Frontal lobe volume, function, and beta-amyloid pathology in a canine model of aging

Aging in the canine and feline brain

Aging dogs and cats show neurodegenerative features that are similar to human aging and Alzheimer disease. Neuropathologic changes with age may be linked to signs of cognitive dysfunction both in the laboratory and in a clinic setting. Less is known about cat brain aging and cognition and this represents an area for further study. Neurodegenerative diseases such as lysosomal storage diseases in dogs and cats also show similar features of human aging, suggesting some common underlying pathogenic mechanisms and also suggesting pathways that can be modified to promote healthy brain aging.

Effect of Resveratrol as Caloric Restriction Mimetic and Environmental Enrichment on Neurobehavioural Responses in Young Healthy Mice

Caloric restriction and environmental enrichment have been separately reported to possess health benefits such as improvement in motor and cognitive functions. Resveratrol, a natural polyphenolic compound, has been reported to be caloric restriction mimetic. This study therefore aims to investigate the potential benefit of the combination of resveratrol as CR and EE on learning and memory, motor coordination, and motor endurance in young healthy mice. Fifty mice of both sexes were randomly divided into five groups of 10 animals each: group I animals received carboxymethylcellulose (CMC) orally per kg/day (control), group II animals were maintained on every other day feeding, group III animals received resveratrol 50 mg/kg, suspended in 10 g/L of (CMC) orally per kg/day, group IV animals received CMC and were kept in an enriched environment, and group V animals received resveratrol 50 mg/kg and were kept in EE. The treatment lasted for four weeks. On days 26, 27, and 28 of the study period, the animals were subjected to neurobehavioural evaluation. The results obtained showed that there was no significant change (P>0.05) in neurobehavioural responses in all the groups when compared to the control which indicates that 50 mg/kg of resveratrol administration and EE have no significant effects on neurobehavioural responses in young healthy mice over a period of four weeks.

Prevention approaches in a preclinical canine model of Alzheimer's disease: benefits and challenges

Aged dogs spontaneously develop many features of human aging and Alzheimer's disease (AD) including cognitive decline and neuropathology. In this review, we discuss age-dependent learning tasks, memory tasks, and functional measures that can be used in aged dogs for sensitive treatment outcome measures. Neuropathology that is linked to cognitive decline is described along with examples of treatment studies that show reduced neuropathology in aging dogs (dietary manipulations, behavioral enrichment, immunotherapy, and statins). Studies in canine show that multi-targeted approaches may be more beneficial than single pathway manipulations (e.g., antioxidants combined with behavioral enrichment). Aging canine studies show good predictive validity for human clinical trials outcomes (e.g., immunotherapy) and several interventions tested in dogs strongly support a prevention approach (e.g., immunotherapy and statins). Further, dogs are ideally suited for prevention studies as they the age because onset of cognitive decline and neuropathology strongly support longitudinal interventions that can be completed within a 3-5 year period. Disadvantages to using the canine model are that they lengthy, use labor-intensive comprehensive cognitive testing, and involve costly housing (almost as high as that of non-human primates). However, overall, using the dog as a preclinical model for testing preventive approaches for AD may complement work in rodents and non-human primates.

Exercise enhances memory consolidation in the aging brain

Exercise has been shown to reduce age-related losses in cognitive function including learning and memory, but the mechanisms underlying this effect remain poorly understood. Memory formation occurs in stages that include an initial acquisition phase, an intermediate labile phase, and then a process of consolidation which leads to long-term memory formation. An effective way to examine the mechanism by which exercise improves memory is to introduce the intervention (exercise), post-acquisition, making it possible to selectively examine memory storage and consolidation. Accordingly we evaluated the effects of post-trial exercise (10 min on a treadmill) on memory consolidation in aged canines both right after, an hour after, and 24 h after acute exercise training in concurrent discrimination, object location memory (OLM), and novel object recognition tasks. Our study shows that post-trial exercise facilitates memory function by improving memory consolidation in aged animals in a time-dependent manner. The improvements were significant at 24 h post-exercise and not right after or 1 h after exercise. Aged animals were also tested following chronic exercise (10 min/day for 14 consecutive days) on OLM or till criterion were reached (for reversal learning task). We found improvements from a chronic exercise design in both the object location and reversal learning tasks. Our studies suggest that mechanisms to improve overall consolidation and cognitive function remain accessible even with progressing age and can be re-engaged by both acute and chronic exercise.

A canine model of human aging and Alzheimer's disease

The aged dog naturally develops cognitive decline in many different domains (including learning and memory) but also exhibits human-like individual variability in the aging process. The neurobiological basis for cognitive dysfunction may be related to structural changes that reflect neurodegeneration. Molecular cascades that contribute to degeneration in the aging dog brain include the progressive accumulation of beta-amyloid (Aβ) in diffuse plaques and in the cerebral vasculature. In addition, neuronal dysfunction occurs as a consequence of mitochondrial dysfunction and cumulative oxidative damage. In combination, the aged dog captures key features of human aging, making them particularly useful for the development of preventive or therapeutic interventions to improve aged brain function. These interventions can then be translated into human clinical trials. This article is part of a Special Issue entitled: Animal Models of Disease.

Clinical signs and management of anxiety, sleeplessness, and cognitive dysfunction in the senior pet

Physical signs of old age may be obvious, but mental and cognitive changes require more careful observation. Changes in behavior may represent the earliest indications of medical problems, or disorders of the central nervous system, and these may be bidirectional. Cognitive dysfunction syndrome is underdiagnosed and affects a substantial portion of aged companion animals. This article describes potential treatment regimens to address age-related behavioral problems, as well as a framework for investigating differential diagnoses. Early identification of changes in behavior is essential for the adequate treatment and management of medical and behavioral problems, and for monitoring outcomes.

Cholinesterase inhibitors improve both memory and complex learning in aged beagle dogs

Similar to patients with Alzheimer's disease (AD), dogs exhibit age-dependent cognitive decline, amyloid-β (Aβ) pathology, and evidence of cholinergic hypofunction. The present study sought to further investigate the role of cholinergic hypofunction in the canine model by examining the effect of the cholinesterase inhibitors phenserine and donepezil on performance of two tasks, a delayed non-matching-to-position task (DNMP) designed to assess working memory, and an oddity discrimination learning task designed to assess complex learning, in aged dogs. Phenserine (0.5 mg/kg; PO) significantly improved performance on the DNMP at the longest delay compared to wash-out and partially attenuated scopolamine-induced deficits (15 μg/kg; SC). Phenserine also improved learning on a difficult version of an oddity discrimination task compared to placebo, but had no effect on an easier version. We also examined the effects of three doses of donepezil (0.75, 1.5, and 6 mg/kg; PO) on performance of the DNMP. Similar to the results with phenserine, 1.5 mg/kg of donepezil improved performance at the longest delay compared to baseline and wash-out, indicative of memory enhancement. These results further extend the findings of cholinergic hypofunction in aged dogs and provide pharmacological validation of the canine model with a cholinesterase inhibitor approved for use in AD. Collectively, these studies support utilizing the aged dog in future screening of therapeutics for AD, as well as for investigating the links among cholinergic function, Aβ pathology, and cognitive decline.

