Inhibition of the Polyamine System Counteracts β-Amyloid Peptide-Induced Memory Impairment in Mice: Involvement of Extrasynaptic NMDA Receptors

In Alzheimer's disease (AD), the beta-amyloid peptide (A beta) has been causally linked to synaptic dysfunction and cognitive impairment. Several studies have shown that N-Methyl-D-Aspartate receptors (NMDAR) activation is involved in the detrimental actions of A beta. Polyamines, like spermidine and spermine, are positive modulators of NMDAR function and it has been shown that their levels are regulated by A beta. In this study we show here that interruption of NMDAR modulation by polyamines through blockade of its binding site at NMDAR by arcaine (0.02 nmol/site), or inhibition of polyamine synthesis by DFMO (2.7 nmol/site), reverses A beta(25-35)-induced memory impairment in mice in a novel object recognition task. Incubation of hippocampal cell cultures with A beta(25-35) (10 mu M) significantly increased the nuclear accumulation of Jacob, which is a hallmark of NMDAR activation. The A beta-induced nuclear translocation of Jacob was blocked upon application of traxoprodil (4 nM), arcaine (4 mu M) or DFMO (5 mu M), suggesting that activation of the polyamine binding site at NMDAR located probably at extrasynaptic sites might underlie the cognitive deficits of A beta(25-35)-treated mice. Extrasynaptic NMDAR activation in primary neurons results in a stripping of synaptic contacts and simplification of neuronal cytoarchitecture. A beta(25-35) application in hippocampal primary cell cultures reduced dendritic spine density and induced alterations on spine morphology. Application of traxoprodil (4 nM), arcaine (4 mu M) or DFMO (5 mu M) reversed these effects of A beta(25-35). Taken together these data provide evidence that polyamine modulation of extrasynaptic NMDAR signaling might be involved in A beta pathology.