Neuronal differentiation is accompanied by increased levels of SNAP-25 protein in fetal rat primary cortical neurons: implications in neuronal plasticity and Alzheimer's disease.

Alzheimer's disease (AD) is accompanied by progressive memory loss and decline in general cognitive abilities. Neuropathological hallmarks include amyloid plaque formation, neurofibrillary tangles, and neuronal and synaptic loss. To improve research models in AD, we have characterized several aspects of the primary rat neuronal cell culture model, which relate directly to the study of neuroexocytosis, neuronal plasticity, and amyloidosis. We have attempted to isolate and assess the neuronal enrichment of a primary cortical cell culture by morphological and molecular techniques, following progress of these cultured cells for up to 18 days in culture to identify the optimum timeframe for the manipulation and data collection in these cells. We observed maximum neuronal differentiation around day 15, which was in decline by day 18, thus, the critical window for manipulations in these cultures seems to be between days 12-15. The substantial increase in neuritic length and density was apparent at very early time points and peaked at day 15. In parallel to morphological assessments, we measured levels of a group of selected neuronally important proteins, including cytoskeletal and synaptic proteins. Change in the levels of cell-associated APP and synaptophysin were not as dramatic as that of SNAP-25 or secreted APP. Notably, this increased differentiation is accompanied by a dramatic increase in levels of SNAP-25 protein, which peaked at day 15 and declined thereafter. These results suggest that this neuronal population contains quantifiable presynaptic terminals. Thus, the establishment and molecular characterization of this neuronal model would have many implications in neuroscience research including synaptic differentiation and neuronal plasticity and for the evaluation of pharmacological interventions in the disease process.