Genetic evidence predicts a causative role for amyloid-␤ (A␤) in Alzheimer's disease. Recent debate has focused on whether fibrils (amyloid) or soluble oligomers of A␤ are the active species that contribute to neurodegeneration and dementia. We developed two aggregation protocols for the consistent production of stable oligomeric or fibrillar preparations of A␤-(1-42). Here we report that oligomers inhibit neuronal viability 10-fold more than fibrils and ϳ40-fold more than unaggregated peptide, with oligomeric A␤-(1-42)-induced inhibition significant at 10 nM. Under A␤-(1-42) oligomer-and fibril-forming conditions, A␤-(1-40) remains predominantly as unassembled monomer and had significantly less effect on neuronal viability than preparations of A␤-(1-42). We applied the aggregation protocols developed for wild type A␤-(1-42) to A␤-(1-42) with the Dutch (E22Q) or Arctic (E22G) mutations. Oligomeric preparations of the mutations exhibited extensive protofibril and fibril formation, respectively, but were not consistently different from wild type A␤-(1-42) in terms of inhibition of neuronal viability. However, fibrillar preparations of the mutants appeared larger and induced significantly more inhibition of neuronal viability than wild type A␤-(1-42) fibril preparations. These data demonstrate that protocols developed to produce oligomeric and fibrillar A␤-(1-42) are useful in distinguishing the structural and functional differences between A␤-(1-42) and A␤-(1-40) and genetic mutations of A␤-(1-42). Amyloid-␤ (A␤)1 is derived by the proteolytic processing of amyloid precursor protein (APP), resulting in a peptide predominantly 40 or 42 amino acids in length. Mutations in APP and the presenilins that increase the amount of A␤-(1-42) cause AD (for review, see Ref. 1). Historically, the "amyloid cascade" hypothesis has defined the fibrillization of A␤ into amyloid deposits, a pathologic hallmark of AD, as a toxic gain of function (2). That A␤-(1-42) is more fibrillogenic than A␤-(1-40) fits well with this hypothesis. However, amyloid plaques do not always correlate in number, tempo, or distribution with neurodegeneration or clinical dementia. Thus, recent debate within the AD community has focused on whether fibrillar (amyloid) or soluble oligomers of A␤ are the active species of the peptide that ultimately cause the synaptic loss and dementia associated with AD (3-7). In vivo, small, stable oligomers of A␤-(1-42) have been isolated from brain, plasma, and cerebrospinal fluid (8 -10) and correlate with the severity of neurodegeneration in AD (11, 12). Thus, although genetic evidence predicts that A␤ is a causative factor in AD, the role of fibrillar and oligomeric A␤ in the pathogenesis of AD remains unclear.Initial in vitro studies suggested that A␤-induced neurotoxicity required the peptide to adopt a fibrillar aggregation state, with unaggregated peptide at low doses actually exhibiting neurotrophic effects (13)(14)(15)(16)(17)(18)). Recent studies demonstrate that non-fibrillar structures, including oligomers and ...

Angelman syndrome (AS) is a severe neurodevelopmental disorder associated with disruption of maternally inherited UBE3A (ubiquitin protein ligase E3A) expression. At the present time, there is no effective treatment for AS. Mouse lines with loss of maternal Ube3a (Ube3am–/p+) recapitulate multiple aspects of the clinical AS profile, including impaired motor coordination, learning deficits, and seizures. Thus, these genetic mouse models could serve as behavioral screens for preclinical efficacy testing, a critical component of drug discovery for AS intervention. However, the severity and consistency of abnormal phenotypes reported in Ube3am–/p+ mice can vary, dependent upon age and background strain, which is problematic for the detection of beneficial drug effects. As part of an ongoing AS drug discovery initiative, we characterized Ube3am–/p+ mice on either a 129S7/SvEvBrd-Hprtb-m2 (129) or C57BL/6J (B6) background across a range of functional domains and ages to identify reproducible and sufficiently large phenotypes suitable for screening therapeutic compounds. The results from the study showed that Ube3am–/p+ mice have significant deficits in acquisition and reversal learning in the Morris water maze. The findings also demonstrated that Ube3am–/p+ mice exhibit motor impairment in a rotarod task, hypoactivity, reduced rearing and marble-burying, and deficient fear conditioning. Overall, these profiles of abnormal phenotypes can provide behavioral targets for evaluating effects of novel therapeutic strategies relevant to AS.

Treatment of attention deficit hyperactivity disorder with the psychostimulant drug methylphenidate (MP) has increased dramatically among schoolchildren. We tested whether repeated exposure to moderate doses of MP (5 and 10 mg/kg IP for 5 or 7 days) in adolescent rats increased reactivity to cocaine measured by motor responses (ambulations and rearing) to a cocaine challenge in adulthood. We later tested whether repeated exposure to a low dose of MP (2 mg/kg IP for 7 days) enhanced the psychomotor effects of cocaine, measured by different challenge doses (0-30 mg/kg) as well as to the reinforcing effects of cocaine, measured by self-administration of lowdose infusion (75 g/kg, IV). We found that exposure to moderate doses of MP enhanced psychomotor responses to cocaine but exposure to a low dose only increased cocaine self-administration. These results suggest that adolescent exposure to low doses of MP in rats mayMethylphenidate (Ritalin ® ) is used widely in the treatment of attention deficit hyperactivity disorder (ADHD), the most commonly diagnosed disorder of childhood (Swanson et al. 1998). During the 1990s, diagnosis and treatment of this disorder grew dramatically in the United States. Estimates show that up to 15% of school age children may be affected in certain geographical locations (Scahill and Schwab-Stone 2000) and that prevalence is estimated to be 5-10% in the general population (Swanson et al. 1998). In addition, preschoolers (Zito et al. 2000) and children who do not meet the diagnostic criteria for ADHD (Marshall 2000) have recently been identified as two new groups increasingly exposed to this drug. The duration of treatment is several years in childhood, more often extending into adolescence and adulthood (Garland 1998;Robin 1999;Silver 2000;Spencer et al. 2000).Animal studies have shown that MP is a psychostimulant, which, as with cocaine, blocks the dopamine transporter (DAT) (Kuczenski and Segal 1997); thereby increasing extracellular dopamine (DA) levels in the striatum and nucleus accumbens (Kuczenski 1983), brain regions involved in the locomotor and reinforcing effects of psychostimulants and other drugs of abuse (Koob and Bloom 1988 NO . 5 et al. 1999). Oral therapeutic doses of MP effectively block more than 50% of DATs (Volkow et al. 1998); thereby increasing extracellular DA levels (Volkow et al. 2001). These actions are highly associated with the reinforcing properties of drugs (Ritz et al. 1987). Taken together, the well-documented abuse potential of psychostimulants (for reviews see White and Wolf 1991;Robinson and Berridge 1993;Self and Nestler 1995), studies linking ADHD with subsequent substance abuse (Wilens et al. 1997;Clure et al. 1999;Schubiner et al. 2000), and the dearth of controlled studies on the effects of long-term stimulant exposure on the brain, all make MP exposure an important public health issue.Animal models of drug addiction clearly indicate that repeated exposure to psychostimulants results in augmented behaviors (sensitization) that can be detected lo...

These results show that inhibiting dopamine cell impulse activity, by activation of dopamine autoreceptors, reduces drug-seeking behavior. This suggests that the impulse activity of midbrain dopamine cells could be an important factor contributing to relapse.