Conditioned inhibition of amphetamine sensitization.

Repeated intermittent exposure to psychostimulants, such as amphetamine, leads to a progressive enhancement of the drug's ability to increase both behavioral and brain neurochemical responses. The expression of these enhancements, known as sensitization, can be regulated by Pavlovian conditioned stimuli. Cues that are associated with drug experience can facilitate sensitization so that it only occurs in the presence of these stimuli (context-specific sensitization). In contrast, cues that are explicitly related to the absence of drugs (conditioned inhibitors) can prevent the expression of sensitization. We hypothesized that disrupting conditioned inhibition would enable amphetamine sensitization in new contexts. Using male Sprague Dawley rats and a two-context amphetamine conditioning procedure, we found that extinguishing amphetamine experience in one environment led to the loss of conditioned inhibition in a separate context. Thus, amphetamine-induced sensitized locomotion, as well as both enhanced dopamine and glutamate neurotransmission in the nucleus accumbens, were observed in a context where the drug was never experienced before. A similar loss of contextual control of sensitization was seen after using baclofen/muscimol microinjections to transiently inhibit the medial prefrontal cortex, basolateral amygdala, or ventral subiculum of the hippocampus. In other words, compared to control infusions, these intracranial injections of GABA-receptor agonists were able to block conditioned inhibitors from preventing the expression of sensitized locomotion. Together, these findings reveal the importance of conditioned inhibitors for regulating addiction-like behavior. The results suggest that dopaminergic and glutamatergic brain circuitry controls the context-specific expression of amphetamine sensitization.

The Overall Poor Specificity of MRCP in the Preoperative Evaluation of the Jaundiced Patient Will Increase the Incidence of Nontherapeutic ERCP.

Laparoscopic cholecystectomy remains one of the most common surgical operations. Common bile duct stones (CBDS) are estimated to be present in 10%-20% of individuals with symptomatic gallstones. Preoperative magnetic resonance cholangiopancreatography (MRCP) and intraoperative cholangiography (IOC) remain the most common methods of evaluation, with subsequent endoscopic retrograde cholangiopancreatography (ERCP) for stone extraction if positive for CBDS. We examined our experience with preoperative MRCP versus IOC for the management of the jaundiced patient with cholelithiasis. This is a retrospective single-institution study that examined all laparoscopic cholecystectomies performed over a 15-month period between 2017 and 2018. Outpatient elective cases were excluded from the analysis. Charts were reviewed for demographics, operative details, and whether an MRCP, IOC, or ERCP was performed. Data were evaluated using a 2-sample t-test. A total of 460 patients underwent laparoscopic cholecystectomy over a 15-month period. Of those, 147 underwent either an MRCP or an IOC for clinical suspicion for CBDS. ERCP after MRCP was nontherapeutic in 11/32 (34%) compared with 2/12 (17%) of patients following IOC. The sensitivity and specificity of MRCP were 91% and 80%, respectively, with a positive predictive value of 66% and a negative predictive value of 96%. The sensitivity and specificity of IOC were 83% and 97%, respectively, with a positive predictive value of 83% and a negative predictive value of 97%. MRCP and IOC have unique advantages and disadvantages. MRCP has greater sensitivity, but poor specificity, resulting in unnecessary ERCPs with associated morbidity and increased costs to the patient.

Preaxial polydactyly following early gestational exposure to the smoothened agonist, SAG, in C57BL/6J mice.

