Aging and Cognitive Dysfunction in Dogs and Cats
Dogs and cats, just like humans, start to slow down a little, both physically and mentally, as they get older. We may notice our senior pets beginning to show less interest in playing, less enthusiasm about going on walks, or even in interacting with us. Many pet owners believe that these changes are unavoidable aspects of aging. While some of these behaviors, and certainly a reduction in physical ability, are a normal part of the aging process, some changes may be signs of cognitive dysfunction or other treatable medical conditions.
Cognitive dysfunction syndrome (CDS) is a degenerative disease in dogs and cats that is similar to Alzheimer’s disease in humans. CDS differs from normal brain aging. As animals age, the mitochondria in their cells become less efficient, producing less energy and more damaging free radicals which increases oxidative stress throughout the body. The brain is particularly susceptible to damage from freed radicals due to its high concentration of lipids, high oxygen demand, and limited natural antioxidant enzymes. While a certain amount of oxidative damage and neuronal loss is a normal aspect of aging, excessive oxidative stress may result in accumulations of toxic proteins called beta amyloid and phosphorylated tau protein in the brain. This leads to death of the cells and the signs of CDS. Protein accumulation and neuron loss is most notable in the hippocampus and frontal cortex of the brain. These areas are integral in memory formation and learning. While normal brain aging may result in lowered activity level, decreased responsiveness, and slightly lessened interest in social behavior, CDS will manifest itself in more severe symptoms of disorientation, forgetfulness, changes in sleep-wake cycles, and increased anxiety.
Cognitive dysfunction syndrome presents itself through various behavioral changes that are summed up in the acronym DISHA: Disorientation, Interaction, Sleep-wake cycle, House training, and Activity. Animals suffering from CDS will often display decreased interest in social interaction and may suddenly start soiling the house despite having been well housetrained before. Additionally, some animals sleep more during the day, but then wake in the middle of the night vocalizing anxiously or pacing. Signs of disorientation and forgetfulness can include sticking their nose toward the hinge side of the door when waiting to be let out or failure to respond to previously trained cues even when the pet is able to clearly see or hear them. Owners should make note of any signs like these, no matter how small the problem may seem, and report them to their veterinarian promptly. (The earlier treatment is initiated, the more favorable the response can be.)
Cognitive dysfunction syndrome is diagnosed by first eliminating other medical conditions that may be causing the symptoms. (The only truly definitive way to diagnose CDS is by brain biopsy via autopsy.) Though there is no cure for CDS, there are multiple treatment modalities that can be used to temporarily reverse decline, greatly improve symptoms, and slow the ultimate progression of the disease. Your veterinarian may suggest a combination of supplements, dietary changes, drug therapy, and/or training/enrichment interventions to ameliorate symptoms.
Preventative measures can also be implemented for healthy animals, as brain changes associated with cognitive decline and CDS can begin to show as early as seven years of age in dogs and ten years in cats.
Multiple dietary supplements have been shown to improve symptoms of cognitive decline and CDS. Oral S-adenosylmethionine, or SAM-e, (marketed as Novifit® or Denosyl®) is reported to decrease oxidative stress and aid neuron transmission. It can help animals regain previously learned behaviors and may correct sleep/wake cycles and elimination problems. Apoaequorin (Neutricks®) is a calcium-binding protein derived from jellyfish with neuroprotective effects. Studies have shown it to improve attention and learning in older dogs. Senilife® is a supplement containing a mixture of antioxidants as well as phosphotidylserine, a phospholipid that increases fluidity of cell membranes and has been shown to reduce cognitive deficits in both humans and animals. Aktivait® also contains phosphotidylserine and antioxidants, as well as omega-3 fatty acids, vitamin E, and other compounds that support brain function and metabolism, though this is not currently licensed for use in the United States.
