A comparative neuropsychological test battery differentiates cognitive signatures of Fragile X and Down syndrome.

BACKGROUND: Standardised neuropsychological and cognitive measures present some limitations in their applicability and generalisability to individuals with intellectual disability (ID). Alternative approaches to defining the cognitive signatures of various forms of ID are needed to advance our understanding of the profiles of strengths and weaknesses as well as the affected brain areas. AIM: To evaluate the utility and feasibility of six non-verbal comparative neuropsychological (CN) tasks administered in a modified version of the Wisconsin General Test Apparatus (WGTA) to confirm and extend our knowledge of unique cognitive signatures of Fragile X syndrome (FXS) and Down syndrome (DS). METHOD: A test battery of CN tasks adapted from the animal literature was administered in a modified WGTA. Tasks were selected that have established or emerging brain-behaviour relationships in the domains of visual-perceptual, visual-spatial, working memory and inhibition. RESULTS: Despite the fact that these tasks revealed cognitive signatures for the two ID groups, only some hypotheses were supported. Results suggest that whereas individuals with DS were relatively impaired on visual-perceptual and visual-spatial reversal learning tasks they showed strengths in egocentric spatial learning and object discrimination tasks. Individuals with FXS were relatively impaired on object discrimination learning and reversal tasks, which was attributable to side preferences. In contrast, these same individuals exhibited strengths in egocentric spatial learning and reversal tasks as well as on an object recognition memory task. Both ID groups demonstrated relatively poor performance for a visual-spatial working memory task. CONCLUSION: Performance on the modified WGTA tasks differentiated cognitive signatures between two of the most common forms of ID. Results are discussed in the context of the literature on the cognitive and neurobiological features of FXS and DS.

Acetyl-L-carnitine and alpha-lipoic acid supplementation of aged beagle dogs improves learning in two landmark discrimination tests.

Beagle dogs between 7.6 and 8.8 years of age administered a twice daily supplement of alpha-lipoic acid (LA) and acetyl-L-carnitine (ALC) over approximately 2 months made significantly fewer errors in reaching the learning criterion on two landmark discrimination tasks compared to controls administered a methylcellulose placebo. Testing started after a 5 day wash-in. The dogs were also tested on a variable delay version of a previously acquired spatial memory task; results were not significant. The improved performance on the landmark task of dogs supplemented with LA + ALC provides evidence of the effectiveness of this supplement in improving discrimination and allocentric spatial learning. We suggest that long-term maintenance on LA and ALC may be effective in attenuating age-associated cognitive decline by slowing the rate of mitochondrial decay and cellular aging.

MRI measurement of the canine auditory pathways and relationship with brainstem auditory evoked responses.

The objective of this study was to determine direct measurements of auditory pathways by magnetic resonance imaging (MRI) during the growth period of healthy Beagles, and to discover how canine brainstem auditory evoked response (BAER) latencies vary in relation to these MRI measurements. Eighty healthy Beagles were tested at eight, 16 and 52 weeks of age (stages 1, 2, 3, respectively) with BAER and brain MRI. The BAER interpeak latency (IPL) II-V and brain MRI neural generators of BAER waves II and V were identified. A linear distance was calculated in millimeters in order to determine the approximate length of auditory pathways. Sensory nerve conduction velocity (SNCV) of the auditory pathway between peak II and peak V was calculated for each group. A significant difference was observed between brain MRI distances among the three stages. Mean BAER IPL II-V were not significantly different between the three stages. The progressive growth of the skull and brain witnessed by the progressive increased distance of the MRI auditory pathways between peak II and peak V was not associated with a progressive maturation of the BAER IPL II-V. The SNCV of the auditory pathway between peak II and peak V was 6.14 m/sec for group 1; 6.76 m/sec for group 2; and 7.32 m/sec for group 3.

The oil-rich alga Schizochytrium sp. as a dietary source of docosahexaenoic acid improves shape discrimination learning associated with visual processing in a canine model of senescence.

