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Cognitive dysfunction in older dogs and cats: the role of the veterinary nurse in screening
Abstract
Cognitive dysfunction is a progressive neurodegenerative disorder. It affects 14.2% of older dogs over 8 years of age. In cats, 28% aged 11 to 14 years develop one geriatric-onset behaviour problem. This increases to over 50% in cats 15 years of age and older. Detection of cognitive dysfunction in cats and dogs is by observation of clinical behavioural signs, often thought to be a normal part of ageing. Early recognition is crucial. Signs detected early are treatable or temporarily reversible.
This literature review focused on areas the veterinary nurse could influence in practice such as detection of behavioural signs and advice on diet, behaviour management and enrichment.
Results showed dietary and nutritional supplements as well as behavioural and environmental enrichment alongside medication can slow progression of cognitive dysfunction predominately in dogs. Regular screening of older pets and education of owners by veterinary nurses can help with early detection and referral to a veterinary surgeon. Future research should focus on further development of standardised, validated screening tools and management protocols.
Background: Veterinary professionals have seen a rise in geriatric patients suffering from canine cognitive dysfunction (CCD). Previous literature has supported the use of environmental enrichment therapies which have been considered to reduce the progression of cognitive decline in CCD. However, CCD is commonly undiagnosed within the companion dog population.
Aim: To determine whether owners of older dogs are able to notice behavioural changes, and in addition, explore knowledge around the term environmental enrichment which may help owners slow the progression of CCD through further education.
Method: The study involved quantitative research using a questionnaire with 11 questions. Data were subsequently statistically analysed. Of the participants 16 worked within a veterinary practice, 52 were customers visiting a pet shop and 39 respondents formed a web survey group predominantly of veterinary professionals.
Results: Owners of geriatric dogs working within a veterinary-related field were more likely to notice behavioural changes possibly associated with CCD compared with the average owner of a geriatric dog, and were also more likely to understand the term environmental enrichment.
Conclusion: This study informs the veterinary field that improved education strategies implemented within nurse clinics may help pet owners recognise behavioural indicators of CCD, and treatment recommendations may assist in slowing the progression of CCD in geriatric dogs.
Several cognitive tests have been developed to evaluate specific aspects of human and animal learning and memory. These tests have been used for early detection of cognitive deficits and to monitor the treatment of dogs with cognitive impairment. Thus, this article evaluated the feasibility of cognitive tests for use in canine neurology clinical routine and the suitability of the different tests to accomplish this aim. Fifteen healthy adult dogs were used for the cognitive tests of reward approach learning, object approach learning, object discrimination learning, reversal learning, delay non-matched to position, and delay non-matched to sample to assess different aspects of memory. No difference was observed between tests of delay non-matched to position (3.13 ± 2.23 days) and delay non-matched to sample (3.20 ± 2.40 days) (P = 0.944). However, dogs had greater difficulty in reversal learning (8.47 ± 2.61 days) than in object discrimination learning (4.60 ± 1.64 days) (P ≤ 0.001). Based on the tests performed, the delay non-matched to position test may be performed in clinical routine if the owner and the veterinarian have time available, because this test is sensitive to evaluate dogs with cognitive impairments, but requires approximately 10 days of training. Thus, elderly dogs are excellent experimental models to study pathological aging based on their similarities with some human brain diseases, such as Alzheimer disease.
Cognitive dysfunction syndrome is a major disease affecting old cats and is the consequence of severe and irreversible loss of brain cells and brain atrophy. The present study focused on the hypothesis that the optimal strategy for promoting successful brain ageing is to target risk factors associated with brain ageing and dementia. We used a nutritional strategy involving supplementation with a blend of nutrients (antioxidants, arginine, B vitamins and fish oil) to test this hypothesis. Middle-aged and old cats between 5·5 and 8·7 years of age were assigned to cognitively equivalent control or treatment groups based on prior cognitive experience and performance on baseline cognitive tests. The cats in the treatment group were maintained on a diet supplemented with the nutrient blend and the cats in the control group were maintained on the identical base diet without the additional supplementation. After an initial wash-in period, all cats were tested on a battery of cognitive test protocols. The cats fed the test diet showed significantly better performance on three of four test protocols: a protocol assessing egocentric learning, a protocol assessing discrimination and reversal learning and a protocol focused on acquisition of a spatial memory task. The results support the hypothesis that brain function of middle-aged and old cats can be improved by the nutrient blend that was selected to minimise or eliminate the risk factors associated with brain ageing and dementia.