White matter myelin loss in the brains of aged dogs

The significance of cerebral white matter (WM) demyelination in the cognitive decline of elderly humans is disputed. Cognitive decline also occurs in aged dogs, although the age-related changes that occur in the canine cerebral WM are yet to be studied, particularly with regard to their relevance to the WM alterations of elderly humans. The present study revealed age-dependent myelin loss in the frontal lobe WM of canine brains. The accumulation of ceroid-lipofuscin-laden phagocytes was observed in the perivascular spaces of the WM and was correlated with the decrease in myelination. Also, myelin basic protein was detected in some of the vacuoles of these phagocytes. In the WM, beta-amyloid (Aβ) was deposited focally in capillary walls, and colocalized with apolipoprotein E (Apo E). Note that the dog is homozygous for Apo E4, which genotype is related to capillary CAA in humans. These findings indicate that WM demyelination occurs in aged dogs as well as in aged humans, hence WM alterations may account for age-related behavioral changes of the dog. In conclusion, dogs are useful for chronological studies of age-related WM changes.

Neurobiology of the aging dog

Aged canines naturally accumulate several types of neuropathology that may have links to cognitive decline. On a gross level, significant cortical atrophy occurs with age along with an increase in ventricular volume based on magnetic resonance imaging studies. Microscopically, there is evidence of select neuron loss and reduced neurogenesis in the hippocampus of aged dogs, an area critical for intact learning and memory. The cause of neuronal loss and dysfunction may be related to the progressive accumulation of toxic proteins, oxidative damage, cerebrovascular pathology, and changes in gene expression. For example, aged dogs naturally accumulate human-type beta-amyloid peptide, a protein critically involved with the development of Alzheimer's disease in humans. Further, oxidative damage to proteins, DNA/RNA and lipids occurs with age in dogs. Although less well explored in the aged canine brain, neuron loss, and cerebrovascular pathology observed with age are similar to human brain aging and may also be linked to cognitive decline. Interestingly, the prefrontal cortex appears to be particularly vulnerable early in the aging process in dogs and this may be reflected in dysfunction in specific cognitive domains with age.

Enhancing brain functions in senior dogs: a new nutritional approach

Aging induces many morphological and metabolic changes in the brain, which may eventually lead to cognitive impairment and dementia called cognitive dysfunction syndrome in senior dogs. Cognitive impairment and dementia can adversely affect the quality of life in both dogs and their owners. Progress has been made over the past years to understand how aging affects brain and its functions in humans and animals including dogs. Existing data indicate that aging-induced changes in the brain are gradual and irreversible. Therefore, it is too late to effectively manage dogs with cognitive impairment and cognitive dysfunction syndrome. The best option to manage brain aging successfully is to reduce or prevent aging-induced changes in the brain by correcting early metabolic changes and eliminating risk factors associated with brain aging and dementia. This article reviews behavioral, morphological, and metabolic changes in the brain induced by aging and discusses a novel nutritional solution for the aging-induced metabolic changes in the brain.

Different CSF β-amyloid processing in Alzheimer's and Creutzfeldt-Jakob disease

Decreased levels of β-amyloid (Aβ) 1-42 in cerebrospinal fluid (CSF) are characteristic for Alzheimer's disease (AD) and are also evident in Creutzfeldt-Jakob disease (CJD). Aβ plaques are thought to be responsible for this decrease in AD patients, whereas such Aβ plaques are rarely seen in CJD. To investigate the Aβ pattern in brain and CSF of neuropathologically confirmed CJD and AD patients we used an electrophoretic method to investigate Aβ peptide fractions which are not accessible to ELISA and immunohistochemistry. We analyzed Aβ peptides in the CSF of autopsy-confirmed CJD and AD patients and the corresponding brain homogenates using a quantitative urea-based Aβ electrophoresis immunoblot (Aβ-SDS-PAGE/immunoblot).The CSF Aβ1-42 decrease correlated with the brain Aβ load in AD, but not in CJD. There was no difference in the soluble fractions of brain homogenate in AD and CJD. We therefore conclude that different mechanisms in AD and CJD are responsible for the Aβ1-42 decrease in the CSF.

Cognitive dysfunction in cats: a syndrome we used to dismiss as 'old age'

PRACTICAL RELEVANCE

Cognitive dysfunction syndrome (CDS) is a widely accepted diagnosis in dogs, with established treatment options. In cats, however, our understanding of cognitive dysfunction is still being shaped by ongoing research in the field, and limited treatment options are available. Recent clinical studies indicate that old age in the cat is accompanied by increased behavioural signs such as wandering, vocalization and night-time activity that are not attributable to identifiable medical problems. It is essential, therefore, that veterinarians include behavioural well-being in the routine care of senior cats.

PATIENT GROUP

While the exact age of onset is not established, studies suggest that age-related behavioural changes consistent with cognitive dysfunction are prevalent in cats as early as 10 years of age and that prevalence increases significantly in older cats.

CLINICAL CHALLENGES

The diagnosis of cognitive dysfunction requires the identification of geriatric behavioural changes that are not caused by other medical problems, although the two may not be mutually exclusive. Therefore, the practitioner must rely heavily on owner reports and history to ensure prompt diagnosis and treatment. The absence of any approved dietary or pharmaceutical interventions for cognitive dysfunction adds a further challenge, although several possibilities exist.

EVIDENCE BASE

This article draws on recent research that has produced neuropathological, cognitive and behavioural evidence for cognitive dysfunction in aging cats. As an impetus to further our understanding of this disease and potential treatment options, the authors propose a behavioural checklist that might aid in the clinical diagnosis of feline CDS and discuss treatment options that have proven successful in the canine counterpart of this disease.