Whole cell Schizochytrium sp. is a rich source of omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) including docosahexaenoic acid (DHA), an important nutrient for brain health. Aged beagle dogs experienced on a visuospatial task of working memory, variable-delay delayed-non-matching-to-position were used to assess efficacy of DHA-rich microalgae based upon DHA wt% of total phospholipids and 8-iso-PGF2α concentrations in plasma, and performance on cognitive assessments of visual object discrimination, learning, and memory consolidation after 25 weeks on fortified diet. Improved DHA status (p<0.001) and initial learning of the protocols for visual and variable contrast discrimination (p<0.05), but not long-term recall of the concurrent discrimination task were observed in animals fed the algal-fortified diet. Overall, results were consistent with dried Schizochytrium sp. as a source of n-3 LCPUFA nutrition to support DHA status in large mammals, and healthy brain function in a canine model of senescence.

Effects of dietary supplementation with a mixed blueberry and grape extract on working memory in aged beagle dogs.

Cellular oxidative damage is thought to be one of the key mechanisms underlying age-related cognitive impairment in dogs. Several nutritional interventions to limit cognitive decline are reported in the literature. To our knowledge, the association of grape and blueberry extracts has never been tested in aged dogs. Our objective was to evaluate the effect of a polyphenol-rich extract from grape and blueberry (PEGB) on oxidative status and cognitive performances in aged dogs. A total of thirty-five beagle dogs (aged 8·0-14·5 years) were fed a basal diet with PEGB at either 0 parts per million (ppm) (n 11; control), 240 ppm (n 12; PEGB1) or 480 ppm (n 12; PEGB2) for 75 d. To investigate the effects of PEGB supplementation on cognition and oxidative status, a delayed non-matching to position (DNMP) test and RT-PCR on genes involved in oxidative stress were evaluated. The dogs fed PEGB1 showed a higher superoxide dismutase mRNA expression compared with dogs fed PEGB2 (P = 0·042) and with the control group (P = 0·014). Moreover, the dogs fed PEGB2 showed higher nuclear factor-like 2 (Nrf2) mRNA expression compared with the dogs fed PEGB1 (P = 0·027). Concerning the DNMP test, the proportion of dogs showing cognitive improvements relative to their baseline level was significantly higher in dogs fed the PEGB, regardless of the dosage, than in dogs receiving no supplementation (P = 0·030). The results obtained in the DNMP test suggested a potential benefit of the PEGB on working memory. However, this hypothesis should be further investigated to confirm this cognitive effect.

Learning ability in aged beagle dogs is preserved by behavioral enrichment and dietary fortification: a two-year longitudinal study.

The effectiveness of two interventions, dietary fortification with antioxidants and a program of behavioral enrichment, was assessed in a longitudinal study of cognitive aging in beagle dogs. A baseline protocol of cognitive testing was used to select four cognitively equivalent groups: control food-control experience (C-C), control food-enriched experience (C-E), antioxidant fortified food-control experience (A-C), and antioxidant fortified food-enriched experience(A-E). We also included two groups of young behaviorally enriched dogs, one receiving the control food and the other the fortified food. Discrimination learning and reversal was assessed after one year of treatment with a size discrimination task, and again after two years with a black/white discrimination task. The four aged groups were comparable at baseline. At one and two years, the aged combined treatment group showed more accurate learning than the other aged groups. Discrimination learning was significantly improved by behavioral enrichment. Reversal learning was improved by both behavioral enrichment and dietary fortification. By contrast, the fortified food had no effect on the young dogs. These results suggest that behavioral enrichment or dietary fortification with antioxidants over a long-duration can slow age-dependent cognitive decline, and that the two treatments together are more effective than either alone in older dogs.

Dog-appeasing pheromone collars reduce sound-induced fear and anxiety in beagle dogs: a placebo-controlled study.