Brain aging is a degenerative process manifest by impairment of cognitive function; although not all pets are affected at the same level, once cognitive decline begins it is generally a progressive disorder. Diagnosis of cognitive dysfunction syndrome (CDS) is based on recognition of behavioral signs and exclusion of other medical causes that might mimic CDS or complicate its diagnosis. Drugs, diets, and supplements are now available that might slow CDS progression by various mechanisms including reducing oxidative stress and inflammation or improving mitochondrial and neuronal function. Moreover, available therapeutics may provide some level of improvement in cognitive and clinical signs of CDS.
The present study focused on the hypothesis that dietary supplementation with medium-chain TAG (MCT) will improve cognitive function in aged dogs by providing the brain with energy in the form of ketones. Aged Beagle dogs were subjected to a baseline battery of cognitive tests, which were used to establish cognitively equivalent control or treatment groups. The dogs in the treatment group were maintained on a diet supplemented with 5.5 % MCT. After an initial wash-in period, all the dogs were tested with a battery of cognitive test protocols, which assessed sequentially landmark discrimination learning ability, egocentric visuospatial function and attention. The groups were maintained on the diets for 8 months. The MCT-supplemented group showed significantly better performance in most of the test protocols than the control group. The group differences also varied as a function of task difficulty, with the more difficult task showing greater supplementation effects than the easier tasks. The group given the MCT supplement showed significantly elevated levels of beta-hydroxybutyrate, a ketone body. These results indicate, first, that long-term supplementation with MCT can have cognition-improving effects, and second, that MCT supplementation increases circulating levels of ketones. The results support the hypothesis that brain function of aged dogs can be improved by MCT supplementation, which provides the brain with an alternative energy source.
Most veterinarians hold a 'pediatric' rather than 'garage mechanic' view of their function. In recent years, sophisticated medical modalities have allowed veterinarians to keep animals alive, and increased value of companion animals in society has increased demand for such treatment. But whereas humans can choose to trade current suffering for extended life, animals seem to lack the cognitive apparatus required to do so. Thus, veterinarians must guard against keeping a suffering animal alive for too long. Clients may be emotionally tied to the animal and blind to its suffering. Part of the veterinarian's role, therefore, is to lead the client to 'recollect' quality of life issues. A second major role for the veterinarian in treating geriatric or chronically ill animals is control of pain and distress. Unfortunately, pain and distress have historically been neglected in both human and veterinary medicine for ideological reasons. It is ethically necessary to transcend this ideology which leads to both bad medicine and bad ethics.
As animals age, behaviour changes may be the first indication of declining health and welfare. This is especially true for some of the more common problems associated with ageing, such as pain, sensory decline and cognitive dysfunction syndrome (CDS). Cognitive dysfunction syndrome is the term used to describe the behavioural changes and learning and memory impairment seen secondary to age-related degeneration of the brain. Using the recommendations highlighted within this article it may prove possible to reduce anxiety levels in dogs suffering from CDS as well as provide support for owners in dealing with this complex and often distressing disease of their ageing companion.
Few tests have been developed to test the cognitive and motor capabilities of domestic cats, in spite of the suitability of cats for specific studies of neuroanatomy, infectious diseases, development, aging, and behavior. The present study evaluated a T-maze apparatus as a sensitive and reliable measure of cognition and motor function of cats. Eighteen purpose-bred, specific-pathogen-free, male, neutered domestic shorthair cats (Felis catus), 1-2 years of age, were trained and tested to a T-maze protocol using food rewards. The test protocol consisted of positional discrimination training (left arm or right arm) to criterion followed by two discrimination reversal tests. The two reversal tests documented the ability of the subjects to respond to a new reward location, and switch arms of the T-maze. Data were collected on side preference, number of correct responses, and latency of responses by the subjects. Aided by a customized computer program (CanCog Technologies), data were recorded electronically as each cat progressed from the start box to the reward arm. The protocol facilitated rapid training to a high and consistent level of performance during the discrimination training. This learning was associated with a decrease in the latency to traverse the maze to a mean of 4.80 ± 0.87 s indicating strong motivation and consistent performance. When the rewarded side was reversed in the test phase, cats required more trials to reach criterion, as expected, but again showed reliable learning. The latency to reward in the first session of reversal increased 86% from the first to the last trial indicating that it may provide a useful index of cognitive processing. Latencies subsequently decreased as the new reversal paradigm was learned. This paradigm provides a relatively rapid and reliable test of cognitive motor performance that can be used in various settings for evaluation of feline cognitive and motor function.
