Difference in ability for extracellular Zn 2+ influx between human and rat amyloid β 1-42 and its significance.

The accumulation of amyloid-β1-42 (Aβ1-42 ), a constituively-generated peptide, in the brain is considered an upstream event in pathogenesis of Alzheimer's disease. Aβ1-42 -induced pathophysiology has been extensively studied in experimental mice and rats. However, neurotoxicity of murine Aβ1-42 is much less understood than human Aβ1-42 . Here we report difference in ability for extracellular Zn2+ influx into dentate granule cells of rats between human and rat Aβ1-42 and its significance. Human Aβ1-42 rapidly increased intracellular Zn2+ , which was determined with intracellular ZnAF-2, in dentate granule cells, 5 min after injection of Aβ1-42 (25 μM, 1 μl) into the dentate gyrus, while rat Aβ1-42 did not increase intracellular Zn2+ . In vivo perforant pathway LTP was attenuated under pre-perfusion with 5 nM human Aβ1-42 in artificial cerebrospinal fluid (ACSF) containing 10 nM Zn2+ , recapitulating the concentration of extracellular Zn2+ , but not with 5 nM rat Aβ1-42 in ACSF containing 10 nM Zn2+ . The present study suggests that rat Aβ1-42 has lower affinity for extracellular Zn2+ than human Aβ1-42 and does not capture Zn2+ in the extracellular compartment, resulting in no significant effect on cognitive activity of rat even in the range of very low nanomolar concentrations of endogenous Aβ1-42 .