The objective of the study was to assess the effects of a dog-appeasing pheromone (DAP) collar in reducing sound-induced fear and anxiety in a laboratory model of thunderstorm simulation. Twenty-four beagle dogs naïve to the current test were divided into two treatment groups (DAP and placebo) balanced on their fear score in response to a thunderstorm recording. Each group was then exposed to two additional thunderstorm simulation tests on consecutive days. Dogs were video-assessed by a trained observer on a 6-point scale for active, passive and global fear and anxiety (combined). Both global and active fear and anxiety scores were significantly improved during and following thunder compared with placebo on both test days. DAP significantly decreased global fear and anxiety across 'during' and 'post' thunder times when compared with baseline. There was no significant improvement in the placebo group from baseline on the test days. In addition, the DAP group showed significantly greater use of the hide box at any time with increased exposure compared with the placebo group. The DAP collar reduced the scores of fear and anxiety, and increased hide use in response to a thunder recording, possibly by counteracting noise-related increased reactivity.

Visual-discrimination learning ability and beta-amyloid accumulation in the dog.

Young, middle-aged, and old beagle dogs were tested on several visual-discrimination tasks: reward- and object-approach learning, object discrimination and reversal, long-term retention of a reversal problem, and a size-discrimination task. Beta-amyloid accumulation in the entorhinal, prefrontal, parietal, and occipital cortices was quantified using immunohistochemical and imaging techniques at the conclusion of cognitive testing. Middle-aged and old dogs were impaired in size-discrimination learning. In each task, a subset of aged dogs was impaired relative to age-matched peers. Beta-amyloid accumulation was age-dependent. However, not all middle-aged and old dogs showed beta-amyloid accumulation in the entorhinal cortex. The error scores from dogs tested with a nonpreferred object during visual discrimination learning and from reversal learning were correlated with beta-amyloid in the prefrontal but not entorhinal cortex. Size-discrimination and reward and object-approach learning error scores were correlated with beta-amyloid accumulation in the entorhinal but not prefrontal cortex. The results of these studies support an association between cognitive test and the location and extent of beta-amyloid pathology.

Region-specific age at onset of beta-amyloid in dogs.

Cortical patterns of beta-amyloid (Abeta) deposition were evaluated in 40 beagle dogs ranging in age from 2 to 18 years. Abeta deposition in the prefrontal, occipital, parietal and entorhinal cortices was visualized by using an antibody against Abeta1-42. A logistic regression was used to estimate differences in age-at-onset and rate of deposition of Abeta as a function of brain region. The earliest and most consistent site of Abeta deposition with age was in the prefrontal cortex. Entorhinal Abeta deposition was not consistently observed until the age of 14 years, but was present in a subset of dogs under the age of 14 years. These regional vulnerabilities to Abeta accumulation are similar to those seen in the aging human. By using parameters derived from regression analyses, it may be possible to predict the presence of Abeta within specific brain regions in individual dogs. We propose that these models will be a useful tool to evaluate interventions that delay the age of onset or slow the rate of accumulation of Abeta in the dog.

The canine as an animal model of human aging and dementia.

The aged canine displays many features that make it an excellent model for studying the progression of pathology in brain aging and linking these findings to learning, memory and other cognitive functions. Canines develop extensive beta-amyloid deposition within neurons and their synaptic fields, which appears to give rise to senile plaques. These plaques are primarily of the early diffuse subtype. Aged canines also exhibit accumulations of lipofuscin, cerebral vascular changes, dilation of the ventricles, and cytoskeletal changes. Neurofibrillary tangles (NFTs) are not present in the aged canine. Thus, the aged canine brain provides a suitable model for studying early degeneration normally considered to be pre-Alzheimer's. This supposition is also supported by behavioral data. We have found that the extent of beta-amyloid deposition correlates with a decline in select measures of cognitive function. These data provide the first evidence of a correlation between beta-amyloid accumulation and cognitive decline in the absence of NFTs. We summarize four lines of evidence that support using the aged canine as a model of human aging: (a) Aged canines develop aspects of neuropathology similar to that observed in aged humans; (b) Veterinarians have observed that many canines exhibit a clinical syndrome of age-related cognitive dysfunction; (c) Aged canines are deficient on a variety of neuropsychological tests of cognitive function; (d) The level of beta-amyloid accumulation correlates with cognitive dysfunction in the canine. These data indicate that the aged canine is a particularly useful model for studying age-related cognitive dysfunction (ARCD), early neuronal changes associated with aging, and the initial stages of senile plaque formation.