Clinical magnetic resonance volumetry of the hippocampus in 58 epileptic dogs

Hippocampal atrophy, which is a component of hippocampal sclerosis and recognized commonly in human intractable epilepsy, is controversial in canine epilepsy. We examined the hippocampal volume in 58 epileptic dogs and 35 control dogs using magnetic resonance (MR) images, and calculated the relative hippocampal volume asymmetry of the right and left hippocampus. Subjectively, there were visible MR imaging abnormalities in seven of the 58 epileptic dogs (12%). The hippocampel volume asymmetric ratio of epileptic dogs (5.84 +/- 4.47%) was significantly greater than that of control dogs (1.62 +/- 0.88%). Using a cutoff threshold asymmetric ratio of 6% that is indicated in human epilepsy, 28 epileptic dogs (48%) were characterized as having unilateral hippocampus atrophy. The hippocampal volume asymmetry ratio cannot be used to detect bilateral atrophy. In conclusion, although less frequent than that observed in human epilepsy patients, hippocampal atrophy may occur in canine epilepsy.

Effects of hypercapnia, hypocapnia, and hyperoxemia on brain morphometrics determined by use of T1-weighted magnetic resonance imaging in isoflurane-anesthetized dogs

OBJECTIVE

To evaluate the effects of various combinations of PaCO2 and PaO2 values on brain morphometrics.

ANIMALS

6 healthy adult dogs.

PROCEDURES

A modified Latin square design for randomization was used. Dogs were anesthetized with propofol (6 to 8 mg/kg, IV), and anesthesia was maintained with isoflurane (1.7%) and atracurium (0.2 mg/kg, IV, q 30 min). Three targeted values of PaCO2 (20, 40, and 80 mm Hg) and 2 values of PaO2 (100 and 500 mm Hg) were achieved in each dog, yielding 6 combinations during a single magnetic resonance (MR) imaging session. When the endpoints were reached, dogs were given at least 5 minutes for physiologic variables to stabilize before T1-weighted MR images were obtained. Total brain volume (TBV) and lateral ventricular volume (LVV) were calculated from manually drawn contours of areas of interest by use of a software program, with each dog serving as its own control animal. Three blinded investigators subjectively evaluated the lateral ventricular size (LVS) and the cerebral sulci width (CSW). Brain morphometric values were compared among the target blood gas states.

RESULTS

No significant differences in TBV were found among target states. The LVV was significantly greater during hypocapnia, compared with hypercapnia at the same PaO2 value. With regard to the subjective evaluations, there were no significant differences among evaluators or among combinations of PaO2 and PaCO2 values.

CONCLUSIONS AND CLINICAL RELEVANCE

The changes observed in LVV during hypocapnia and hypercapnia may serve as a potential confounding factor when neuromorphometric evaluations are performed in anesthetized dogs.

Synergistic effects of long-term antioxidant diet and behavioral enrichment on beta-amyloid load and non-amyloidogenic processing in aged canines

A long-term intervention (2.69 years) with an antioxidant diet, behavioral enrichment, or the combined treatment preserved and improved cognitive function in aged canines. Although each intervention alone provided cognitive benefits, the combination treatment was additive. We evaluate the hypothesis that antioxidants, enrichment, or the combination intervention reduces age-related beta-amyloid (Abeta) neuropathology, as one mechanism mediating observed functional improvements. Measures assessed were Abeta neuropathology in plaques, biochemically extractable Abeta(40) and Abeta(42) species, soluble oligomeric forms of Abeta, and various proteins in the beta-amyloid precursor protein (APP) processing pathway. The strongest and most consistent effects on Abeta pathology were observed in animals receiving the combined antioxidant and enrichment treatment. Specifically, Abeta plaque load was significantly decreased in several brain regions, soluble Abeta(42) was decreased selectively in the frontal cortex, and a trend for lower Abeta oligomer levels was found in the parietal cortex. Reductions in Abeta may be related to shifted APP processing toward the non-amyloidogenic pathway, because alpha-secretase enzymatic activity was increased in the absence of changes in beta-secretase activity. Although enrichment alone had no significant effects on Abeta, reduced Abeta load and plaque maturation occurred in animals receiving antioxidants as a component of treatment. Abeta measures did not correlate with cognitive performance on any of the six tasks assessed, suggesting that modulation of Abeta alone may be a relatively minor mechanism mediating cognitive benefits of the interventions. Overall, the data indicate that multidomain treatments may be a valuable intervention strategy to reduce neuropathology and improve cognitive function in humans.

Development of a morphometric magnetic resonance image parameter suitable for distinguishing between normal dogs and dogs with cerebellar atrophy

Neurodegenerative diseases affect the cerebellum of numerous dog breeds. Although subjective, magnetic resonance (MR) imaging has been used to detect cerebellar atrophy in these diseases, but there are few data available on the normal size range of the cerebellum relative to other brain regions. The purpose of this study was to determine whether the size of the cerebellum maintains a consistent ratio with other brain regions in different ages and breeds of normal dogs and to define a measurement that can be used to identify cerebellar atrophy on MR images. Images from 52 normal and 13 dogs with cerebellar degenerative diseases were obtained. Volume and mid-sagittal cross-sectional area of the forebrain, brainstem, and cerebellum were calculated for each normal dog and compared between different breeds and ages as absolute and relative values. The ratio of the cerebellum to total brain and of the brainstem to cerebellum mid-sagittal cross-sectional area was compared between normal and affected dogs and the sensitivity and specificity of these ratios at distinguishing normal from affected dogs was calculated. The percentage of the brain occupied by the cerebellum in diverse dog breeds between 1 and 5 years of age was not significantly different, and cerebellar size did not change with increasing age. Using a cut off of 89%, the ratio between the brainstem and cerebellum mid-sagittal cross-sectional area could be used successfully to differentiate affected from unaffected dogs with a sensitivity and specificity of 100%, making this ratio an effective tool for identifying cerebellar atrophy on MR images.

Magnetic resonance imaging of the canine brain at 7 T

The purpose of this study was to describe relevant canine brain structures as seen on T2-weighted images following magnetic resonance (MR) imaging at 7 T and to compare the results with imaging at 1.5 T. Imaging was performed on five healthy laboratory beagle dogs using 1.5 and 7 T clinical scanners. At 1.5 T, spin echo images were acquired, while gradient echo images were acquired at 3 T. Image quality and conspicuity of anatomic structures were evaluated qualitatively by direct comparison of the images obtained from the two different magnetic fields. The signal-to-nose ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared between 1.5 and 7 T. The T2-weighted images at 7 T provided good spatial and contrast resolution for the identification of clinically relevant brain anatomy; these images provided better delineation and conspicuity of the brain stem and cerebellar structures, which were difficult to unequivocally identify at 1.5 T. However, frontal and parietal lobe and the trigeminal nerve were difficult to identify at 7 T due to susceptibility artifact. The SNR and CNR of the images at 7 T were significantly increased up to 318% and 715% compared with the 1.5 T images. If some disadvantages of 7 T imaging, such as susceptibility artifacts, technical difficulties, and high cost, can be improved, 7 T clinical MR imaging could provide a good experimental and diagnostic tool for the evaluation of canine brain disorders.

