Glycogen, its transient occurrence in neurons of the rat CNS during normal postnatal development

Abstract

Progressive changes in the postnatal incidence, distribution and duration of glycogen in neurons of the pons, medulla and spinal cord were studied by light and electron microscopy using cytochemical and quantitative methods. Albino rats of 11 ages ranging from new-born to adult were used for this investigation. Methacrylate sections, stained with periodic acid Schiff-dimedone (PAS) were surveyed to identify nerve cell groups containing the polysaccharide, glycogen. The PAS reaction was positive in neuronal cell groups of the hypoglossal nucleus, the mesencephalic nucleus of V, nucleus ambiguus, the abducens nucleus, the facial motor nucleus and anterior horn cells of the spinal cord. The intensity and duration of the PAS reaction appeared greatest in the hypoglossal nucleus. Neurons of the mesencephalic nucleus of V demonstrated a reaction of moderate intensity and duration. The remaining nerve cell groups exhibited a weak, diffuse reaction of brief duration. Postnatal differences in the incidence and patterns of disposition of glycogen were quantified using ultrathin sections of the hypoglossal nucleus, the site richest in glycogen. The presence of glycogen was verified by the periodic acid-thiosemicarbizide-silver proteinate (PA-TSC-SP) ultracytochemical stain. The incidence of glycogen in neuronal perikarya of hypoglossal nuclei was related to age. All neurons contained some glycogen during the first postnatal week. By 24 days postnatal (dpn), the majority of hypoglossal neurons lacked glycogen and all neurons of adult rats were glycogen-free. Likewise, the distribution of glycogen particles varied with age. At birth, two perikaryal zones served as the primary sites for glycogen localization: the juxtanuclear and marginal regions. Postnatally, changes in the concentration and patterns of glycogen deposits look place principally during the first postnatal week: large accumulations of free glycogen particles were replaced by a small number of particles, randomly dispersed in the perikaryon. To date, glycogen storage in the developing rat brain has been localized almost exclusively in radial glial cells. The present findings provide the initial ultrastructural demonstration of the temporary storage in and subsequent depletion of glycogen from neurons in the brainstem and spinal cord of early postnatal rats.