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

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 olfactory bulb (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 ZnSO{dollar}sb4{dollar} 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 tyrosene hydroxylase (TH) immunoreactivity in the periglomerular cells. The deafferentation resulted in a decrease in the density of serotonergic fibres in the deeper regions of the lesioned OB in adult animals. The density of astrocytes expressing S-100, did not correlate with the density of serotonergic innervation. In contrast to the serotonergic system, the density of nonadrenergic 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. (Abstract shortened by UMI.)...