Rhesus macaque brain morphometry: a methodological comparison of voxel-wise approaches

Voxel-based morphometry studies have become increasingly common in human neuroimaging over the past several years; however, few studies have utilized this method to study morphometry changes in non-human primates. Here we describe the application of voxel-wise morphometry methods to the rhesus macaque (Macaca mulatta) using the 112RM-SL template and priors (McLaren et al. (2009) [42]) and as an illustrative example we describe age-associated changes in grey matter morphometry. Specifically, we evaluated the unified segmentation routine implemented using Statistical Parametric Mapping (SPM) software and the FMRIB's Automated Segmentation Tool (FAST) in the FMRIB Software Library (FSL); the effect of varying the smoothing kernel; and the effect of the normalization routine. We found that when studying non-human primates, brain images need less smoothing than in human studies, 2-4mm FWHM. Using flow field deformations (DARTEL) improved inter-subject alignment leading to results that were more likely due to morphometry differences as opposed to registration differences.

Age-dependent decline of blood-brain barrier P-glycoprotein expression in the canine brain

The efflux transporter P-glycoprotein serves as a major molecular gatekeeper at the blood-brain barrier. It has been suggested that a reduction of P-glycoprotein activity with aging might enhance exposure of brain tissue to exogenous and endogenous compounds thereby contributing to the development of neurodegenerative diseases. Brain tissue from owner-kept dogs renders an excellent tool to study the impact of aging on the background of variable environmental and genetic influencing factors. Therefore, we determined expression rates of P-glycoprotein in canine post-mortem tissue from 23 non-laboratory dogs. P-glycoprotein expression in the parahippocampal cortex exhibited a negative correlation with age. Analysis of the area labeled for P-glycoprotein in dogs aged >100 months revealed a 72% drop in P-glycoprotein expression as compared to young adults aged 23-36 months. Respective data from the dentate hilus and dentate gyrus indicated an earlier drop with a reduction by 77 and 80% in dogs aged 37-99 months in comparison with younger individuals. In contrast to the decline observed with aging in dogs without plaques, P-glycoprotein expression rates rather tended to increase with further aging in dogs with plaque formation. In conclusion, the thorough analysis of P-glycoprotein expression rates in non-laboratory dogs revealed a significant decline with aging. The data strongly support the concept that age-dependent changes might predispose to neurodegenerative diseases. In the early pathogenesis of Alzheimer's disease which is modelled by diffuse plaques in the canine brain, an up-regulation of P-glycoprotein might act as a compensatory mechanism to enhance Abeta efflux from the brain. Future studies are necessary to further evaluate the correlation between Abeta deposits and P-glycoprotein expression in different phases of the disease.

Strategies for improving cognition with aging: insights from a longitudinal study of antioxidant and behavioral enrichment in canines

Studies in humans suggest that lifestyle factors can have a beneficial impact on the risk for developing cognitive decline and dementia with age. There is growing evidence that maintaining a physically and intellectually active lifestyle can positively impact cognitive ability in older individuals. Dietary factors, such as the intake of antioxidants, may also prevent age-related cognitive decline. However, studies in humans are challenging; many variables cannot be controlled, making it difficult for researchers to determine the exact types and quantities of enrichment and dietary factors necessary for positive effects on cognition. Studies in animal models of human aging allow researchers to precisely control such variables, and can be used to assess the mechanisms and molecular pathways underlying any positive effects. Here we review the results of an intervention study using a canine model of human aging. The study was unique in that it compared the effects of dietary antioxidant supplementation alone and in combination with behavioral enrichment. We found that both interventions lead to improvements in cognitive ability in aged dogs; however, combining the treatments preserved cognition to a greater extent than either treatment alone. Overall, the results suggest that antioxidant supplementation and behavioral enrichment target separate yet complementary molecular pathways to improve cognition, and support the idea that combinations of treatments to improve cognition and slow brain aging will produce greater benefits than single interventions.

Beta-amyloid cortical deposits are accompanied by the loss of serotonergic neurons in the dog

Dogs may naturally suffer an age-related cognitive impairment that has aroused a great deal of interest, even beyond the field of the veterinary clinic. This canine senile dementia reproduces several key aspects of Alzheimer's disease (AD), including the presence of beta-amyloid (A beta) deposits in the cerebral cortex, neurodegeneration, and learning and memory impairments. In the present study, we have used unbiased stereological procedures to estimate the number of the dorsal and median raphe nuclei (DRN and MRN, respectively) serotonergic neurons immunolabeled with an anti-tryptophan hydroxylase (TrH) monoclonal antibody in young and aged dogs without A beta cortical deposits and in aged dogs with A beta cortical deposits. The estimated total number of TrH-labeled neurons (mean +/- SD) was 94,790 +/- 26,341 for the DRN and 40,404 +/- 8,692 for the MRN. The statistical analyses revealed that aged dogs with A beta cortical pathology had 33% fewer serotonergic neurons in the DRN and MRN than aged dogs without A beta cortical deposits (108,043 +/- 18,800 vs. 162,242 +/- 39,942, respectively; P = 0.01). In contrast, no significant variations were found between young and aged dogs without A beta cortical deposits. These results suggest that degeneration of the serotonergic neurons could be involved in the cognitive damage that accompanies A beta cortical pathology in the dog and reinforce the use of the canine model for exploring the potential mechanisms linking the cortical A beta pathology and serotonergic neurodegeneration that occurs during the course of AD.

Age-related modifications of egr1 expression and ubiquitin-proteasome components in pet dog hippocampus

In this paper we examined the impact of age on cognitive functions and the age-related modifications of egr1 expression, an inducible transcription factor with a confirmed role in synaptic plasticity and regulation of the proteasome activity, on pet dogs. Additionally, we examined the age-related changes of some elements of the ubiquitin-proteasome system, which is the apparatus that prevents the intracellular accumulation of abnormal proteins. The results of behavioral analysis revealed that old/senior dogs (9-16-year-old) had impaired cognitive performance compared to young/middle-aged dogs (2-8-year-old) in the Reversal Learning task. Taken togheter, the results (age-related decline of Psmd4, Psmb8, CHIP, and egr1 expression; increase of Psmb9 and Hsp90 expression) suggest that the activity of the ubiquitin-proteasome system in the dog hippocampus is a multi-step process, in which abnormal proteins destined for degradation are recognized and destroyed, and shows an age-related decline. The consequent failure of the "protein quality control system" might have detrimental effects on cell physiology and lead to a progressive impairment of cognitive functions.

