Regeneration And Plasticity In The Olfactory System Of The Rat

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The receptor cells in the olfactory epithelium have unmyelinated axons that terminate within glomeruli of the olfactory bulb. It is generally believed that the receptor cells die when their axons are cut and that the axons of newly formed receptor cells are responsible for reinnervating the glomeruli. The aim of this investigation was to examine the growth of olfactory axons after transection in the peripheral or central nervous system and to examine the effects of axonal injury on the receptor cells.;In 35 rats the olfactory nerves were transected on the intracranial side of the cribriform plate. Most glomeruli were denervated in rostrodorsal portions of the bulb by 2 to 3 weeks, and by 42 days all glomeruli were reinnervated. Degenerating cells were present in the olfactory epithelium during the first 10 days, and by 31 days the epithelium was normal. In the olfactory epithelium of 4 rats, degenerating cells were also observed 7 days after small pieces of tissue were removed from the dorsal surface of the bulb.;When a transverse incision was made in the dorsal surface of the bulb in 41 rats the glomeruli caudal to the incision were devoid of olfactory axons by 14 days, but abnormalities were found in the olfactory epithelium only from the 21st postoperative day onwards. Reinnervation was complete by the end of the 4th week. The axons responsible for this reinnervation did not grow across the lesion.;One month after a transverse incision was made in the dorsal surface of the bulb in 2 rats, crystalline horseradish peroxidase (HRP) was applied over a second incision made rostral to the first. The glomeruli caudal to the initial incision were anterogradely labelled with HRP. This study demonstrated that at least part of the reinnervation to the glomeruli caudal to a transverse incision is by axons that travel in the nerve fibre layer rostral to the lesion.;These results indicate that death of the receptor cells is not an inevitable consequence of cutting their axons. It is suggested that the olfactory axons are capable of axonal regeneration and that the death of receptor cells that does occur after axotomy is due to the failure of their axons to regenerate around, or across, the lesion.

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