Yin‐Guo Lin

The mechanisms by which neurons and synapses are lost in Alzheimer's disease (AD) are not completely understood. To characterize potential signaling events linked to AD pathogenesis, activation-specific antibodies were used to examine mitogen-activated protein kinase (MAPK) kinase pathways at various ages in mice transgenic for human amyloid precursor protein-695 with the Swedish familial AD mutations (Tg2576) and homozygous for a P264L familial AD mutation introduced by targeting of the presenilin-1 gene (PS1(P264L)). Although the c-Jun N-terminal kinase (JNK) and p38 pathways were significantly activated in the cortex at both 7 and 12 months of age, there was no significant activation of the extracellular signal-regulated kinase pathway. MAPK kinase-4, an upstream activator of JNK, was also significantly activated at 7 and 12 months, whereas c-Jun, a downstream effector of JNK-associated apoptotic signaling, was not induced. The lack of c-Jun activation is consistent with the absence of neuronal loss in both cortex and hippocampal CA1 at 12 months. The JNK activation was localized to amyloid deposits, within neurites containing phosphorylated tau. Synaptophysin was quantified biochemically as a measure of synaptic integrity and was significantly reduced in an age-dependent manner in the Tg2576/PS1(P264L) cortex but not in either PS1(P264L) or Tg2576 cortex. Stress-responsive MAP kinase pathways were activated in the brain of the Tg2576/PS1(P264L) AD model, and this activation was coincident with the age-dependent increase in amyloid deposition, tau phosphorylation, and loss of synaptophysin.

The pathogenic mechanism linking presenilin-1 (PS-1) gene mutations to familial Alzheimer's disease (FAD) is uncertain, but has been proposed to include increased neuronal sensitivity to degeneration and enhanced amyloidogenic processing of the beta-amyloid precursor protein (APP). We investigated this issue by using gene targeting with the Cre-lox system to introduce an FAD-linked P264L mutation into the endogenous mouse PS-1 gene, an approach that maintains normal regulatory controls over expression. Primary cortical neurons derived from PS-1 homozygous mutant knock-in mice exhibit basal neurodegeneration similar to their PS-1 wild-type counterparts. Staurosporine and Abeta1-42 induce apoptosis, and neither the dose dependence nor maximal extent of cell death is altered by the PS-1 knock-in mutation. Similarly, glutamate-induced neuronal necrosis is unaffected by the PS-1P264L mutation. The lack of effect of the PS-1P264L mutation is confirmed by measures of basal- and toxin-induced caspase and calpain activation, biochemical indices of apoptotic and necrotic signaling, respectively. To analyze the influence of the PS-1P264L knock-in mutation on APP processing and the development of AD-type neuropathology, we created mouse lines carrying mutations in both PS-1 and APP. In contrast to the lack of effect on neuronal vulnerability, cortical neurons cultured from PS-1P264L homozygous mutant mice secrete Abeta42 at an increased rate, whereas secretion of Abeta40 is reduced. Moreover, the PS-1 knock-in mutation selectively increases Abeta42 levels in the mouse brain and accelerates the onset of amyloid deposition and its attendant reactive gliosis, even as a single mutant allele. We conclude that expression of an FAD-linked mutant PS-1 at normal levels does not generally increase cortical neuronal sensitivity to degeneration. Instead, enhanced amyloidogenic processing of APP likely is critical to the pathogenesis of PS-1-linked FAD.

STUDY OBJECTIVE: Rebound hypersomnolence (RHS: increased sleep following increased wake) is a limiting side-effect of many wake-promoting agents. In particular, RHS in the first few hours following wake appears to be associated with dopamine (DA)-releasing agents, e.g., amphetamine, but whether it can also be produced by DA transporter (DAT) inhibition alone is unknown. In these studies, DA-releasing and DAT-inhibiting agents and their interaction were systematically examined for their ability to increase wake and induce RHS. DESIGN: Chronically implanted rats were evaluated in a blinded, pseudo-randomized design. PARTICIPANTS: 237 rats were used in these studies with 1 week between repeat tests. INTERVENTIONS: Animals were habituated overnight and dosed the next day, 5 h after lights on, with test agents. MEASUREMENTS AND RESULTS: Sleep/wake activityand RHS were evaluated using EEG/EMG recording up to 22 h post dosing. In vitro dopamine release was evaluated in rat synaptosomes. At doses that produced equal increases in wake, DA-releasing (amphetamine, methamphetamine, phentermine) and several DAT-inhibiting agents (cocaine, bupropion, and methylphenidate) produced RHS during the first few hours after the onset of sleep recovery. However, other DAT-inhibiting agents (mazindol, nomifensine, GBR-12909, and GBR-12935) did not produce RHS. Combination treatment with amphetamine and nomifensine produced waking activity greater than the sum of their individual activities alone while ameliorating the amphetamine-like RHS. In rat synaptosomes, nomifensine reduced the potency of amphetamine to induce DA release approximately 270-fold, potentially explaining its action in ameliorating amphetamine-induced RHS. CONCLUSIONS: All DA releasing agents tested, and some DAT-inhibiting agents, produced RHS at equal wake-promoting doses. Thus amphetamine-like DA release appears sufficient for inducing RHS, but additional properties (pharmacologic and/or pharmacokinetic) evidently underlie RHS of other DAT inhibitors. Enhancing wake while mitigating RHS can be achieved by combining DAT-inhibiting and DA-releasing agents.