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Effects of sensory deprivation on the developing mouse olfactory system: a light and electron microscopic,
Abstract:
Closure of the nostril by electrocauterization on postnatal day (PN) 1 or 2 was used to study effects of olfactory deprivation on developing olfactory epithelium (OE) and bulb (OB) in CD-1 mice. No damage was observed in OE sections 1 or 3 days after closure, and at PN 30 no difference was found in the number of OE receptors between closed and open sides. Odor deprivation and a decrease in functional activity in experimental bulbs was evident from deoxyglucose autoradiographs at PN 21 and PN 30. At PN 30 deprived bulbs appeared smaller than nondeprived bulbs. Nissl stains revealed normal cytoarchitecture, but a protargol stain demonstrated fewer intraglomerular dendrites in deprived bulbs. At PN 30, volumes of deprived bulbs were 26% smaller than nondeprived bulbs. The volume of each bulbar lamina was 13 to 35% smaller than the comparable nondeprived lamina except for the ventricular/subependymal zone which was not significantly different between bulbs. Volumes of bulbs contralateral to the closed naris and the volumes of their laminae were not significantly different from control bulbs, suggesting no hypertrophy of nondeprived laminae. Deprivation did not affect the number of mitral cells seen at PN 30, their nuclear size, or their number of nucleoli. Lateral olfactory tract cross-sectional area was also unaffected by deprivation. Mitral cell perikaryal size, however, was smaller in deprived bulbs. Soma surface areal density of deprived mitral-to-granule cell synapses in deprived bulbs was 65% of the nondeprived density, while the density of granule-to-mitral cell synapses was only 46% of the nondeprived density. It is concluded that neonatal naris closure brings about a functional deprivation of the OB without receptor degeneration. Neonatal olfactory deprivation affects the perikaryal surface area but not the number of mitral cells. Also, deprivation markedly affects the reciprocal synapses between mitral and granule cells. Olfactory sensation thus appears necessary for normal development of OB neurons and synapses.
Insights
Neonatal olfactory deprivation in mice reduced olfactory bulb volume and altered synaptic density without damaging olfactory receptors. This highlights the necessity of olfactory sensation for normal olfactory bulb development.
Area of Science:
- Neuroscience
- Developmental Biology
- Sensory Systems
Background:
- The olfactory system's development is influenced by sensory input.
- Understanding the impact of early sensory deprivation is crucial for developmental neuroscience.
Purpose of the Study:
- To investigate the effects of neonatal olfactory deprivation on the developing olfactory epithelium and olfactory bulb in mice.
- To determine if functional activity is necessary for the normal maturation of olfactory bulb structures.
Main Methods:
- Neonatal mice underwent nostril closure via electrocauterization on postnatal days 1 or 2.
- Olfactory epithelium and bulb were analyzed using histological stains (Nissl, protargol) and deoxyglucose autoradiography.
- Quantitative measurements of olfactory bulb volume, laminae volumes, mitral cell characteristics, and synaptic densities were performed.
Main Results:
- Olfactory deprivation led to smaller olfactory bulbs (26% reduction) and reduced volumes in most bulbar laminae.
- Deoxyglucose autoradiographs showed decreased functional activity in deprived olfactory bulbs.
- While mitral cell numbers were unaffected, their perikaryal size decreased, and the density of reciprocal synapses between mitral and granule cells was significantly reduced.
Conclusions:
- Neonatal olfactory deprivation causes functional deficits in the olfactory bulb without olfactory receptor degeneration.
- Olfactory sensation is essential for the normal development of olfactory bulb neurons, particularly mitral cells, and their synaptic connections.