Hippocampal granule cell loss in human chronic alcohol abusers

Chronic alcohol abuse causes cognitive impairments associated with neurodegeneration and volume loss in the human hippocampus. Here, we hypothesize that alcohol reduces the number of granule cells in the human dentate gyrus and consequently contribute to the observed volume loss. Hippocampal samples were isolated from deceased donors with a history of chronic alcohol abuse and from controls with no alcohol overconsumption. From each case, a sample from the mid-portion of hippocampus was sectioned, immunostained for the neuronal nuclear marker NeuN, and counter stained with hematoxylin. Granule cell number and volume of granular cell layer in the dentate gyrus were estimated using stereology. We found a substantial reduction in granule cell number and also a significantly reduced volume of the granular cell layer of chronic alcohol abusers as compared to controls. In controls there was a slight age-related decline in the number of granule cells and volume of granular cell layer in line with previous studies. This was not observed among the alcoholics, possibly due to a larger impact of alcohol abuse than age on the degenerative changes in the dentate gyrus. Loss of neurons in the alcoholic group could either be explained by an increase of cell death or a reduced number of new cells added to the granular cell layer. However, there is no firm evidence for an increased neuronal death by chronic alcohol exposure, whereas a growing body of experimental data indicates that neurogenesis is impaired by alcohol. In a recent study, we reported that alcoholics show a reduced number of stem/progenitor cells and immature neurons in the dentate gyrus, hence that alcohol negatively affects hippocampal neurogenesis. The present results further suggest that such impairment of neurogenesis by chronic alcohol abuse also results in a net loss of granule cells in the dentate gyrus of hippocampus.