Age-dependent changes in axonal transport and cellular distribution of Tau 1 in the rat basal forebrain neurons

Basal forebrain (BF) cholinergic neurons are prone to degeneration due to age-dependent impairment of uptake and retrograde axonal transport of NGF. Modification and intracellular redistribution of cytoskeletal tau proteins could be responsible for this process. In this study we injected fluorogold (FG) into neocortex and hippocampus of young and aged rats. The number of neurons retrogradely labeled with FG in subdivisions of BF was significantly lower in aged rats than in young ones. We also characterized the distribution of Tau 1 in cellular compartments of BF and hippocampal neurons. Tau 1 immunostaining restricted to neuritic structures was observed in neurons of septo-hippocampal pathways in young rats. In contrast, aged rats displayed the presence of Tau 1 isoform mainly in the somatodendritic compartment of BF neurons. The findings demonstrate that in aged rats reduced retrograde labeling of BF neurons coincide with lower expression of cholinergic markers and is accompanied by altered cellular distribution of Tau 1.