BACKGROUND: While pharmacological activation of the Hedgehog (HH) signaling pathway may have therapeutic benefits for developmental and adult diseases, its teratogenic potential is of concern. The membrane molecule Smoothened (SMO) transduces HH signaling and can be acutely modulated by antagonists and agonists. The objective of the current experiments was to determine how maternal treatment with the Smo agonist, SAG, affects the developing limb. METHODS: Pregnant C57BL/6J mice received a single injection of SAG (15, 17, or 20 mg/kg, i.p.) or its vehicle on gestational day (GD) 9.25, the time of limb bud induction. Embryos were examined on GD 15 for gross dysmorphology and skeletal staining was performed to visualize the number and type of digits on the fore- and hindlimbs. Additionally, in situ hybridization was performed 4 hr after GD 9.25 SAG administration to determine SAG's effects on Gli1 and Gli2 mRNA expression. RESULTS: The most prevalent effect of SAG was the dose-dependent induction of pre-axial polydactyly; defects ranged from a broad thumb to the duplication of two finger-like digits on the preaxial side of the thumb. The highest SAG dose was effective in ca. 80% of the embryos and increased Gli1 and Gli2 mRNA expression in the limb bud, with Gli1 mRNA being the most upregulated. CONCLUSION: Preaxial polydactyly can be caused in the developing embryo by acute maternal administration of a Smo agonist that activates HH signaling. These results are consistent with the preaxial polydactyly induced in developmental disorders associated with mutations in HH signaling genes.Birth Defects Research 109:49-54, 2017. © 2016 Wiley Periodicals, Inc.

Reversal of social deficits by subchronic oxytocin in two autism mouse models.

Social deficits are a hallmark feature of autism spectrum disorder (ASD) and related developmental syndromes. Although there is no standard treatment for social dysfunction, clinical studies have identified oxytocin as a potential therapeutic with prosocial efficacy. We have previously reported that peripheral oxytocin treatment can increase sociability and ameliorate repetitive stereotypy in adolescent mice from the C58/J model of ASD-like behavior. In the present study, we determined that prosocial oxytocin effects were not limited to the adolescent period, since C58/J mice, tested in adulthood, demonstrated significant social preference up to 2 weeks following subchronic oxytocin treatment. Oxytocin was also evaluated in adult mice with underexpression of the N-methyl-d-aspartate receptor NR1 subunit (encoded by Grin1), a genetic model of autism- and schizophrenia-like behavior. Subchronic oxytocin had striking prosocial efficacy in male Grin1 knockdown mice; in contrast, chronic regimens with clozapine (66 mg/kg/day) or risperidone (2 mg/kg/day) failed to reverse deficits in sociability. Neither the subchronic oxytocin regimen, nor chronic treatment with clozapine or risperidone, reversed impaired prepulse inhibition in the Grin1 knockdown mice. Overall, these studies demonstrate oxytocin can enhance sociability in mouse models with divergent genotypes and behavioral profiles, adding to the evidence that this neurohormone could have therapeutic prosocial efficacy across a spectrum of developmental disorders.

Dose-dependent teratogenicity of the synthetic cannabinoid CP-55,940 in mice.

Potent synthetic cannabinoids (SCBs) are illegally distributed drugs of abuse that are frequently consumed in spite of their adverse consequences. This study was designed to determine if the toxicity observed in adults also extends to the prenatal period by examining the developmental toxicity/teratogenicity of one of these SCBs, CP-55,940, in a mammalian model. First, immunohistochemistry was employed for cannabinoid receptor 1 (CB1) localization within gestational day (GD) 8 mouse embryos; this receptor was identified in the cranial neural plate, suggesting that the endogenous cannabinoid system may be involved in normal development. Based on this information and on previous avian teratogenicity studies, the current investigation focused on cannabinoid exposure during neurulation. The treatment paradigm involved acute i.p. administration of vehicle, 0.0625, 0.125, 0.25, 0.5, 1.0, or 2.0mg/kg CP-55,940 to time-mated C57Bl/6J mice on their 8th day of pregnancy (n>10 litters per treatment group). On GD 17, litters were harvested and examined for numbers of live, dead, or resorbed fetuses, as well as for fetal weight, length, and gross morphological abnormalities. No effect on litter size, fetal weight, or crown rump length was seen at any of the CP-55,940 dosages tested. Major malformations involving the craniofacies and/or eyes were noted in all drug-treated groups. Selected fetuses with craniofacial malformations were histologically sectioned and stained, allowing investigation of brain anomalies. Observed craniofacial, ocular, and brain abnormalities in drug-treated fetuses included lateral and median facial clefts, cleft palate, microphthalmia, iridial coloboma, anophthalmia, exencephaly, holoprosencephaly, and cortical dysplasia. With the most commonly observed defects involving the eyes, the incidence and severity of readily identifiable ocular malformations were utilized as a basis for dose-response analyses. Ocular malformation ratings revealed dose-dependent CP-55,940 teratogenicity within the full range of dosages tested. While examination of additional critical periods and in depth mechanistic studies is warranted, the results of this investigation clearly show the dose-dependent teratogenicity of this SCB.

