P1-108

Poster Presentations P1 (T2) relaxation times, a sensitive index of change in cell function. Results: Ts65Dn mice, but not Ts1Cje, exhibited significantly reduced T2 relaxation times selectively in the medial septal area, from where BFCN originate, and in brain regions normally innervated by BFCN, including hippocampus and cingulate cortex. BFCN projections to these areas, identified by choline acetyltransferase (CHAT) immunocytochemistry or acetylcholinesterase histochemistry, were selectively and markedly reduced in Ts65Dn mice and numbers of detectable BFCN in the medial septal area, identified by CHAT or p75NGFR immunolabeling, were significantly below normal. In BFCN projection areas of the cortex, dendrites in Ts65Dn brain displayed morphological changes and markedly increased levels of MAP-2, a cytoskeletal protein regulated by cholinergic innervation. Using electron microscopy and antibody markers for apoptosis pathway activation, we detected a higher than normal frequency of neurons undergoing apoptosis in affected brain regions. Conclusions: MRI revealed more widespread neuropathology in Ts65Dn mice than previously appreciated, involving postsynaptic as well as presynaptic elements of the BFCN circuit. The cholinergic deficits, MRI T2 changes, and AD-related endosomal phenotype in Ts65Dn mice, but not Ts1Cje, support growing evidence linking APP triplication to endosome dysfunction (A.Boyer-Boiteau; et al., this meeting), retrograde signaling deficits, and increased vulnerability of neurons to degeneration. P1-108

GENE EXPRESSION CHANGES AFTER MAPT EXPRESSION INHIBITION

Maciej P. Golan1,2, Jada Lewis2, Michael McKinney2, Caroline Kent2, Jennifer Gass2, Mike Heckman2, Julia Crook2, Michael L. Hutton2. 1 Medical Research Centre, Polish Academy of Sciences, Warsaw, Poland; 2Mayo Clinic, Jacksonville, FL, USA. Contact e-mail: [email protected] Background: Microtubule associated protein tau is one of the key players in multiple neurodegenerative disorders (called tauopathies), including Alzheimer’s disease. The normal function of tau is to regulate the stability of the neuronal microtubule network and it has been reported to play a direct role in axonal transport. Mutations in the MAPT gene, associated with FTDP-17, cause neurodegeneration and the associated accumulation of hyperphosphorylated aggregated tau protein. The exact cause of taurelated neurodegeneration is unclear however previous studies have implicated disturbance in microtubule function and axonal transport. At present there is no effective therapy for any of the tauopathies. Objective(s): In our experiments we examined gene expression changes in hippocampal pyramidal cells, from the CA1 region, in 9 month old inducible P301L tau trangenic mice (Tg4510). In the rTg4510 mouse, transgene suppression halts neurodegeneration and results in recovery of memory function (even after significant neuronal loss has occurred). We decided to analyze only CA1 pyramidal neurons, as they are one of the key players in memory and learning processes, and are vulnerable to early degeneration in this model of tauopathy. Methods: Gene expression changes were analyzed in laser dissected CA1 neurons by microarray both in transgenic rTg4510 mice vs non-transgenic controls and in rTg4510 mice that had been treated with doxycyclin to suppress tau P301L expression. Our goal was to identify groups of genes that are upregulated/downregulated during pathogenesis and functional recovery after transgene suppression. Results: Summarizing the microarray data in rTg4510 mice compared with control mice, we observed significant decreases in expression of multiple cell-cycle associated proteins, genes linked to calcium signalling pathways and pro-apoptotic genes. In contrast, recovery after transgene suppression was associated with increased expression of cytoskeleton and axonal transport-related genes, perhaps reflecting a mechanism to restore neuronal function. Conclusions: Our data provide key insights into the neuronal processes linked to neurodegeneration in tauopathy but more importantly suggest hypotheses as to how neuronal function recovers in this model after transgene suppression.

