Parkinson's disease (PD) pathology is characterized by the formation of intra-neuronal inclusions called Lewy bodies, which are comprised of alpha-synuclein (α-syn). Duplication, triplication or genetic mutations in α-syn (A53T, A30P and E46K) are linked to autosomal dominant PD; thus implicating its role in the pathogenesis of PD. In both PD patients and mouse models, there is increasing evidence that neuronal dysfunction occurs before the accumulation of protein aggregates (i.e., α-syn) and neurodegeneration. Characterization of the timing and nature of symptomatic dysfunction is important for understanding the impact of α-syn on disease progression. Furthermore, this knowledge is essential for identifying pathways and molecular targets for therapeutic intervention. To this end, we examined various functional and morphological endpoints in the transgenic mouse model expressing the human A53T α-syn variant directed by the mouse prion promoter at specific ages relating to disease progression (2, 6 and 12 months of age). Our findings indicate A53T mice develop fine, sensorimotor, and synaptic deficits before the onset of age-related gross motor and cognitive dysfunction. Results from open field and rotarod tests show A53T mice develop age-dependent changes in locomotor activity and reduced anxiety-like behavior. Additionally, digigait analysis shows these mice develop an abnormal gait by 12 months of age. A53T mice also exhibit spatial memory deficits at 6 and 12 months, as demonstrated by Y-maze performance. In contrast to gross motor and cognitive changes, A53T mice display significant impairments in fine- and sensorimotor tasks such as grooming, nest building and acoustic startle as early as 1-2 months of age. These mice also show significant abnormalities in basal synaptic transmission, paired-pulse facilitation and long-term depression (LTD). Combined, these data indicate the A53T model exhibits early- and late-onset behavioral and synaptic impairments similar to PD patients and may provide useful endpoints for assessing novel therapeutic interventions for PD.

Recent studies have demonstrated that soluble Aβ dimers isolated from AD brains inhibit long-term potentiation (LTP), reduce dendritic spine density in vitro and upon direct injection into the brain of normal rats disrupt memory (Shankar et al., 2008). In the current study we evaluated the acquisition performance of PSAPP mice in a Morris water maze, and searched for Aβ oligomers in brains of PSAPP transgenic mice to determine whether the soluble Aβ in the transgenic mice has similar biochemical properties to human Aβ extracted from AD brains. Wild type (wt) and heterozygous PSAPP mice were trained in the Morris water maze (4 trials/day for 9 days) and the latency to reach the platform was recorded for each trial. Soluble Aβ oligomers were measured from the brains of the PSAPP transgenic mice using a sensitive immunoprecipitation/Western blotting protocol after homogenizing the whole cerebra in Tris-buffered saline. Aged mice (>12 months) exhibit an increase in plaque load and have deficits in the Morris water maze. We observe high levels of Aβ dimers in young transgenic mice (2-3 months of age) which decline before increasing again from 7-12 months. No overt cognitive deficits were seen in the 3 and 9 month old mice suggesting that dimers need to reach a critical threshold before memory deficits, in this specific cognitive paradigm, are observed. Both Aβ1-40 and Aβ1-42 are present in soluble extracts from PSAPP brains. However, in human AD brains Aβ1-42 is the predominant species in the soluble extract. These studies demonstrate that the biochemical and, potentially, the pathophysiological properties of Aβ in young PSAPP mice are different from that of Aβ extracted from elderly human AD patients.