Use of copper and insulin-resistance to accelerate cognitive deficits and synaptic protein loss in a rat Abeta-infusion Alzheimer's disease model

The rat amyloid-beta (Abeta) intracerebroventricular infusion can model aspects of Alzheimer's disease (AD) and has predicted efficacy of therapies such as ibuprofen and curcumin in transgenic mouse models. High density lipoprotein (HDL), a normal plasma carrier of Abeta, is used to attenuate Abeta aggregation within the pump, causing Abeta-dependent toxicity and cognitive deficits within 3 months. Our goal was to identify factors that might accelerate onset of Abeta-dependent deficits to improve efficiency and cost-effectiveness of model. We focused on: 1) optimizing HDL-Abeta preparation for maximal toxicity; 2) evaluating the role of copper, a factor typically in water that can impact oligomer stability; and 3) determining impact of insulin resistance (type II diabetes), a risk factor for AD. In vitro studies were performed to determine doses of copper and methods of Abeta-HDL preparation that maximized toxicity. These preparations when infused resulted in earlier onset of cognitive deficits within 6 weeks post-infusion. Induction of insulin resistance did not exacerbate Abeta-dependent cognitive deficits, but did exacerbate synaptic protein loss. In summary, the newly described in vivo infusion model may be useful cost-effective method for screening for new therapeutic drugs for AD.

Rhinal and dorsolateral prefrontal cortex lesions produce selective impairments in object and spatial learning and memory in canines

To examine the effects of rhinal and dorsolateral prefrontal cortex lesions on object and spatial recognition memory in canines, we used a protocol in which both an object (delayed nonmatching to sample, or DNMS) and a spatial (delayed nonmatching to position or DNMP) recognition task were administered daily. The tasks used similar procedures such that only the type of stimulus information to be remembered differed. Rhinal cortex (RC) lesions produced a selective deficit on the DNMS task, both in retention of the task rules at short delays and in object recognition memory. By contrast, performance on the DNMP task remained intact at both short and long delay intervals in RC animals. Subjects who received dorsolateral prefrontal cortex (dlPFC) lesions were impaired on a spatial task at a short, 5-second delay, suggesting disrupted retention of the general task rules; however, this impairment was transient, and long-term spatial memory performance was unaffected in dlPFC subjects. The present results provide support for the involvement of the RC in object, but not visuospatial, processing and recognition memory, whereas the dlPFC appears to mediate retention of a nonmatching rule. These findings support theories of functional specialization within the medial temporal lobe and frontal cortex and suggest that rhinal and dorsolateral prefrontal cortices in canines are functionally similar to analogous regions in other mammals.

Oxidative damage and cognitive dysfunction: antioxidant treatments to promote healthy brain aging

Oxidative damage in the brain may lead to cognitive impairments in aged humans. Further, in age-associated neurodegenerative disease, oxidative damage may be exacerbated and associated with additional neuropathology. Epidemiological studies in humans show both positive and negative effects of the use of antioxidant supplements on healthy cognitive aging and on the risk of developing Alzheimer disease (AD). This contrasts with consistent behavioral improvements in aged rodent models. In a higher mammalian model system that naturally accumulates human-type pathology and cognitive decline (aged dogs), an antioxidant enriched diet leads to rapid learning improvements, memory improvements after prolonged treatment and cognitive maintenance. Cognitive benefits can be further enhanced by the addition of behavioral enrichment. In the brains of aged treated dogs, oxidative damage is reduced and there is some evidence of reduced AD-like neuropathology. In combination, antioxidants may be beneficial for promoting healthy brain aging and reducing the risk of neurodegenerative disease.

Complementary Distributions of Amyloid-β and Neprilysin in the Brains of Dogs and Cats

Neprilysin is an amyloid-β-degrading enzyme localized in the brain parenchyma. The involvement of neprilysin in the pathogenesis of Alzheimer's disease has recently received much attention. We examined the localization of neprilysin and amyloid-β, as well as the activity of neprilysin, in the brains of dogs and cats of various ages to clarify the relationship between neprilysin activity and amyloid-β deposition. The distribution of neprilysin was almost identical in dogs and cats, being high in the striatum, globus pallidus, and substantia nigra, but very low in the cerebral cortex. The white matter and hippocampus were negative. Neprilysin activity in the brain regions in dogs and cats was ranked from high to low as follows: thalamus/striatum > cerebral cortex > hippocampus > white matter. Amyloid-β deposition was first detected at 7 and 10 years of age in dogs and cats, respectively, and both the quantity and frequency of deposition increased with age. In both species, amyloid-β deposition appeared in the cerebral cortex and the hippocampus. In summary, the localization of neprilysin and neprilysin activity, and that of amyloid-β, were complementary in the brains of dogs and cats.

Effect of aging on neurogenesis in the canine brain

An age-dependent decline in hippocampal neurogenesis has been reported in laboratory rodents. Environmental enrichment proved to be a strong trigger of neurogenesis in young and aged laboratory rodents, which are generally kept in facilities with a paucity of environmental stimuli. These data raise the question whether an age-dependent decline in hippocampal cell proliferation and neurogenesis can also be observed in individuals exposed to diversified and varying surroundings. Therefore, we determined rates of canine hippocampal neurogenesis using post-mortem tissue from 37 nonlaboratory dogs that were exposed to a variety of environmental conditions throughout their life. Expression of the neuronal progenitor cell marker doublecortin clearly correlated with age. The analysis of doublecortin-labeled cells in dogs aged > 133 months indicated a 96% drop in the aged canine brain as compared to young adults. Expression of the proliferation marker Ki-67 in the subgranular zone decreased until dogs were aged 85-132 months. In the aging canine brain amyloid-beta peptide deposits have been described that might resemble an early pathophysiological change in the course of human Alzheimer's disease. Comparison of Ki-67 and doublecortin expression in canine brain tissue with or without diffuse plaques revealed no differences. The data indicate that occurrence of diffuse plaques in the aging brain is not sufficient to trigger enhanced proliferation or enhanced neurogenesis such as described in human Alzheimer's disease. In addition, this study gives first proof that an age-dependent decline also dominates hippocampal neurogenesis rates in individuals living in diversified environments.