Dysmorphogenic effects of first trimester-equivalent ethanol exposure in mice: a magnetic resonance microscopy-based study.

BACKGROUND: The first trimester of human development and the equivalent developmental period in animal models is a time when teratogenic ethanol (EtOH) exposure induces the major structural birth defects that fall within fetal alcohol spectrum disorder (FASD). Previous FASD research employing an acute high dose maternal intraperitoneal EtOH treatment paradigm has identified sensitive periods for a number of these defects. Extending this work, this investigation utilized high resolution magnetic resonance microscopy (MRM)-based analyses to examine the dysmorphology resulting from maternal dietary EtOH intake occurring during selected first trimester-equivalent time periods. METHODS: Female C57Bl/6J mice were acclimated to a liquid 4.8% EtOH (v/v)-containing diet, then bred while on standard chow. Dams were again provided the EtOH-containing liquid diet for a period that extended either from the beginning of gestational day (GD) 7 to the end of GD 11 or from the beginning of GD 12 to the end of GD 16. On GD 17, a subset of fetuses was selected for MRM-based analyses. Group comparisons were made for litter characteristics and gross dysmorphology, as well as whole and regional brain volumes. RESULTS: EtOH-induced stage of exposure-dependent structural brain abnormalities were observed. The GD 7 to 11 EtOH-exposed group presented with a significant decrease in cerebellar volume and an increase in septal volume, while GD 12 to 16 EtOH treatment resulted in a reduction in right hippocampal volume accompanied by enlarged pituitaries. Additionally, the GD 12 to 16 EtOH exposure caused a high incidence of edema/fetal hydrops. CONCLUSIONS: These results illustrate the teratogenic impact of maternal dietary EtOH intake occurring at time periods approximately equivalent to weeks 3 through 6 (GD 7 to 11 in mice) and weeks 7 through 12 (GD 12 to 16 in mice) of human gestation, further documenting EtOH's stage of exposure-dependent neuroteratogenic end points and highlighting the vulnerability of selected brain regions during the first trimester. Additionally they suggest that clinical attention should be paid to fetal hydrops as a likely component of FASD.

Repetitive behavior profile and supersensitivity to amphetamine in the C58/J mouse model of autism.

Restricted repetitive behaviors are core symptoms of autism spectrum disorders (ASDs). The range of symptoms encompassed by the repetitive behavior domain includes lower-order stereotypy and self-injury, and higher-order indices of circumscribed interests and cognitive rigidity. Heterogeneity in clinical ASD profiles suggests that specific manifestations of repetitive behavior reflect differential neuropathology. The present studies utilized a set of phenotyping tasks to determine a repetitive behavior profile for the C58/J mouse strain, a model of ASD core symptoms. In an observational screen, C58/J demonstrated overt motor stereotypy, but not over-grooming, a commonly-used measure for mouse repetitive behavior. Amphetamine did not exacerbate motor stereotypy, but had enhanced stimulant effects on locomotion and rearing in C58/J, compared to C57BL/6J. Both C58/J and Grin1 knockdown mice, another model of ASD-like behavior, had marked deficits in marble-burying. In a nose poke task for higher-order repetitive behavior, C58/J had reduced holeboard exploration and preference for non-social, versus social, olfactory stimuli, but did not demonstrate cognitive rigidity following familiarization to an appetitive stimulus. Analysis of available high-density genotype data indicated specific regions of divergence between C58/J and two highly-sociable strains with common genetic lineage. Strain genome comparisons identified autism candidate genes, including Cntnap2 and Slc6a4, located within regions divergent in C58/J. However, Grin1, Nlgn1, Sapap3, and Slitrk5, genes linked to repetitive over-grooming, were not in regions of divergence. These studies suggest that specific repetitive phenotypes can be used to distinguish ASD mouse models, with implications for divergent underlying mechanisms for different repetitive behavior profiles.

Prosocial effects of oxytocin in two mouse models of autism spectrum disorders.