The 5-HT6 receptor (5-HT6R) is a G-protein coupled receptor positively coupled to adenylate cyclase primarily localized within the central nervous system, particularly in brain regions associated with cognition. Antagonism of the 5-HT6R has been reported to modulate the release of multiple neurotransmitters including elevating extracellular levels of glutamate and acetylcholine in regions associated with cognitive function such as the cerebral cortex and hippocampal formation. Accumulating preclinical and clinical data suggest that 5-HT6R antagonists may function to improve cognitive performance and therefore serve as effective treatment options for Alzheimer's disease. SAM-531 (WAY-262531) is a new chemical entity that is a selective full antagonist at the 5-HT6R. Here we describe the pre-clinical profile of SAM-531 in support of its clinical development as a treatment for Alzheimer's disease. SAM-531 was characterized in vitro in multiple assays evaluating binding affinity, functional activity and receptor selectivity. In vivo characterization of SAM-531 consisted of an evaluation of the effect of treatment on brain neurochemistry using in vivo microdialysis as well as tests of rodent cognitive function such as contextual fear conditioning and novel object recognition. Cognitive testing was performed in assays utilizing both pharmacological and non-pharmacological deficit states. SAM-531 is a potent and selective full antagonist at the human 5-HT6R (Ki = 1.0 nM; IC50 = 10 nM). In rats, oral administration of SAM-531 caused significant increases in extracellular levels of glutamate and acetylcholine in the dorsal hippocampus. Treatment with SAM-531 blocked a scopolamine-induced deficit in a hippocampal-dependent learning and memory task, contextual fear conditioning. In addition, SAM-531 treatment blocked both glutmatergic- (MK-801) and cholinergic-mediated (scopolamine) deficits in recognition memory. Furthermore, treatment with SAM-531 enhanced retention of recognition memory when measured 48 hours after training, a time at which memory no longer can be measured in vehicle-treated animals. SAM-531 is a potent, selective and orally bioavailable 5-HT6R antagonist which modulates neurotransmitters associated with learning and memory and is active in multiple assays of cognitive dysfunction in the rodent. These studies provide pre-clinical support for the further development of the 5-HT6R antagonist SAM-531 as a potential treatment for Alzheimer's disease.

One of the defining hallmarks of Alzheimer's disease (AD) is the presence of extracellular plaques composed of the neurotoxic peptide beta-amyloid (Aβ). The Aβ peptide is generated by endoproteolysis of the amyloid precursor protein (APP) and alterations in this process can lead to Aβ overproduction and aggregation. In recent years the mechanisms by which APP is processed to generate Aβ have been well established and pharmaceuticals aimed at reducing Aβ are currently being tested in the clinic. Despite this however, the physiological relevance of APP processing still remains elusive. To gain a better understanding of APP functionality we chose to examine the transcriptional changes associated with over-expression of the Swedish Familial AD mutant of APP (APPswe) in the Tg2576 mouse model of AD. Using transcriptional profiling analysis, we examined gene expression differences in regions of the brain most severely affected by the disease, namely the hippocampus, amygdala and entorhinal cortex. Remarkably, in all three brain regions the most robust differences in mRNA expression appeared in genes linked to cholesterol regulation and homeostasis. In all cases expression levels of cholesterol-related genes were significantly increased in the transgenic animals compared to wild-type littermates. These microarray results have now been confirmed in five independent cohorts of animals using Taqman quantitative RT-PCR. Further analysis of selected genes has demonstrated consistent up-regulation of cholesterol genes across a range of ages from 9 and 20 weeks. Furthermore, results suggest that acutely treating 20-week-old mice with compounds that inhibit APP processing can correct this cholesterol phenotype. We are currently investigating whether these effects at the transcriptional level are translated into differences in protein expression and, moreover, what impact these changes have on cholesterol dynamics in the transgenic animals. Although the precise mechanisms involved are yet to be established, these data suggest a role for APP and APP processing in the regulation of cholesterol homeostasis, further implicating dysregulation of cholesterol in the etiology of Alzheimer's disease.

Previous investigations have shown that rats bury a variety of conditioned and unconditioned aversive stimuli. Such burying has been considered as a species‐typical defensive reaction. In the present studies, rats buried spouts filled with Tabasco sauce, or condensed milk to which a taste aversion was conditioned, but did not bury water‐filled spouts or spouts filled with a palatable novel food (apple juice) to which a taste aversion was not conditioned. However, in other experiments rats consistently and repeatedly buried Purina Rat Chow, Purina Rat Chow coated with quinine, and glass marbles. This indicates that a variety of stimuli, not all aversive or novel, evoke burying by rats. Whereas the behavior may reasonably be considered as a species‐typical defensive behavior in some situations, the wide range of conditions that occasion burying suggests that the behavior has no single biological function.

During 1974-1978, over 40% of the nonhuman drug studies that appeared in Psychopharmacology, Pharmacology Biochemistry and Behavior, and Journal of Pharmacology and Experimental Therapeutics involved human observers; far fewer studies published in Journal of the Experimental Analysis of Behavior did so. In all of these journals, measures of interobserver agreement seldom were provided. The great majority of studies also failed to utilize one or more "blind" observers, unaware of experimental conditions. These findings are of interest in light of reports that observational data are affected by a wide range of factors and often provide an inaccurate index of behavior. The believability of observational data seemingly is enhanced by careful descriptions of recording procedures coupled with the use of two or more blind observers whose concordance in rating behavior has been determined. These procedures characteristically are followed in some behavioral sciences, such as applied behavior analysis, but not to the same degree in psychopharmacology.