Dietary enrichment counteracts age-associated cognitive dysfunction in canines.

Advanced age is accompanied by cognitive decline indicative of central nervous system dysfunction. One possibly critical causal factor is oxidative stress. Accordingly, we studied the effects of dietary antioxidants and age in a canine model of aging that parallels the key features of cognitive decline and neuropathology in humans. Old and young animals were placed on either a standard control food, or a food enriched with a broad spectrum of antioxidants and mitochondrial enzymatic cofactors. After 6 months of treatment, the animals were tested on four increasingly difficult oddity discrimination learning problems. The old animals learned more slowly than the young, making significantly more errors. However, this age-associated decline was reduced in the animals fed the enriched food, particularly on the more difficult tasks. These results indicate that maintenance on foods fortified with complex mixtures of antioxidants can partially counteract the deleterious effects of aging on cognition.

Diffuse plaques contain C-terminal A beta 42 and not A beta 40: evidence from cats and dogs.

Recent reports have suggested that beta-amyloid (A beta) species of variable length C-termini are differentially deposited within early and late-stage plaques and the cerebrovasculature. Specifically, longer C-terminal length A beta 42/3 fragments (i.e., A beta forms extending to residues 42 and/or 43) are thought to be predominant within diffuse plaques while both A beta 42/3 and A beta 40 (A beta forms terminating at residue 40) are present within a subset of neuritic plaques and cerebrovascular deposits. We sought to clarify the issue of differential A beta deposition using aged canines, a partial animal model of Alzheimer's disease that exhibits extensive diffuse plaques and frequent vascular amyloid, but does not contain neuritic plaques or neurofibrillary tangles. We examined the brains of 20 aged canines, 3 aged felines, and 17 humans for the presence of A beta immunoreactive plaques, using antibodies to A beta 1(-17), A beta 17(-24), A beta 1(-28), A beta 40, and A beta 42. We report that plaques within the canine and feline brain are immunopositive for A beta 42 but not A beta 40. This is the first observation of nascent AD pathology in the aged feline brain. Canine plaques also contained epitopes within A beta 1(-17), A beta 17(-24), and A beta 1(-28). In all species examined, vascular deposits were immunopositive for both A beta 40 and A beta 42. In the human brain, diffuse plaques were preferentially A beta 42 immunopositive, while neuritic plaques and vascular deposits were both A beta 40 and A beta 42 immunopositive. However, not all neuritic plaques contain A beta 40 epitopes.

Activation of AP5-sensitive NMDA Receptors is Not Required to Induce LTP of Synaptic Transmission in the Lateral Perforant Path.

The role of the N-methyl-d-aspartate (NMDA) type of glutamate receptor in long-term potentiation (LTP) of the medial (MPP) and lateral (LPP) divisions of the perforant path - granule cell system was investigated in urethane-anaesthetized rats. A stimulating electrode was positioned in the dorsomedial or ventrolateral aspect of the angular bundle for selective activation of either the MPP or LPP, respectively. A push - pull cannula served to focally perfuse artificial cerebrospinal fluid (ACSF) across the perforant path synaptic zone, while evoked potentials were monitored in the dentate hilus. Identification of LPP and MPP responses was based on (1) differences in population excitatory postsynaptic potential (EPSP) waveform obtained during stimulus depth profiles, and (2) differential sensitivity of evoked EPSPs to the glutamate receptor agonist l-aminophosphonobutyrate (AP4), and the antagonist gamma-d-glutamylglycine (DGG). High-frequency stimulation (400 Hz, 8 bursts of 8 pulses) applied to the lateral and medial perforant path elicited LTP of the EPSP and population spike in rats perfused with standard medium. In the MPP, LTP was almost completely blocked when d-aminophosphonopentanoate (AP5; 100 microM), a selective NMDA receptor antagonist, was perfused during the tetanus. Surprisingly, in the LPP experiments, AP5 did not impair induction of the 'synaptic' EPSP component of LTP. This occurred despite the ability of AP5 to block LTP of the LPP evoked population spike. The results suggest the existence of a novel, NMDA receptor-independent form of synaptic LTP in the lateral perforant path.