Clinical evidence suggests that oxytocin treatment improves social deficits and repetitive behavior in autism spectrum disorders (ASDs). However, the neuropeptide has a short plasma half-life and poor ability to penetrate the blood-brain barrier. In order to facilitate the development of more bioavailable oxytocinergic compounds as therapeutics to treat core ASD symptoms, small animal models must be validated for preclinical screens. This study examined the preclinical utility of two inbred mouse strains, BALB/cByJ and C58/J, that exhibit phenotypes relevant to core ASD symptoms. Mice from both strains were intraperitoneally administered oxytocin, using either acute or sub-chronic regimens. Acute oxytocin did not increase sociability in BALB/cByJ; however, sub-chronic oxytocin had significant prosocial effects in both BALB/cByJ and C58/J. Increased sociability was observed 24 h following the final oxytocin dose in BALB/cByJ, while prosocial effects of oxytocin emerged 1-2 weeks post-treatment in C58/J. Furthermore, acute oxytocin decreased motor stereotypy in C58/J and did not induce hypoactivity or anxiolytic-like effects in an open field test. This study demonstrates that oxytocin administration can attenuate social deficits and repetitive behavior in mouse models of ASD, dependent on dose regimen and genotype. These findings provide validation of the BALB/cByJ and C58/J models as useful platforms for screening novel drugs for intervention in ASDs and for elucidating the mechanisms contributing to the prosocial effects of oxytocin.

Behavioral deficits in an Angelman syndrome model: effects of genetic background and age.

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 (Ube3a(m-/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 Ube3a(m-/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 Ube3a(m-/p+) mice on either a 129S7/SvEvBrd-Hprt(b-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 Ube3a(m-/p+) mice have significant deficits in acquisition and reversal learning in the Morris water maze. The findings also demonstrated that Ube3a(m-/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.

Intermittent nicotine exposure upregulates nAChRs in VTA dopamine neurons and sensitises locomotor responding to the drug.

Dopaminergic projections from the ventral tegmental area (VTA) to the nucleus accumbens (NAcc) mediate the behavioral and motivational effects of many drugs of abuse, including nicotine. Repeated intermittent administration of these drugs, a pattern often associated with initial drug exposure, sensitises the reactivity of dopamine (DA) neurons in this pathway, enhances the locomotor behaviors the drugs emit, and promotes their pursuit and self-administration. Here we show that activation of nicotinic acetylcholine receptors (nAChRs) in the VTA, but not the NAcc, is essential for the induction of locomotor sensitisation by nicotine. Repeated intermittent nicotine exposure (4 × 0.4 mg/kg, base, i.p., administered over 7 days), a regimen leading to long-lasting locomotor sensitisation, also produced upregulation of nAChRs in the VTA, but not the NAcc, in the hours following the last exposure injection. Functional nAChR upregulation was observed selectively in DA but not GABA neurons in the VTA. These effects were followed by long-term potentiation of excitatory inputs to these cells and increased nicotine-evoked DA overflow in the NAcc. Withdrawal symptoms were not observed following this exposure regimen. Thus, intermittent activation and upregulation by nicotine of nAChRs in DA neurons in the VTA may contribute to the development of behavioral sensitisation and increased liability for nicotine addiction.

Disruption of social approach by MK-801, amphetamine, and fluoxetine in adolescent C57BL/6J mice.

Autism is a severe neurodevelopmental disorder, diagnosed on the basis of core behavioral symptoms. Although the mechanistic basis for the disorder is not yet known, genetic analyses have suggested a role for abnormal excitatory/inhibitory signaling systems in brain, including dysregulation of glutamatergic neurotransmission. In mice, the constitutive knockdown of NMDA receptors leads to social deficits, repetitive behavior, and self-injurious responses that reflect aspects of the autism clinical profile. However, social phenotypes differ with age: mice with reduced NMDA-receptor function exhibit hypersociability in adolescence, but markedly deficient sociability in adulthood. The present studies determined whether acute disruption of NMDA neurotransmission leads to exaggerated social approach, similar to that observed with constitutive disruption, in adolescent C57BL/6J mice. The effects of MK-801, an NMDA receptor antagonist, were compared with amphetamine, a dopamine agonist, and fluoxetine, a selective serotonin reuptake inhibitor, on performance in a three-chamber choice task. Results showed that acute treatment with MK-801 led to social approach deficits at doses without effects on entry numbers. Amphetamine also decreased social preference, but increased number of entries at every dose. Fluoxetine (10 mg/kg) had selective effects on social novelty preference. Withdrawal from a chronic ethanol regimen decreased activity, but did not attenuate sociability. Low doses of MK-801 and amphetamine were also evaluated in a marble-burying assay for repetitive behavior. MK-801, at a dose that did not disrupt sociability or alter entries, led to a profound reduction in marble-burying. Overall, these findings demonstrate that moderate alteration of NMDA, dopamine, or serotonin function can attenuate social preference in wild type mice.