P1-109

S127 AGE-DEPENDENT CHANGES IN HIPPOCAMPAL GLUTAMATE LEVELS PARALLEL LEARNING IMPAIRMENT IN APP/PS1 TRANSGENIC MICE

Rimante Minkeviciene1, Jouni Ihalainen1, Tarja Malm1, N. Leguit2, J. Glennon2, Pradeep K. Banerjee3, Heikki Tanila1. 1Department of Neurobiology, A.I. Virtanen Institute, University of Kuopio, Finland, Kuopio, Finland; 2Solvay Pharmaceuticals, Weesp, Netherlands Antilles; 3 Forest Research Institute, Jersey City, NJ, USA. Contact e-mail: [email protected] Background: Several lines of evidence suggest that in Alzheimer’s disease (AD), the neurotoxicity caused by ␤-amyloid (A␤) peptides may be related to elevated levels of glutamate and/or overactivity of the NMDA receptors. We have earlier shown that memantine (an NMDA receptor antagonist) improves spatial learning in APP/PS1 transgenic mice with elevated levels of A␤40 and A␤42. Objective(s): In the present study, we determined the extracellular levels of glutamate in the hippocampus of APP/PS1 mice at 6 and 16 months of age. Methods: Extracellular levels of glutamate were measured by in vivo microdialysis under basal and stimulated conditions (in the absence or presence of KCl, respectively). A separate group of 6and 16-month old APP/PS1 mice were also tested for spatial learning in the water maze, and their brain A␤ levels, amyloid plaque burden, microgliosis and astrogliosis were determined by ELISA and immunocytochemistry. Results: APP/PS1 mice exhibited impaired performance in the water maze at 16 months but not at 6 months. Although some plaques were present at 6 months of age, the brain levels of A␤40, A␤42 and plaque pathology increased significantly from 6 months to 16 months. The basal extracellular glutamate level in the hippocampus did not change at either age in APP/ PS1 mice, but the stimulated glutamate level was slightly higher at 6 months and significantly lower at 16 months compared to respective age-matched wild-type controls. The number of reactive microglia was elevated at 16 but not at 6 months. Conclusions: The time course of amyloid pathology and cognitive dysfunction in this APP/PS1 mouse line suggest that the observed cognitive impairment in these mice was likely associated with age-dependent increase in brain A␤ levels and degenerative changes leading to altered glutamate neurotransmission. P1-110

REELIN EXPRESSION IN PYRAMIDAL CELLS OF THE ENTORHINAL CORTEX IS DECREASED IN HUMAN AMYLOID PRECURSOR PROTEIN TRANSGENIC MICE

Jeannie Chin, Catherine Massaro, Jorge J. Palop, Nga Bien-Ly, Myo T. Thwin, Gui-Qiu Yu, Lennart Mucke. Gladstone Institute of Neurological Disease and University of California San Francisco, San Francisco, CA, USA. Contact e-mail: [email protected] Background: Reelin plays key roles in nervous system development and also modulates synaptic plasticity in the adult brain. Several lines of evidence suggest that alterations in Reelin signaling may contribute to neuronal dysfunction associated with Alzheimer’s disease (AD). Reelin signaling modulates the extent of tau phosphorylation. Cell surface receptors for Reelin, including integrins and VLDLR/ApoE2R, may be targets of amyloid-␤ (A␤), the peptide widely believed to cause AD. Signaling molecules linked to Reelin, e.g. Fyn kinase, modulate the severity of AD-related synaptic deficits in transgenic mice expressing the human amyloid precursor protein (hAPP) that gives rise to A␤. Finally, increased amounts of Reelin fragments have been found in cerebrospinal fluid from AD patients, suggesting altered processing of Reelin. Objective: We examined whether transgenic mice that express hAPP/A␤ in neurons exhibit alterations in Reelin levels in the hippocampus or entorhinal cortex, brain regions particularly vulnerable in AD. Methods: Reelin levels in different brain regions were determined by western blot analysis and the number of Reelin-expressing neurons was ascertained by immunohistochemistry and light microscopy in 6-8-month-old hAPP mice and nontransgenic controls. Results: Compared with nontransgenic controls, hAPP mice had significantly fewer Reelin-expressing pyramidal cells in the