Redox proteomics studies of in vivo amyloid beta-peptide animal models of Alzheimer's disease: Insight into the role of oxidative stress

Alzheimer's disease (AD) is an age-related neurodegenerative disease. AD is characterized by the presence of senile plaques, neurofibrillary tangles, and synaptic loss. Amyloid β-peptide (Aβ), a component of senile plaques, has been proposed to play an important role in oxidative stress in AD brain and could be one of the key factors in the pathogenesis of AD. In the present review, we discuss some of the AD animal models that express Aβ, and compare the proteomics-identified oxidatively modified proteins between AD brain and those of Aβ models. Such a comparison would allow better understanding of the role of Aβ in AD pathogenesis thereby helping in developing potential therapeutics to treat or delay AD.

A two-year study with fibrillar beta-amyloid (Abeta) immunization in aged canines: effects on cognitive function and brain Abeta

Aged canines (dogs) accumulate human-type beta-amyloid (Abeta) in diffuse plaques in the brain with parallel declines in cognitive function. We hypothesized that reducing Abeta in a therapeutic treatment study of aged dogs with preexisting Abeta pathology and cognitive deficits would lead to cognitive improvements. To test this hypothesis, we immunized aged beagles (8.4-12.4 years) with fibrillar Abeta(1-42) formulated with aluminum salt (Alum) for 2.4 years (25 vaccinations). Cognitive testing during this time revealed no improvement in measures of learning, spatial attention, or spatial memory. After extended treatment (22 vaccinations), we observed maintenance of prefrontal-dependent reversal learning ability. In the brain, levels of soluble and insoluble Abeta(1-40) and Abeta(1-42) and the extent of diffuse plaque accumulation was significantly decreased in several cortical regions, with preferential reductions in the prefrontal cortex, which is associated with a maintenance of cognition. However, the amount of soluble oligomers remained unchanged. The extent of prefrontal Abeta was correlated with frontal function and serum anti-Abeta antibody titers. Thus, reducing total Abeta may be of limited therapeutic benefit to recovery of cognitive decline in a higher mammalian model of human brain aging and disease. Immunizing animals before extensive Abeta deposition and cognitive decline to prevent oligomeric or fibrillar Abeta formation may have a greater impact on cognition and also more directly evaluate the role of Abeta on cognition in canines. Alternatively, clearing preexisting Abeta from the brain in a treatment study may be more efficacious for cognition if combined with a second intervention that restores neuron health.

Improvement of short-term memory performance in aged beagles by a nutraceutical supplement containing phosphatidylserine, Ginkgo biloba, vitamin E, and pyridoxine

Aged dogs demonstrate cognitive decline that is linked to brain aging. The purpose of the present study was to examine if a commercially available nutraceutical supplement that may be neuroprotective and contains phosphatidylserine, Ginkgo biloba, vitamin E, and pyridoxine could improve cognitive function in aged beagles. Nine aged beagles were tested on performance on a delayed-non-matching-to-position task, which is a neuropsychological test of short-term visuospatial memory. All subjects were tested on 5 baseline sessions; then, to assess the supplement, a crossover design was used in which 1 group received the supplement and the other a control substance in the 1st phase, with treatment conditions being reversed in the 2nd phase. Performance accuracy was significantly improved in supplemented dogs compared with control dogs and the effect was long lasting. These findings suggest that the nutraceutical supplement can improve memory in aged dogs.

Implications of age and diet on canine cerebral cortex transcription

Mechanisms contributing to age-related cognitive decline are poorly defined. Thus, we used canine microarrays to compare gene expression profiles of brain tissue from geriatric and young adult dogs. Cerebral cortex samples were collected from six geriatric (12-year old) and six young adult (1-year old) female beagles after being fed one of two diets (animal protein-based versus plant-protein based) for 12 months. RNA samples were hybridized to Affymetrix GeneChip Canine Genome Arrays. Statistical analyses indicated that the age had the greatest impact on gene expression, with 963 transcripts differentially expressed in geriatric dogs. Although not as robust as age, diet affected mRNA abundance of 140 transcripts. As demonstrated in aged rodents and humans, geriatric dogs had increased expression of genes associated with inflammation, stress response, and calcium homeostasis and decreased expression of genes associated with neuropeptide signaling and synaptic transmission. In addition to its existing strengths, availability of gene sequence information and commercial microarrays make the canine a powerful model for studying the effects of aging on cognitive function.

Oxidative stress, aging, and central nervous system disease in the canine model of human brain aging

Decline in cognitive functions that accompany aging in dogs may have a biologic basis, and many of the disorders associated with aging in dogs may be mitigated through dietary modifications that incorporate specific nutraceuticals. Based on previous research and the results of laboratory and clinical studies, antioxidants may be one class of nutraceutical that provides benefits to aged dogs. Brains of aged dogs accumulate oxidative damage to proteins and lipids, which may lead to dysfunction of neuronal cells. The production of free radicals and lack of increase in compensatory antioxidant enzymes may lead to detrimental modifications to important macromolecules within neurons. Reducing oxidative damage through food ingredients rich in a broad spectrum of antioxidants significantly improves, or slows the decline of, learning and memory in aged dogs.

Roles of amyloid beta-peptide-associated oxidative stress and brain protein modifications in the pathogenesis of Alzheimer's disease and mild cognitive impairment

Oxidative stress has been implicated to play a crucial role in the pathogenesis of a number of diseases, including neurodegenerative disorders, cancer, and ischemia, just to name a few. Alzheimer disease (AD) is an age-related neurodegenerative disorder that is recognized as the most common form of dementia. AD is histopathologically characterized by the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles, the presence of oligomers of amyloid beta-peptide (Abeta), and synapse loss. In this review we discuss the role of Abeta in the pathogenesis of AD and also the use of redox proteomics to identify oxidatively modified brain proteins in AD and mild cognitive impairment. In addition, redox proteomics studies in in vivo models of AD centered around human Abeta(1-42) are discussed.

Region specific neuron loss in the aged canine hippocampus is reduced by enrichment

Neuron loss within the hippocampus and entorhinal cortex occurs as a function of age in humans. We first tested the hypothesis that neuron loss occurs in the aged dog. The total unilateral number of neurons in the canine entorhinal cortex and subdivisions of the hippocampus from the left hemisphere were estimated using the optical fractionator. The brains from 5 old (13.0-15.0 years old) and 5 young (3.4-4.5 years old) beagle dogs were analyzed. The hilus of the hippocampus showed a significant loss of neurons (approximately 30%) in the aged dog brain compared to young. Differences were not detected in the remaining hippocampal subfields and entorhinal cortex. We further tested the hypothesis that an antioxidant fortified food or behavioral enrichment would reduce the age-related loss of hilar neurons. Behaviorally enriched aged dogs had more neurons in the hilus (approximately 18%) compared to aged controls. These results suggest that the aged canine hippocampus in the left hemisphere shows selective neuron loss and that behavioral enrichment may reduce this loss.

