Enhanced long-term potentiation in the hippocampus of rats expressing mutant presenillin-1 is age related

Hippocampal interneuron loss in an APP/PS1 double mutant mouse and in Alzheimer's disease

Hippocampal atrophy and neuron loss are commonly found in Alzheimer's disease (AD). However, the underlying molecular mechanisms and the fate in the AD hippocampus of subpopulations of interneurons that express the calcium-binding proteins parvalbumin (PV) and calretinin (CR) has not yet been properly assessed. Using quantitative stereologic methods, we analyzed the regional pattern of age-related loss of PV- and CR-immunoreactive (ir) neurons in the hippocampus of mice that carry M233T/L235P knocked-in mutations in presenilin-1 (PS1) and overexpress a mutated human beta-amyloid precursor protein (APP), namely, the APP(SL)/PS1 KI mice, as well as in APP(SL) mice and PS1 KI mice. We found a loss of PV-ir neurons (40-50%) in the CA1-2, and a loss of CR-ir neurons (37-52%) in the dentate gyrus and hilus of APP(SL)/PS1 KI mice. Interestingly, comparable PV- and CR-ir neuron losses were observed in the dentate gyrus of postmortem brain specimens obtained from patients with AD. The loss of these interneurons in AD may have substantial functional repercussions on local inhibitory processes in the hippocampus.

GABA(A) receptor-mediated acceleration of aging-associated memory decline in APP/PS1 mice and its pharmacological treatment by picrotoxin

Advanced age and mutations in the genes encoding amyloid precursor protein (APP) and presenilin (PS1) are two serious risk factors for Alzheimer's disease (AD). Finding common pathogenic changes originating from these risks may lead to a new therapeutic strategy. We observed a decline in memory performance and reduction in hippocampal long-term potentiation (LTP) in both mature adult (9-15 months) transgenic APP/PS1 mice and old (19-25 months) non-transgenic (nonTg) mice. By contrast, in the presence of bicuculline, a GABA(A) receptor antagonist, LTP in adult APP/PS1 mice and old nonTg mice was larger than that in adult nonTg mice. The increased LTP levels in bicuculline-treated slices suggested that GABA(A) receptor-mediated inhibition in adult APP/PS1 and old nonTg mice was upregulated. Assuming that enhanced inhibition of LTP mediates memory decline in APP/PS1 mice, we rescued memory deficits in adult APP/PS1 mice by treating them with another GABA(A) receptor antagonist, picrotoxin (PTX), at a non-epileptic dose for 10 days. Among the saline vehicle-treated groups, substantially higher levels of synaptic proteins such as GABA(A) receptor alpha1 subunit, PSD95, and NR2B were observed in APP/PS1 mice than in nonTg control mice. This difference was insignificant among PTX-treated groups, suggesting that memory decline in APP/PS1 mice may result from changes in synaptic protein levels through homeostatic mechanisms. Several independent studies reported previously in aged rodents both an increased level of GABA(A) receptor alpha1 subunit and improvement of cognitive functions by long term GABA(A) receptor antagonist treatment. Therefore, reduced LTP linked to enhanced GABA(A) receptor-mediated inhibition may be triggered by aging and may be accelerated by familial AD-linked gene products like Abeta and mutant PS1, leading to cognitive decline that is pharmacologically treatable at least at this stage of disease progression in mice.