The average age of the companion animal is increasing owing to advances in medicine, diagnostics, surgery and nutrition. Our pet populations are living longer and healthier lives with the average lifespan of a dog increasing by 70% since the 1930s (Garred, 20139.
GARRED, E. (2013) Aging canines: why blind, deaf and stinky breath need not apply to all. Veterinary Nursing Times. 13 (Aug). p. 10–11.View all references). As a result, veterinary professionals are required to spend an increasing amount of clinical time caring for an ageing pet population.It is widely known that frequent health checks are beneficial to patient health, allowing for identification of health-related issues as well as client education. Geriatric patients are not an exception to this rule. In fact it has been demonstrated that they are part of the patient demographic who may benefit most from frequent health screening.This article looks at the role of senior wellness clinics in the practical application of pet geriatric care.
The term cognitive dysfunction syndrome (CDS) has been used to refer to the changes of behavior related to aging with cognitive skills deterioration, that do not stem completely from medical conditions and that are a consequence of a degenerative process of the central nervous system. It is known that the CDS in dogs is caused by the physical and chemical changes that take place in the brain due to aging. The aim of this paper is to present a clinical case of CDS which was clinically diagnosed and then confirmed by necropsy at the veterinary hospital of the National Autonomous University of Mexico.
Dogs exhibit age-dependent losses in learning and memory as well as a progressive accumulation of neuropathology that parallels that observed in normal human aging and early Alzheimer’s disease. These deficits have been extensively studied using a number of standard cognitive tasks in the laboratory; however, appropriate tools for their assessment in veterinary clinics are still lacking. The aim of this study was to evaluate the effect of age and the severity of cognitive dysfunction syndrome (CDS) on two simple tests conducted in a clinical setting. A food searching (FS) task and a problem-solving (PS) task were administered to young (1–4 years, n = 9), middle-aged (5–8 years, n = 10), cognitively unimpaired aged (⩾9 years, n = 31), and cognitively impaired aged (⩾9 years, n = 37) dogs. Cognitive status was classified using an owner-based questionnaire, and in the impaired group, dogs were categorized as having either mild or severe CDS.
During the FS task, younger dogs (<9 years) were able to locate the food more quickly and with more success than the aged groups (⩾9 years). Dogs with severe CDS exhibited poorer performance than those with mild CDS or their healthy counterparts. In the PS task, younger dogs performed better than the aged dogs in obtaining food, but there were no differences related to CDS severity. The FS task might help to better characterize cognitively affected dogs in the clinical setting than the PS task. These and similar tasks require further investigations in the field.
A spatial learning task was used to examine cognitive function in 36 cats (1.0–15.1 years of age), with a control for motor function. No significant age-related decline in cognitive function was found. Initial selection of 75 cats showed no significant age differences between young (0–3 years), adult (3.1–8 years), senior (8.1–12 years) and geriatric cats (12.1–15.1 years) locating food rewards in a holeboard box. Consequently, the senior and geriatric groups were combined because of a concern that age effects may not be seen in the 8–12-year-old cats. Differences between these three age groups of cats to learn the position of three food rewards in an array of 30 otherwise empty (food-scented) positions were non-significant. Differences between age groups remained non-significant for retrieval of rewards from these three positions even when masked with a tissue paper cover. There was no significant effect of age on speed of reaching each criterion. Although the total number of errors was similar, there was a significantly increased proportion of working memory errors (when the cat returned to a previously baited position) and decreased proportion of reference memory errors (when the cat put a nose or paw in an empty position) with increasing age. There was no effect of age on motor function, with success in a plank-crossing test related only to plank width. These findings support previous work suggesting that the cat differs from other species in the way in which it demonstrates age-related declines in cognitive function. Further studies using different testing methodologies are required to assess other cognitive functions that may decline with age.