Therapeutic Options for Cognitive Decline in Senior Pets

Many treatment options are now available for pets with age-related cognitive dysfunction, including drugs, nutritional supplements, and diets. This article describes the theory, evidence of efficacy, and potential neuroprotective effects of products used to treat cognitive dysfunction. Cognitive dysfunction is a diagnosis of exclusion, because many painful conditions and health problems may present with similar signs. Practitioners must, therefore, actively question owners of senior pets in order to diagnose cognitive dysfunction and to assess the pet’s general health and well-being.

Voxel based versus region of interest analysis in diffusion tensor imaging of neurodevelopment

There are two main methods of quantitative analysis in diffusion tensor imaging (DTI) studies: manual region of interest (ROI) and automated voxel based. The purpose of this study is to compare the results of each of these methods applied to the same data set. Linear correlative analysis was performed for mean diffusivity (Trace/3 ADC) and for fractional anisotropy (FA) versus age within 8-12 years (N = 32) and within 21-27 years (N = 28), as well as a group comparison. SPM analysis identified more structures changing with age, partly due to the limited regions measured with ROI analysis. In general, ROI and voxel-based analysis methods produced comparable results for widespread reductions of Trace/3 ADC and increases of FA with age, particularly for group comparison. The discrepancies (i.e., missed regions) were likely related to problems of spatial normalization for SPM analysis, and masking localized changes by averaging all the voxels within a region of interest for ROI analysis. These two analysis methods for DTI offer complementary results, but neither one yields the complete story of neurodevelopment.

Proteomic identification of brain proteins in the canine model of human aging following a long-term treatment with antioxidants and a program of behavioral enrichment: relevance to Alzheimer's disease

Aging and age-related disorders such as Alzheimer's disease (AD) are usually accompanied by oxidative stress as one of the main mechanisms contributing to neurodegeneration and cognitive decline. Aging canines develop cognitive dysfunction and neuropathology similar to those seen in humans, and the use of antioxidants results in reductions in oxidative damage and in improvement in cognitive function in this canine model of human aging. In the present study, the effect of a long-term treatment with an antioxidant-fortified diet and a program of behavioral enrichment on oxidative damage was studied in aged canines. To identify the neurobiological mechanisms underlying these treatment effects, the parietal cortex from 23 beagle dogs (8.1-12.4 years) were treated for 2.8 years in one of four treatment groups: i.e., control food-control behavioral enrichment (CC); control food-behavioral enrichment (CE); antioxidant food-control behavioral enrichment (CA); enriched environment-antioxidant-fortified food (EA). We analyzed the levels of the oxidative stress biomarkers, i.e., protein carbonyls, 3-nitrotyrosine (3-NT), and the lipid peroxidation product, 4-hydroxynonenal (HNE), and observed a decrease in their levels on all treatments when compared to control, with the most significant effects found in the combined treatment, EA. Since EA treatment was most effective, we also carried out a comparative proteomics study to identify specific brain proteins that were differentially expressed and used a parallel redox proteomics approach to identify specific brain proteins that were less oxidized following EA. The specific protein carbonyl levels of glutamate dehydrogenase [NAD (P)], glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alpha-enolase, neurofilament triplet L protein, glutathione-S-transferase (GST) and fascin actin bundling protein were significantly reduced in brain of EA-treated dogs compared to control. We also observed significant increases in expression of Cu/Zn superoxide dismutase, fructose-bisphosphate aldolase C, creatine kinase, glutamate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase. The increased expression of these proteins and in particular Cu/Zn SOD correlated with improved cognitive function. In addition, there was a significant increase in the enzymatic activities of glutathione-S-transferase (GST) and total superoxide dismutase (SOD), and significant increase in the protein levels of heme oxygenase (HO-1) in EA treated dogs compared to control. These findings suggest that the combined treatment reduces the levels of oxidative damage and improves the antioxidant reserve systems in the aging canine brain, and may contribute to improvements in learning and memory. These observations provide insights into a possible neurobiological mechanism underlying the effects of the combined treatment. These results support the combination treatments as a possible therapeutic approach that could be translated to the aging human population who are at risk for age-related neurodegenerative disorders, including Alzheimer's disease.

Inflammatory processes in the aging mouse brain: participation of dendritic cells and T-cells

Increased inflammatory activity accompanies normal brain aging. Whereas local glial cell activation, upregulation of cytokines and transcriptional alterations of inflammatory factors are well-documented components of this complex process, it is unclear whether blood-derived leukocytes also contribute to the age-related changes. The present study of normal mouse brain applied single and double immunohistochemistry to reveal for the first time that dendritic cells (DCs) and T-cells are important components of the general increased inflammatory state, which was documented by upregulation of reactive astrocytes and microglia. B-cells and mast cells do not contribute to this inflammatory response. Dendritic cells and T-cells appeared at about 12 months of age and their number increased further during aging. In 24-month-old animals a dense network of DCs interspersed with T-cells pervaded brain areas where substantial histopathological changes and a volumetric decrease have been reported. All CD11c(+)-DCs displayed the typical dendritic shape and expressed the myeloid specific integrin CD11b. Some of the DCs were also CD205- or MIDC8-immunoreactive and expressed the cathepsins S and X. The emergence and prolonged presence of leukocytes might indicate a crucial role of these cells in local, age-related immune responses in the brain.

Regional white matter and neuropsychological functioning across the adult lifespan

BACKGROUND

The current study utilized magnetic resonance imaging (MRI) to more fully elucidate the relationship among age, regional white matter, and neuropsychological functioning.

METHODS

One hundred ninety-nine neurologically healthy adults received MRI and standardized neuropsychological assessment. MR images were spatially normalized and segmented by tissue type; relative white matter values in each of the four cerebral lobes in each hemisphere were computed. Subjects were divided into Younger (ages 21-30), Middle (ages 31-54), and Older (ages 55-79) age groups.

RESULTS

The Older group had significantly less overall relative white matter than the Middle group, who had significantly less overall relative white matter than the Younger participants (F (2, 193) = 5.42, p = 0.005). Differences in frontal lobe white matter were of largest magnitude, followed by temporal lobe (F (6, 579) = 3.32, p = 0.003). Age and frontal and temporal lobe white matter were primarily associated with performance on neuropsychological tests of executive functioning and memory. Mediational analysis suggested that frontal lobe white matter mediated the relationship between age and performance on tasks of executive functioning and memory.

