The effect of peripheral deafferentation on specific axonal systems and glial elements in the main olfactory bulb of the rat

King, Shelley R. (1994) The effect of peripheral deafferentation on specific axonal systems and glial elements in the main olfactory bulb of the rat. Masters thesis, Memorial University of Newfoundland.

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Abstract

Heterotypic collateral sprouting of neurotransmitter systems has been observed in many regions of the CNS following injury. The olfactory bulb (OB) receives direct input from the olfactory epithelium and its neuroanatomy and neurotransmitter content have been well characterized. Thus, the OB may provide a useful cortical model of lesion-induced plasticity. The present study has tested the hypothesis that heterotypic collateral sprouting of specific axonal systems, especially the serotonergic axons from the raphe, will occur following peripheral deafferentation of the OB. In addition, we hypothesized that an increase in the number of astrocytes would occur following deafferentation of the OB. In this study, serotonin, dopamine beta-hydroxylase, glial fibrillary acidic protein (GFAP) and S-100 (serotonergic growth factor) immunocytochemistry was performed to elucidate the response of different axonal systems and glial elements to peripheral deafferentation of the OB. -- Deafferentation of the right OB was achieved by application of ZnSO₄ to the olfactory epithelium (OE) of adult male rats and postnatal day (PND) 10 rat pups. The effectiveness of the lesion was determined by the degree of the loss of tyrosine hydroxylase (TH) immunoreactivity in the periglomerular cells which require the presence of the OE to express the TH phenotype. The deafferentation resulted in a decrease in the density of serotonergic fibres in the deeper regions of the lesioned OB in adult animals which is in contrast to the increase in density evident in the PND 31 animals. The density of astrocytes expressing S-100, a proposed serotonergic growth factor, did not correlate with the density of serotonergic innervation. In contrast to the serotonergic system, the density of noradrenergic fibres in the lesioned OB was increased in the adult animals, but remained unchanged in PND 31 rat pups. The densities of GFAP positive astrocytes in the lesioned OB of adult and PND 31 animals were similar to those of control animals. These results suggest that deafferentation of the OB of adult animals did not induce heterotypic sprouting of intact serotonergic fibres in the three week time period. On the contrary, the serotonergic fibres were selectively decreased, perhaps due to the potential neurotoxicity of zinc to these fibres. It appears, however, that the serotonergic fibres in the younger animals are capable of sprouting in response to OB deafferentation and this response may be related to the indirect neuromodulatory effects of zinc.

Item Type: Thesis (Masters)
URI: http://research.library.mun.ca/id/eprint/5654
Item ID: 5654
Additional Information: Bibliography: leaves 111-127.
Department(s): Medicine, Faculty of
Date: 1994
Date Type: Submission
Library of Congress Subject Heading: Central nervous system--Regeneration; Olfactory nerve; Sertoninergic mechanisms; Axons; Neuroglia
Medical Subject Heading: Central Nervous System; Olfactory Bulb

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