Ultrastructural evidence of fibrillar beta-amyloid associated with neuronal membranes in behaviorally characterized aged dog brains.

The aged dog brain accumulates beta-amyloid in the form of diffuse senile plaques, which provides a potentially useful in vivo model system for studying the events surrounding the deposition of beta-amyloid. We used postembedding immunocytochemistry at the electron microscopic level to determine the subcellular distribution of beta-amyloid 1-40 and beta-amyloid 1-42 peptides in the prefrontal and parietal cortex of behaviorally characterized dogs ranging in age from one to 17 years. Immunogold particles signaling beta-amyloid 1-42 occurred over intracellular and extracellular fibrils that were approximately 8 nm in width. Intracellular beta-amyloid 1-42 fibrils were found in close proximity to glial fibrillary acidic protein fibers within astrocytes, but only in cells with signs of plasma membrane disruption. Neuronal labeling of beta-amyloid 1-42 appears to be associated with the plasma membrane. Membrane-bound beta-amyloid 1-42 occurs in the form of fine fibrils that are embedded in the dendritic membrane and appear to project into the extracellular space as determined by quantitative analysis of the immunogold particle distribution. Bundles of beta-amyloid 1-42 were also closely associated and/or integrated with degenerating myelin sheaths of axons. In one dog that was impaired on several cognitive tasks, extensive beta-amyloid 1-42 deposition was associated with microvacuolar changes and vascular pathology. The present findings suggest that beta-amyloid 1-42 may be generated at the dendritic plasma membrane as well as in intracellular compartments. The close association between beta-amyloid 1-42 and destroyed myelin suggests one possible new mechanism by which beta-amyloid 1-42 induces neurodegeneration.

Seizure activity results in increased tyrosine phosphorylation of the N-methyl-D-aspartate receptor in the hippocampus.

Systemic administration of kainic acid (KA) induces status epilepticus (SE) that causes neurodegeneration and may subsequently lead to spontaneous recurrent seizures. We investigated the effects of KA-induced SE on tyrosine phosphorylation and solubility properties of the NMDA receptor. Following 1 h of SE, total protein tyrosine phosphorylation was elevated in both the hippocampus and frontal cortex relative to controls. Tyrosine phosphorylation of the NMDA receptor subunits NR2A and NR2B was also enhanced following SE. Animals that received KA but did not develop SE, did not exhibit increased tyrosine phosphorylation. SE resulted in a decrease in the solubility of NMDA receptor subunits and of PSD-95 in 1% deoxycholate. In contrast, the detergent solubility of AMPA and kainate receptors was not affected. These findings demonstrate that SE alters tyrosine phosphorylation of the NMDA receptor, and indicate that the interaction of the NMDA receptor with other components of the NMDA receptor complex are altered as a consequence of seizure activity.

Mechanisms underlying the plasticity of hippocampal stimulation-induced reward.

It has been reported that the very slow acquisition of hippocampal self-stimulation can be markedly facilitated by pretreatment with a program of repeated daily hippocampal stimulation (kindling). Three experiments were performed to investigate the neurophysiological basis of this effect. Experiment 1 demonstrated that unilateral stimulation pretreatment produced a facilitation of learning to lever press for stimulation delivered to the contralateral hippocampal electrode. Thus, there is a transfer of facilitation. In Experiment 2 it was shown that this transfer effect was not affected by lesion of the originally kindled focus, a result suggesting that the facilitated acquisition was not due to feedback to the kindled site. In Experiment 3 electrical activity during hippocampal self-stimulation was examined in order to explore the possible correlation between hippocampal reward and epileptiform activity. No relation was apparent: Lever pressing persisted even when no afterdischarge was elicited. The findings of these experiments are consistent with the hypothesis that the facilitatory effect of stimulation reflects the development of transsynaptic potentiation.

Cognitive functions and aging in the dog: acquisition of nonspatial visual tasks.

