Electron microscopy of plasticity in XXXX olfactory cortex.

@entity35 @entity75 @entity16843
Electron microscopy (EM) is being used to study the ultrastructural basis for the age-dependent reorganization of afferents in the olfactory cortex (OC) of @entity35 after deafferentation of the area by removal of the ipsilateral olfactory bulb (OB). The double-lesion technique was used with a @entity75 of the OB at various @entity16843 ( @entity16843 ) ages between @entity16843 0 and 30 and in the adult ( @entity16843 100). After appropriate survival times to remove @entity75 , a second lesion was placed in the ipsilateral OC. One to 3 days later the tissue is prepared for EM with emphasis on a study of changes in the superficial and deep dendritic layer (Ia and Ib respectively) rostral to the lesion. In control litter mates with both OBs intact, but with a single OC lesion only, degenerating synaptic terminals occur onto dendritic spines and branches only in deeper Ib. However, in adults with @entity75 at @entity16843 0-9, OC lesions produce degenerating terminals throughout Ia and Ib including immediately subjacent to the pia. In Ia degenerating terminals are greatly reduced in the @entity16843 13 group and rare to absent in experiments with @entity75 at older ages ( @entity16843 30-100). Electron-dense debris within glia occurs throughout layer I in each double-lesion group but is greatest in experiments with @entity75 at older ages. Some transsynaptic alterations are seen throughout, especially in the @entity16843 30-100 group even at a distance from the OC lesion. The results support earlier light microscopic (LM) findings, suggesting @entity16843 9-13 as critical ages for developmental plasticity and prove that at least in the younger ages, synapses are involved in the phenomenon. This may be explained by either reinnervation of deafferented sites or persistence of synapses that would otherwise have been eliminated by afferents from the OB. In addition, some of the LM degeneration particles probably are engulfed masses of debris and not synaptic structures, especially in cases which were operated at older ages and survived for 3 days. The various afferent pathways involved in the events as well as factors that limit the phenomenon in older ages are discussed.