Preweaning sensorimotor deficits and adolescent hypersociability in Grin1 knockdown mice.

Mice with knockdown of the N-methyl-D-aspartate (NMDA) receptor NR1 subunit, encoded by the gene Grin1, have been investigated as a model for the intrinsic NMDA hypofunction hypothesized for schizophrenia. Previous work has shown that adult Grin1 mutant mice have overt deficits in habituation and sensorimotor gating, exaggerated reactivity to environmental stimuli, reduced social approach, and other alterations that reflect behavioral manifestations of schizophrenia. In humans, the emergence of overt symptoms of the disorder typically occurs in adolescence or early adulthood, suggesting a role for aberrant maturation of NMDA receptor signaling in symptom onset. The following study evaluated Grin1 mutant mice for abnormal behavioral phenotypes during the preweaning, adolescent, and adult periods. Measures included open field activity, prepulse inhibition of acoustic startle responses, and social preference in a three-chamber choice task. Mice from the C57BL/6J inbred strain, one of the parental strains for the Grin1 line, were also tested. The results showed that developmental reduction of NMDA receptor function led to significant alterations in behavior during the second and third weeks of life, including exaggerated startle responses and sensorimotor gating deficits on postnatal day 13, and pronounced hypersociability in adolescence. Male Grin1 mutant mice were more susceptible than female mice to the detrimental effects of decreased NMDA signaling. Overall, these findings provide evidence that reduced Grin1 function leads to abnormal phenotypes in the preweaning period, and that deficient NMDA signaling can lead to both overt hypersociability or marked asociality, dependent upon sex and age.

Transient overexpression of alpha-Ca2+/calmodulin-dependent protein kinase II in the nucleus accumbens shell enhances behavioral responding to amphetamine.

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is known to contribute to the expression of psychostimulant sensitization by regulating dopamine (DA) overflow from DA neuron terminals in the nucleus accumbens (NAcc). The present experiments explored the contribution of CaMKII in NAcc neurons postsynaptic to these terminals where it is known to participate in a number of signaling pathways that regulate responding to psychostimulant drugs. Exposure to amphetamine transiently increased alphaCaMKII levels in the shell but not the core of the NAcc. Thus, HSV (herpes simplex viral) vectors were used to transiently overexpress alphaCaMKII in NAcc neurons in drug-naive rats, and behavioral responding to amphetamine was assessed. Transiently overexpressing alphaCaMKII in the NAcc shell led to long-lasting enhancement of amphetamine-induced locomotion and self-administration manifested when alphaCaMKII levels were elevated and persisting long after they had returned to baseline. Enhanced locomotion was not observed after infection in the NAcc core or sites adjacent to the NAcc. Transient elevation of NAcc shell alphaCaMKII levels also enhanced locomotor responding to NAcc AMPA and increased phosphorylation levels of GluR1 (Ser831), a CaMKII site, both soon and long after infection. Similar increases in pGluR1 (Ser831) were observed both soon and long after exposure to amphetamine. These results indicate that the transient increase in alphaCaMKII observed in neurons of the NAcc shell after viral-mediated gene transfer and likely exposure to amphetamine leads to neuroadaptations in AMPA receptor signaling in this site that may contribute to the long-lasting maintenance of behavioral and incentive sensitization by psychostimulant drugs like amphetamine.

Inhibition of CaMKII in the nucleus accumbens shell decreases enhanced amphetamine intake in sensitized rats.