Old, middle-aged, and young dogs were compared on discrimination and reversal learning and on acquisition of a delayed-nonmatching-to-sample (DNMS) test of recognition memory. DNMS acquisition was acquired more rapidly by young dogs. Reversal deficits were found between aged mixed-breed dogs and young beagles, but not between old and young beagles. Aged beagles also showed unexpected deficits in reward approach and object approach learning. Aged mixed-breed dogs did not show deficits in reward approach and object approach learning, but they learned the discrimination task more slowly than the age-matched beagles. A detailed analysis of response patterns indicated that once present, the development of side preferences contributed to deficits of old dogs in discrimination learning. In the discrimination reversal, old dogs were more persistent in responding to the previously rewarded stimulus object. Findings suggest that the dog, like other species, shows age-dependent deterioration in cognitive function, the extent of deterioration is a function of both task and previous experience, and at least part of the deterioration is a result of increased behavioral rigidity. Results also indicate that it is important to control for breed differences and previous experience.

Spatial learning and memory as a function of age in the dog.

Spatial learning and memory were studied in dogs of varying ages and sources. Compared to young dogs, a significantly higher proportion of aged dogs could not acquire a spatial delayed nonmatching-to-sample task. A regression analysis revealed a significant age effect during acquisition. Spatial memory was studied by comparing performance at delay interval of 20, 70, and 110 s. At short delays aged and young dogs were similar; at longer delays, errors increased to a greater extent in old than in young dogs; however this was not statistically significant. It was possible to identify 2 groups of aged animals, age-impaired and age-unimpaired. Several of the dogs were also tested on an object recognition memory task, which was more difficult to learn than the spatial task. The possibility that these findings are confounded by breed differences is considered. Overall, the present results provide further evidence of the value of a canine model of aging.

Dose-specific effects of scopolamine on canine cognition: impairment of visuospatial memory, but not visuospatial discrimination.

RATIONALE: The cholinergic system is linked extensively to memory, but its exact role remains controversial. In particular, scopolamine-induced impairment in rodents is not task specific, which may be due to difficulty in developing rodent protocols to assess deficits in recent memory, in which the remembered event is brief and distinct, and/or to non-specific behavioral impairment. OBJECTIVES: The present study sought to determine whether scopolamine-induced deficits in recent memory, using a working memory task, could be dose-specifically dissociated from deficits in associative memory in dogs. METHODS: A Latin-square design was used to determine the effect of scopolamine (5, 10 and 15 microg/kg; SC) on a variable delayed-non-matching-to-position (DNMP) task, which assesses visuospatial working memory. Subsequently, the minimal effective dose (15 microg/kg; SC) was administered prior to testing on a landmark discrimination task, which provides a measure of allocentric spatial ability, a black-white discrimination task, an oddity discrimination task and tests of exploratory behavior. We also investigated the effects of a 30 microg/kg dose (SC) on tests of oddity discrimination and behavioral activity. RESULTS: A 15 microg/kg dose produced significant impairment on the DNMP task, but did not affect performance of any discrimination task and did not alter behavior on tests of open field or curiosity. A 30 microg/kg dose caused disruption on discrimination performance and on open field measures. CONCLUSIONS: Working memory performance is most sensitive to scopolamine-induced impairment and can be dissociated from scopolamine-induced deficits in discrimination performance and non-cognitive behaviors. The present results indicate that scopolamine-induced impairments of working memory in the dog can serve as a model of age-related cholinergic dysfunction.

Short intertrial intervals impair water maze performance in old Fischer 344 rats.

Male and female Fischer 344 rats (N = 55) aged approximately 18, 21, and 24 months were tested for spatial learning in the water maze with intertrial intervals of 1-4 min (Massed) or 23-33 min (Spaced). Animals tested in the Massed condition showed an age-related impairment on trials to criterion; rats aged 24 months performed more poorly than younger subjects. Spaced animals did not differ at any age nor did they differ from 18- or 21-month-old Massed subjects. The youngest rats in both groups were comparable to animals aged 7-8 months tested under Massed conditions. Tests on swim distance, swim speed, and escape latency produced similar results. Our data suggest that acquisition deficits in 24-month-old rats tested with long intertrial intervals are due at least in part to increased susceptibility to fatigue and/or thermal stress. Caution should be used, therefore, when interpreting age-related impairments in water maze performance.