Canine cognitive dysfunction (CCD) is a clinical condition, which impacts significantly on the lives of elderly dogs and their owners. It is hypothesised that nutritional supplementation can be used in the management of the condition and this trial was designed to investigate the therapeutic effects of a specific supplement when compared to a placebo. The trial was conducted in a clinical context and involved 20 UK veterinary practices, giving geographical spread across the country. The duration of the trial was 56 days, including a baseline period of 7 days and a post trial period of 7 days. There was a significant difference between the treated and the placebo groups in relation to improvement in their scores for disorientation, changes in interaction and house soiling behaviour at day 21, day 28 and day 42. These results support the clinical practice of nutritional supplementation as a valuable component of the therapeutic approach in cases of canine cognitive dysfunction.
Canine cognitive dysfunction (CCD) is a neurodegenerative condition affecting geriatric dogs and sharing several characteristics with human Alzheimer's disease (AD). CCD manifests as alterations of behavioral patterns and daily routines. Clinical signs are associated with neurodegenerative changes (eg, cortical atrophy and amyloid-beta deposits).
To investigate clinical characteristics, survival, and risk factors with CCD. Vitamin E was investigated as a potential marker of CCD.
Ninety-four dogs >8 years of age were investigated with a validated CCD questionnaire and allocated to CCD, borderline CCD (b-CCD) and non-CCD groups. The dogs were included in 2008–2009 and followed up in an observational study until follow-up in 2012.
Four key clinical signs dominated in dogs with CCD: sleeping during the day and restless at night, decreased interaction, disorientation at home, and anxiety. A number of borderline CCD cases developed into CCD over time indicating that a prodromal stage of CCD may exist. CCD did not influence survival negatively. Small breeds did not show better survival than large breeds (P = .055) and there was no difference between sexes (P = .99).
A few key questions addressing sleep-wake cycle, interaction, and signs of confusion and anxiety can be used as a clinical marker of CCD. Special attention should be paid to anxiety in dogs with CCD because it may be especially stressful to both dog and owner. Dogs with CCD seem to have a good chance of living a full lifespan if supported by the veterinarian and the owner.
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.
Cognitive processes such as perception, learning, memory and decision making play an important role in mate choice, foraging and many other behaviours. In this review, I summarize a few key ideas about animal cognition developed in a recent book (Shettleworth 1998, Cognition, Evolution and Behaviour) and briefly review some areas in which interdisciplinary research on animal cognition is currently proving especially productive. Cognition, broadly defined, includes all ways in which animals take in information through the senses, process, retain and decide to act on it. Studying animal cognition does not entail any particular position on whether or to what degree animals are conscious. Neither does it entail rejecting behaviourism in that one of the greatest challenges in studing animal cognition is to formulate clear behavioural criteria for inferring specific mental processes. Tests of whether or not apparently goal-directed behaviour is controlled by a representation of its goal, episodic-like memory in birds, and deceptive behaviour in monkeys provide examples. Functional modelling has been integrated with analyses of cognitive mechanisms in a number of areas, including studies of communication, models of how predator learning and attention affect the evolution of conspicuous and cryptic prey, tests of the relationship betweeen ecological demands on spatial cognition and brain evolution, and in research on social learning. Rather than a ‘new field’ of cognitive ecology, such interdisciplinary research on animal cognition exemplifies a revival of interest in proximate mechanisms of behaviour.
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.
Increasing numbers of cats are living to become elderly and they commonly develop behavioral changes. The objectives of this article are to consider the possible causes and prevalence of behavioral problems in pet cats, to describe how cognitive dysfunction syndrome (CDS) typically presents, and how its diagnosis and management are often complicated by the concurrent presence of multiple interacting disease processes. The most frequently reported behavioral problems in old cats are loss of litter box training and crying out loudly at night. The most common causes of these problems are CDS, osteoarthritis, systemic hypertension (commonly secondary to chronic kidney disease or hyperthyroidism), hyperthyroidism (even without hypertension), deafness, and brain tumors. These conditions all occur frequently in older cats, many of which suffer from a number of concurrent interacting conditions. Owners and veterinary surgeons often mistake these for "normal aging changes," so many treatable conditions are neglected and go untreated. Almost one third of cats 11 to 14 years of age develop at least one geriatric-onset behavior problem that appears to relate to CDS, and this increases to over 50% for cats 15 years of age or older. For optimum management of elderly cats with behavioral problems, all interacting conditions need to be diagnosed and addressed concurrently with management for CDS.
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.
