifteen days and three months old [adult rats] in addition to the aged group of animals [two years old rats]. Animals were sacrificed and the midbrain region was dissected. In each age group, three midbrain specimens were processed to be studied by Einarson's Gallocyanin stain and another three specimens were processed to be studied by Golgicox method. The ultrastructural study for the cells of the red nucleus was done by transmission electron microscope. By using Gallocyanin stain, the red nucleus appeared as a circumscribed mass of cells. The caudal magnocellular part was composed mainly of large neurons and few medium and small sized neurons. The rostral parvocellular part consisted mainly of medium and small sized neurons. The cellular content of Nissl granules increased gradually from the newly born age up to the adult stage. In the aged group of animals, the cells of the red nucleus appeared to be lightly stained as compared to the adult animals indicating loss of Nissl granules. Golgi stain revealed that the caudal magnocellular part of the red nucleus was formed of different types of cells [multipolar, pyramidal and fusiform cells]. Their nerve processes showed gradual increase in the length and branching with the progress of age up to the adult stage. In the aged group of animals, these neurons showed a decrease in the extension of the nerve processes as compared to the adult group. The ultrastructural study of the caudal magnocellular part of the red nucleus in the adult animals revealed that the large neurons were characterized by the presence of rounded nucleus while the medium sized neurons had an invaginated nucleus. The cytoplasm of these cells was rich with ribosomes, rough endoplasmic reticulum and mitochondria. Several types of axosomatic synaptic terminals appeared to be present. In the aged animals, the ultrastructural study of these cells showed marked decrease in the amount of ribosomes and rough endoplasmic reticulum as compared to the adult animals. There was also accumulation of lipofuscin granules in their cytoplasm. It was concluded from this study that during the development of the red nucleus, its constituent neurons showed a progressive increase in their content of Nissil granules from the newly born age up to the adult stage. Their nerve processes also showed increase in the extension and branching. The wide variety of synaptic terminals with rubral neurons indicated the presence of several sources involved in the integration of descending motor information. In the aged animals, the rubral neurons showed several degenerative changes that could lead to impairment of motor activities