Intralaminar Distribution of Neurotransmitter-Related Enzymes in Cerebral Cortex of Alzheimer’s Disease

The intralaminar distribution of choline acetyltransferase, galactocerebrosides, gangliosides and proteins were determined in frontal (Brodmann’s area 9) and temporal (Brodmann’s area 22) cortices from subjects with autopsy-proven Alzheimer’s disease and controls matched for sex, age and postmortem delay. In normal brain choline acetyltransferase (CAT) activity was higher in the II and IV layers in the temporal cortex, while in frontal cortex CAT activity was relatively high in the II–III layer, appearing as a single peak. The intracortical distribution of galactocerebrosides normally shows a trend to a higher activity from the pial surface to white matter either in frontal or temporal cortices. Higher concentrations of gangliosides were associated with the cell body layers in either frontal or temporal cortices. In either frontal and temporal cortices from 5 patients with Alzheimer’s disease the pattern of intralaminar distribution of CAT activity was completely disrupted and it was significantly lower than in all cortical layers of the controls. Galactocerebrosides concentration was significantly decreased in the lower layers (IV, V and VI) in both frontal and temporal cortices and ganglioside sialic acid concentration was also decreased in the Alzheimer brain consistently in the lower (III–IV) layers of the frontal and temporal cortices. These observations indicate a widespread involvement of cholinergic activities through all cortical layers. However, the selective decrease in galactocerebroside concentration in the lower layers (IV–VI) suggests a selective loss of ascending fibers from subcortical nuclei. The decreased concentration of ganglioside sialic acid in lower layers suggests a selective axo-dendritic degeneration in these laminae of frontal association and temporal cortex in Alzheimer’s disease.