SYNAPSE LOSS AND GLIOSIS IN THE MOLECULAR LAYER OF THE CEREBRAL-CORTEX IN ALZHEIMERS-DISEASE AND IN FRONTAL-LOBE DEGENERATION

Changes in density of synapses and astrocytes in the molecular layer o f the frontal and parietal cortex were compared in Alzheimer's disease (AD) and frontal lobe degeneration of non-Alzheimer type (FLD). The i nvestigation was limited to the molecular layer because it is possible in this part of the cortex to measure changes in synapses and astrocy tes without contamination by nerve cell body changes. In the frontal p ole synapse density declined by 40% in both FLD and AD whereas in the parietal area there was a 50% decrease in synapse density in AD but no significant change in FLD. Number of astrocytes showed an inverse rel ationship to Synapse density. There was a significant increase in astr ocytes in the frontal cortex in both FLD and AD but in the parietal co rtex such an increase was seen only in AD. These results confirm previ ous reports of synapse loss in AD and demonstrate a similar loss in FL D in the frontal, but not parietal, cortex. The findings underscore th e regional pattern changes of FLD, previously shown for other paramete rs, and its difference from that of AD. We propose that these changes in molecular layer may be representative of the pathology (and the fun ctional deficit) within the underlying cortical layers.