Canine cognitive dysfunction (CCD) is an age-related neurobehavioural syndrome which, although common, is severely under-diagnosed in community-based dogs. Using data from a large cross-sectional survey of older dogs (n=957), this study aimed to develop a clinical scale for assessing CCD. Data-driven analytical techniques were used to distil 27 significant behavioural items (previously identified as relevant to CCD) into an assessment tool with maximal cognito-behavioural breadth whilst maintaining clinical utility. The resulting CCD rating scale (CCDR) comprised 13 behavioural items, of which three were sensitive to the severity of the disease stage. When tested on an independent survey sample, the CCDR had an overall 98.9% diagnostic accuracy with a 77.8% positive predictive value and a 99.3% negative predictive value. Test-re-test reliability of the CCDR over 2months was also high (r=0.73, P<0.0001). In conjunction with veterinary assessment, the CCDR could be a valuable tool in research and clinical settings for both the assessment and longitudinal tracking of cognitive change.
Canine cognitive dysfunction (CCD) is a neurobehavioural syndrome affecting aged dogs. Using a large cross-sectional epidemiological study of older dogs, this study aimed to estimate the prevalence of CCD amongst community based dogs (mean age 11.67years; range 8-19.75) and to determine the rate of veterinary diagnosis amongst affected dogs. An 84-item questionnaire was used to obtain information across six behavioural domains. Of the eligible survey responses obtained (n=957) a randomly selected one-half (n=497) was used for this study. Using a provisional diagnosis based on 27 significant behavioural items, the prevalence rate of CCD was estimated to be 14.2%. This was in contrast with only 1.9% diagnosed with CCD by a veterinarian. There was an exponential increase in prevalence of CCD with age (R2=0.9435), but prevalence did not differ by breed size or between longevity groups. The prevalence rate of CCD reported here is consistent with previous findings, and further supports the contention that the majority of these dogs do not receive a formal diagnosis.
Background:
Cats are the most popular pet in the United States and much of Northern Europe. Although 78% of owners consider their cats to be family members, many cats, particularly seniors, do not receive appropriate preventive care. One of the main obstacles to owner compliance is the lack of a clear recommendation by the veterinary team. Guidelines can help veterinarians to minimize this obstacle, strengthen the human-pet-veterinary bond, and improve the quality of life of cats.
Goals:
The goals of this article are to assist veterinarians to: Deliver consistent high-quality care to senior cats. Promote longevity and improve the quality of life of senior cats by: recognizing and controlling health risk factors; facilitating and promoting early detection of disease; improving or maintaining residual organ function; and delaying the progression of common conditions. Define aspects of screening, diagnosis, treatment and anesthesia of senior cats.
The aim of this study was to describe the prevalence and severity of behavioural changes associated with age and their relationship to risk factors such as sex, reproductive status, bodyweight and age.
A cross-sectional study design was chosen. A total of 325 geriatric dogs were included. Owners of dogs older than nine years were interviewed by a veterinary behaviourist. Structured phone interviews were used to gather information about four behavioural categories related to cognitive impairment: sleep/wake cycles, social interaction, learning and house training and signs of disorientation.
Signs of cognitive impairment showed a prevalence of 22.5 per cent in geriatric dogs. Sex and age emerged as significant predictor variables. Females and neutered dogs were significantly more affected than males and entire dogs, respectively. Prevalence and severity increased with age. Although weight was not a statistically significant predictor variable, smaller animals had greater odds of showing age-related cognitive impairment. The most impaired behavioural categories were social interaction and house training.
Age-related behavioural changes should be considered by practicing veterinarians because of their relative high prevalence among geriatric dogs, especially in females.
This study was designed to evaluate the efficacy of a citronella bark collar and a new, scentless spray bark collar in a veterinary hospital or a similar kennel-type environment. Forty-one dogs were included in the study. The efficacy of each collar was evaluated independently in comparison to control as well as in a crossover design. Thirty of the dogs were evaluated with the citronella collar, with 76.7% showing a reduction in barking. Twenty-nine dogs were evaluated with the scentless collar, with 58.6% showing a reduction in barking. The improvement over the control collars was statistically significant with both the citronella and scentless collars.
