Olfactory function after bulbectomy.
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Animals↗
Biomedical subjects
G A Graziadei
Publications and source records attributed to G A Graziadei.
Neurogenesis of sensory neurons in the primate olfactory system after section of the fila olfactoria.
Axotomy of the olfactory sensory neurons in the adult primate squirrel monkey induces retrograde degeneration of the perikarya in the nasal neuroepithelium. The process of neuronal degeneration is rapid and by the 10th day the olfactory neuroepithelium is deprived of all mature neurons. Basal cells, supporting cells and the Bowman's glands are unaffected by the surgical procedure. The degeneration of the neurons is followed by intense mitotic activity of the basal cells of the neuroepithelium. At 30 days survival several young, mature neurons are present again in the neuroepithelium. At 60--90 survival days the neuroepithelium reacquires a population of neurons similar to controls. The persistence of neurogenesis and the replacement of experimentally degenerated neurons in an adult, non-human primate is briefly discussed.
Animals↗
The olfactory marker protein in the olfactory system of the mouse during development.
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Aging↗
Neurogenesis and neuron regeneration in the olfactory system of mammals. II. Degeneration and reconstitution of the olfactory sensory neurons after axotomy.
This report describes the retrograde degeneration affecting olfactory sensory neurons of rats after severance of their axons and illustrates the reconstitution of new neurons originating from stem cells located at the base of the olfactory neuroepithelium. Degeneration of the mature, axotomized neurons, signalled by an increased electron density of their cytoplasmic matrix and by the appearance of lipofuscin-like granules, can be detected in the neuroepithelium as early as 24 h after surgery and becomes conspicuous between the second and the third day. Degenerating neurons can be observed in decreasing number up to the tenth post-operative day. They are removed by macrophages which invade the epithelium. The reconstitution of new neurons begins to occur after eight days, when the stem cells undergo vigorous mitotic activity and differentiate into neurons. The morphology of the reconstituted neurons has been described in detail at different stages of their maturation. After 30 days, the olfactory epithelium appears similar to controls. On the basis of both morphological (in rats) and autoradiographic ( in mice) observations, the basal cells have been recognized as stem cells of the olfactory neurons.
Animals↗
Neurogenesis and neuron regeneration in the olfactory system of mammals. I. Morphological aspects of differentiation and structural organization of the olfactory sensory neurons.
The neurogenetic process leading to the formation of primary sensory neurons persists into adult life in the olfactory epithelium of mammals. The morphological stages of maturation and ageing of this exceptional neuron have been described both at light and electron microscopical levels. For descriptive purposes the neural elements have been classified as: (1) basal cells proper, (2) globose basal cells, and (3) neurons. Intermediate stages, however, have been identified. Autoradiographic observations complement the morphological studies and provide a time sequence of the morphological stages leading to the mature neurons. A typical columnar arrangement of the sensory neurons has been described. Furthermore, active and quiescent zones have been recognized in the neuroepithelium. In the active zones the neurogenetic process is vigorous, and the zones are characterized by the presence of immature elements. However, in the quiescent zones there exists a population of mature elements while immature neurons are sparse.
Animals↗
Regeneration of olfactory axons and synapse formation in the forebrain after bulbectomy in neonatal mice.
We removed the right olfactory bulb in neonatal mice, leaving the bulb on the left side intact as an internal control. At 5 days of survival time, we observed that the right cerebral hemisphere was displaced forward to occupy the region made vacant by removal of the bulb. The frontal cortex was, consequently, in close proximity to the lamina cribrosa. As a result of bulb ablation and severance of the fila olfactoria, the sensory perikarya underwent total retrograde degeneration, which peaked at 8 days. New neurons differentiated in the neuroepithelium from basal stem cells and, at 30 days of survival, mature sensory neurons were reconstituted. These new elements sent their axons through the lamina cribrosa to reach the protruding cerebral hemisphere, penetrating it and forming glomeruli-like structures directly in the host tissue. The "glomerulization" of the sensory fibers persisted and actually expanded between 60 and 120 days. The new glomeruli were organized intimately within the brain tissue, and large neurons of the cortex were observed to be in close proximity. Ultrastructural observations of the newly formed glomeruli demonstrated that typical sensory axon terminals profusely branched and synapsed with unidentified postsynaptic processes that penetrated the glomeruli from the surrounding cerebral tissue.
Animals↗
Observations on the ultrastructure of ganglion cells in the circumvallate papilla of rat and mouse.
Ganglion cells in the circumvallate papilla of adult rodents are described as typical autonomic neurons. Some neurons are aggregated to form a discrete structure in the base of the papilla; others are scattered through the core, along the nerve bundles, and particularly near the dome. The term "circumvallate ganglion" is applied to the entire population. Satellite cells completely ensheathe each neuron. Preganglionic fibers, containing clear vesicles, synapse on the soma and stumpy dendrites of the neurons. Axons, containing dense-cored vesicles, are observed in close proximity to the neurons. However, these fibers do not establish true morphological synaptic contacts with the neurons. We have not observed serial or reciprocal synapses on or in the vicinity of the ganglion cells. The hypothesis that the axons of the circumvallate ganglion neurons act as parasympathetic vasodilators is indicated by the proximity of the two structures and by nerve terminations on the arteriole muscle cells. Direct modulation of taste transduction by these neurons is ruled out.
Animals↗