Alterations in axons and synapses of olfactory cortex following olfactory bulb lesions in newborn rats

Summary The olfactory cortex of rats is being studied at various survival times following deafferentating olfactory bulb ablation on the day of birth. The neonatal axons and synaptic terminals undergo rapid, flocculent degeneration and fragmentation. Most are not electron-dense and therefore probably not argyrophilic at this particular age of the lesion. The degeneration and removal of debris is far more rapid than in adults, yielding a markedly enlarged extracellular space with a relative absence of glia at the vacated postsynaptic thickenings. Denervated postsynaptic thickenings become occupied by neuronal and nonneuronal profiles and profiles of uncertain origin, singly or in various combinations, or the sites may remain partially vacant. One or more axons with synaptic vesicles often aggregated at the site are commonly involved. Certain terminals form contacts on progressively greater lengths of the thickening until typical synaptic contacts predominate by 14 days survival. The results suggest a competitive reinnervation process and provide a fine structural explanation for the events leading to alterations in this pathway following neonatal deafferentation.This project was supported in part by NIH Research Grants DE 04942, awarded by the National Institute of Dental Research, and Grants NS 09678 and NS 04053 from the National Institute of Neurological and Communicative Disorders and Stroke, PHS/DHEWDr. Westrum is also an affiliate of the Child Development and Mental Retardation Center, University of Washington