The effects of long-term treatment with both antioxidants and a program of behavioral enrichment were studied as part of a longitudinal investigation of cognitive aging in beagle dogs. Baseline performance on a battery of cognitive tests was used to assign 48 aged dogs (9-12 years) into four cognitively equivalent groups, of 12 animals per group: Group CC (control food-control environment), group CE (control food-enriched environment); Group AC (antioxidant fortified food-control environment); Group AE (fortified food-enriched environment). We also tested a group of young dogs fed the control food and a second group fed the fortified food. Both groups of young dogs received a program of behavioral enrichment. To evaluate the effects of the interventions on cognition after 1 year, the dogs were tested on a size discrimination learning task and subsequently on a size discrimination reversal learning task. Both tasks showed age-sensitivity, with old dogs performing more poorly than young dogs. Both tasks were also improved by both the fortified food and the behavioral enrichment. However, in both instances the treatment effects largely reflected improved performance in the combined treatment group. These results suggest that the effectiveness of antioxidants in attenuating age-dependent cognitive decline is dependent on behavioral and environmental experience.
The current study describes both Abeta and tau abnormalities that accumulate in the brains of aged (16-21 years), but not young (<4 years) clinically characterized cats. Diffuse plaques that were morphologically different from what is typically observed in the human brain could be detected with 4G8 (Abeta17-24) or an Abeta1-42-specific antibody but not with N-terminal Abeta or an Abeta1-40-specific antibody. SELDI-TOF mass spectrometry experiments indicated that cat brain Abeta consisted almost entirely of Abeta1-42. Markers of tau hyperphosphorylation (AT8 and PHF-1) labeled a subset of neurons in two aged animals. In the hilus of the hippocampus, a subset of AT8 positive neurons showed a sprouting morphology similar to that observed in human brain. Western blot analysis with antibodies against hyperphosphorylated tau indicated that tau is hyperphosphorylated in the aged cat and contains many of the same epitopes found in Alzheimer's disease (AD) brain. Thus, the aged cat brain develops AD-related lesions with important morphological and biochemical differences compared to human brain.
Aging pets often suffer a decline in cognitive function (eg, memory,learning, perception, awareness) likely associated with age-dependent brain alterations. Clinically, cognitive dysfunction may result in various behavioral signs, including disorientation; forgetting of previously learned behaviors, such as house training; alterations in the manner in which the pet interacts with people or other pets;onset of new fears and anxiety; decreased recognition of people, places, or pets; and other signs of deteriorating memory and learning ability. Many medical problems, including other forms of brain pathologic conditions, can contribute to these signs. The practitioner must first determine the cause of the behavioral signs and then determine an appropriate course of treatment, bearing in mind the constraints of the aging process. A diagnosis of cognitive dysfunction syndrome is made once other medical and behavioral causes are ruled out.
Visuospatial learning and memory impairments are an early marker for age-related cognitive decline and Alzheimer's disease. Similar to humans, aged dogs show visuospatial learning and memory deficits (). One hundred and nine beagle dogs ranging between 0.25 and 11.99 years were tested on a visuospatial delayed non-matching to position (DNMP) task to better characterize the progression of visuospatial deficits in the dog. Age predicted 48.2% of the variability in learning the DNMP, with dogs ranging from 1 to 11.99 years generally making more errors with increasing age. By contrast, puppies (<1 year) likely were showing developmental deficits, possibly due to an immature prefrontal cortex. Mild visuospatial deficits were detected by 6 years, which precedes the typical onset of amyloid-beta (Abeta) accumulation in the dog brain by two years, and can serve as an early marker for cognitive decline in the dog. These findings suggest that (1) age-related changes in visuospatial function in the dog models that seen in humans, further validating the dog as a model for human aging and dementia; and (2) other mechanisms, such as oxidative stress, soluble Abeta oligomers or cholinergic deficits, are likely contributing to the early impairment.
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.
With improvements in nutrition and veterinary medicine the life expectancy of pet cats is increasing. Accompanying this growing geriatric population there are increasing numbers of cats with signs of apparent senility. A recent study suggests that 28 per cent of pet cats aged 11 to 14 years develop at least one geriatric onset behavioural problem, and this increases to over 50 per cent for cats of 15 years of age or older. While behavioural changes may result from systemic illness, organic brain disease or true behavioural problems, the possibility of age-related cognitive dysfunction is often overlooked. Studies have revealed a number of changes in the brains of geriatric cats that showed signs of cognitive dysfunction, and potential causes include vascular insufficiency leading to hypoxia, increased free radical damage and the deposition of beta-amyloid plaques and/or the modification of other proteins. By recognising the importance of behavioural changes in old cats, investigating them fully for potentially treatable medical conditions, and instigating dietary and environmental modifications to meet their changing needs, we can make the lives of our geriatric cats much more comfortable and rewarding.
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.