Microinjection of the calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor KN-93 into the nucleus accumbens (NAcc) shell impairs expression of the sensitized locomotion and NAcc dopamine (DA) overflow normally observed in psychostimulant-exposed rats. Based on these results, we investigated the effect of NAcc shell KN-93 on the enhanced amphetamine (AMPH) intake normally observed in AMPH- relative to saline-exposed rats. Rats were administered five injections of either AMPH (1.5mg/kg, i.p.) or saline, one injection every 2-3 days. Fourteen days following the last injection, they were trained to self-administer AMPH (200 microg/kg/infusion, i.v.) first on fixed ratio schedules (FR) and then on a progressive ratio schedule of reinforcement (PR). As expected, AMPH-exposed rats worked harder and obtained significantly more drug infusions than saline-exposed rats on the PR schedule. After 4 days of stable responding, all rats were bilaterally microinjected with KN-93 (1 or 10 nmol/0.5 microl/side) into the NAcc shell, 2 min prior to the beginning of the self-administration session. Inhibiting CaMKII in this site reduced the enhanced drug intake observed in AMPH-exposed rats to levels no longer significantly different from those of saline-exposed rats. Responding in these latter controls was not affected by KN-93 nor did KN-93 affect responding in AMPH-exposed rats when it was infused into the NAcc core. Thus, in a manner similar to what has been reported for sensitized locomotion and NAcc DA overflow, these results suggest that inhibiting CaMKII in the NAcc shell attenuates the enhanced motivation to obtain a drug reinforcer that is normally displayed in AMPH-exposed rats.

Impulse activity of midbrain dopamine neurons modulates drug-seeking behavior.

RATIONALE: Withdrawal from non-contingent exposure to psychostimulants increases the activity of midbrain dopamine cells and impairs the function of impulse-regulating dopamine autoreceptors. It is unclear whether these neuroadaptations play an important role in withdrawal-associated drug seeking. OBJECTIVES: We determined whether cocaine self-administration modifies the impulse activity of midbrain dopamine neurons and dopamine autoreceptor function, and whether experimentally induced reduction in dopamine cell activity (by autoreceptor activation) could influence drug-seeking behavior. METHODS: Animals were trained to self-administer saline or cocaine (500 micro g/kg per infusion) for 7 days. At different withdrawal periods, we used single-unit extracellular recordings to measure impulse activity of dopamine cells and administered the D2/D3 dopamine receptor agonist quinpirole to determine autoreceptor sensitivity. In a separate set of experiments, we determined the effects of autoreceptor-selective doses of quinpirole on drug-seeking behavior (non-reinforced responding in the absence of cocaine) during an extinction/reinstatement task. RESULTS: Cocaine self-administration induced a short-lived increase in the mean firing rate and bursting activity of midbrain dopamine cells. This effect was greatest at early withdrawal and was paralleled by decreased ability of quinpirole to inhibit dopamine cell firing rate and drug-seeking behavior. Changes in dopamine cell activity dissipated over time; at late withdrawal, when both impulse activity and autoreceptor sensitivity returned to control values, quinpirole dramatically decreased drug-seeking behavior. CONCLUSIONS: 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.

Oligomeric and fibrillar species of amyloid-beta peptides differentially affect neuronal viability.

Genetic evidence predicts a causative role for amyloid-beta (A beta) in Alzheimer's disease. Recent debate has focused on whether fibrils (amyloid) or soluble oligomers of A beta 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 beta-(1-42). Here we report that oligomers inhibit neuronal viability 10-fold more than fibrils and approximately 40-fold more than unaggregated peptide, with oligomeric A beta-(1-42)-induced inhibition significant at 10 nm. Under A beta-(1-42) oligomer- and fibril-forming conditions, A beta-(1-40) remains predominantly as unassembled monomer and had significantly less effect on neuronal viability than preparations of A beta-(1-42). We applied the aggregation protocols developed for wild type A beta-(1-42) to A beta-(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 beta-(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 beta-(1-42) fibril preparations. These data demonstrate that protocols developed to produce oligomeric and fibrillar A beta-(1-42) are useful in distinguishing the structural and functional differences between A beta-(1-42) and A beta-(1-40) and genetic mutations of A beta-(1-42).