CONCLUSIONS

The results confirm age-associated decline in frontal and temporal white matter, and age-related cognitive decline in several domains. Decline in neuropsychological functioning is, in part, mediated by a relative age-related reduction in frontal white matter.

Neuroprotective effects of cognitive enrichment

Cognitive enrichment early in life, as indicated by level of education, complexity of work environment or nature of leisure activities, appears to protect against the development of age-associated cognitive decline and also dementia. These effects are more robust for measures of crystallized intelligence than for measures of fluid intelligence and depend on the ability of the brain to compensate for pathological changes associated with aging. This compensatory ability is referred to as cognitive reserve. The cognitive reserve hypothesis suggests that cognitive enrichment promotes utilization of available functions. Alternatively, late life cognitive changes in cognition may be linked to a factor, such as cholinergic dysfunction, that is also present early in life and contributes to the reduced levels of early life cognitive enrichment. Beneficial effects of environmental enrichment early in life have also been observed in rodents and primates. Research with rodents indicates that these changes have structural correlates, which likely include increased synapses in specific brain regions. Dogs also show age-dependent cognitive decline, and both longitudinal and cross-sectional studies indicate that this decline can be attenuated by cognitive enrichment. Furthermore, cognitive enrichment has differential effects, improving some functions more than others. From a neurobiological perspective, behavioral enrichment in the dog may act to promote neurogenesis later in life. This can be distinguished from nutritional interventions with antioxidants, which appear to attenuate the development of neuropathology. These results suggest that a combination of behavioral and nutritional or pharmacological interventions may be optimal for reducing the rate of age-dependent cognitive decline.

In vivo MRI and histological evaluation of brain atrophy in APP/PS1 transgenic mice

Regional cerebral atrophy was evaluated in APP/PS1 mice harboring mutated transgenes linked to familial Alzheimer's disease, using complementary methods. In vivo high resolution MRI was selected for measurements of brain atrophy and associated cerebrospinal fluid dilation; histological analysis was performed to reveal localized atrophies and to evaluate amyloid burden. Young APP/PS1 mice examined at a pre-amyloid stage (10 weeks) showed disruption in development (reduced intracranial and brain volumes). Comparison of young and old (24 months) mice, indicated that both APP/PS1 and control brains endure growth during adulthood. Aged APP/PS1 animals showed a moderate although significant global brain atrophy and a dilation of CSF space in posterior brain regions. The locus of this atrophy was identified in the midbrain area and not, as expected, at isocortical/hippocampal levels. Atrophy was also detected in fiber tracts. The severity of brain atrophy in old APP/PS1 mice was not correlated with the extent of cerebral amyloidosis. The relevance of current transgenic mouse models for the study of brain atrophy related to Alzheimer's disease is discussed.

Cognitive disturbances in old dogs suffering from the canine counterpart of Alzheimer's disease

In geriatric dogs, Alzheimer-like behavior is frequently observed. This behavior has been classified by several authors using questionnaires and a correlation has been described between cognitive dysfunctions and Alzheimer-like pathology. In the present study, cognitive performance was correlated with brain pathology for 30 dogs of varying ages. Within these animals, two age-matched groups of old dogs with and without behavioral changes were compared. The behavioral changes were analyzed and scored with questionnaires and necropsy was performed to rule out any other cause for changed behavior. Measurements, (immuno)-histochemical staining and fluorescence microscopy were used to detect cortex atrophy, amyloid, rest-products of oxidative damage, demyelination and accumulations of macrophages in the brains of these dogs. Spearman rank correlation coefficients (r) were calculated and adjusted according to Bonferonni. In the whole group (young to very old dogs), the age of the animal showed a significant correlation with various behavioral changes (r = 0.7 to 0.9, P < 0.01). The dementia score correlated significantly (r = 0.6 to 0.8, P < 0.01) with all the brain lesions studied, except one, i.e. demyelination (r = -0.4, P > 0.05). These results suggest that a questionnaire can be used to diagnose Alzheimer-like changes in canine practice. Oxidative damage on a cellular and a nuclear level plays an important role in behavior changes.

Application of an automated voxel-based morphometry technique to assess regional gray and white matter brain atrophy in a canine model of aging

In recent years, voxel-based morphometry (VBM) has emerged as a technique to examine regional brain changes associated with normal and pathological aging. Despite its popularity in studies of human aging, application of VBM to animal models of brain aging is rare. In the present study, VBM techniques were developed to validate earlier region of interest (ROI) measures of brain aging in the dog and to provide a more comprehensive analysis of local changes in a canine model of brain aging. Consistent with previous findings, frontal lobe atrophy increased with age, most notably in aged male dogs. Age-related gray matter reductions were also observed in parietal and temporal lobes, thalamus, cerebellum, and brainstem. Temporal lobe atrophy was particularly prominent in old females. A number of age-related changes in white matter not previously explored in the dog were also identified with VBM. Specifically, aged males exhibited greater decreases in the internal capsula and cranial nerve bundles compared to decreased volumes in the alveus of the hippocampus in old female dogs. Together, the present results indicate that application of VBM techniques in a canine model of aging yields more comprehensive information regarding topographical patterns of brain aging in male and female dogs than previously reported using traditional manual ROI methods.

MEASUREMENT OF INTERTHALAMIC ADHESION THICKNESS AS A CRITERIA FOR BRAIN ATROPHY IN DOGS WITH AND WITHOUT COGNITIVE DYSFUNCTION (DEMENTIA)

The criteria for brain atrophy in dogs have not yet been established, because of wide variation in the morphology of the ventricles and sulci of the brain depending on the breed and size. In this study, we examined the thickness of the interthalamic adhesion in a transverse magnetic resonance image to investigate normal, to examine the correlation with age, body weight, and breed, and to assess whether measurement would be a useful indicator of brain atrophy. The animals used in this study were of various breeds and weight, and had no identifiable intracranial lesion. They were divided into two groups: a normal group (0.6-15-year-old, n = 66) and a demented aging group (12-18-year-old, n = 12). The interthalamic adhesion thickness in both T1- and T2-weighted transverse images were measured in all dogs. The interthalamic adhesion thickness in the normal and demented groups was 6.79 +/- 0.70 and 3.82 +/- 0.79 mm, respectively. The interthalamic adhesion thickness in the demented group was significantly smaller. In an analysis of the correlation of interthalamic adhesion thickness with age and weight in normal dogs, significant negative and positive correlation was recognized, respectively. However, the strength of these correlations was low. These results suggest that interthalamic adhesion thickness may be a good parameter for evaluating brain atrophy in dogs with cognitive dysfunction.