There are multiple diets that have been specially formulated to improve or prevent symptoms of cognitive decline in older dogs. Hill’s® Prescription Diet® b/d® contains a wide range of antioxidants, omega-3 fatty acids, and other beneficial ingredients. It has been shown to improve memory, learning, and clinical signs of CDS. Purina One® Smartblend® Vibrant Maturity® 7+ formula contains medium-chain triglycerides, which are broken brown into ketones in the body, providing an alternative energy source to the brain. One study showed a significant improvement on multiple cognitive tasks in dogs fed this diet versus placebo. Purina® Pro Plan® Bright Mind® also contains medium chain triglycerides. Ask your vet about the best combination of supplements and diet for your individual pet, as some of them are prescription only. Many veterinarians suggest that you start a diet or supplement as a preventative measure in all dogs seven years and older.
If your pet is already showing clinical signs of cognitive dysfunction syndrome, your veterinarian may suggest medication in addition to dietary changes. Selegiline (brand name Anipryl®) is a monoamine oxidase B inhibitor, which increases dopamine transmission. It also decreases free radicals and has neuroprotective effects. Selegiline can also be used off-label to treat cats. Currently, this is the only drug licensed to treat CDS in North America. However, some countries outside North America allow the use of propentofylline (Vivitonin or Karsivan), a drug that inhibits platelet aggregation and improves blood flow in order to treat lethargy and dullness in older dogs. Some countries also allow the use of Nicergoline, a medication containing adrenergic antagonists that also increases blood flow in the brain and enhances neuronal transmission.
Training and Enrichment
Just like the muscles in our bodies, our brains require regular ‘exercise’ to stay sharp; therefore, both people and their pets must, in a sense, ‘use it or lose it’. When a senior pet starts to slow down, many owners make the mistake of almost completely halting the enriching activities that were previously part of the pet’s daily routine. We call this “the shrinking world syndrome.” Maybe you decide that because of your dog’s developing arthritis, you’ll skip walks or stop them altogether, all the while telling yourself, “she prefers lying around all day now that she’s older.” Maybe your cat, which previously followed you around the house constantly soliciting attention, now spends most of the day sleeping in the corner, but you make no effort to engage with her for fear of disturbing her. (Excessive resting/sleeping in cats is actually a sign of poor welfare as cats should naturally be relatively active at times.) As our pets age, we often stop initiating or encouraging play or exercise, believing they are happy lying around the house just snoozing. We also stop teaching older pets new things. Learning is important for maintaining cognitive health and flexibility. These changes significantly decrease the variability in our pets’ daily lives that provides crucial enrichment and stimulation and is detrimental to our pets’ cognitive health.
Even if your pet has developed some physical limitations, such as arthritis or other conditions causing chronic pain, you can take her to a nearby park just to sniff around on a loose leash at all the novel smells, or teach her new tricks that are appropriate for her physical ability, such as nose touch, shake, or bow. Give a portion of her meals in a puzzle toy or create doggie popsicles out of frozen chicken broth or canned pumpkin for another low-exertion enrichment activity. Food dispensing toys are also a great enrichment option for cats with limited mobility. You can also offer your cat visual enrichment by giving her an accessible resting place with a view of the bird feeder in the backyard or a fish tank on the kitchen counter. You can encourage social interaction by clicker training your cat to learn simple behaviors like “target.” There is strong evidence that continuous stimulation helps maintain cognitive function and delays decline in healthy animals. Incorporating daily enrichment before the onset of clinical signs can greatly reduce your senior pet’s risk of negative behavioral changes and is fairly easy to implement with a few small alterations to your routine. And in the end, it’s worth it. These small changes can add years of youthfulness to your pet’s life.
Glossary of Terms
Mitochondria: The organelle responsible for energy production
Free Radicals: Especially reactive atoms that can cause damage to cells and their DNA. Can be produced internally by metabolic processes (i.e. energy production) or by external sources such a tobacco or toxins
Oxidative Stress: Damage to cells caused by free radicals inadequately neutralized by antioxidants
Reactive Oxygen Species: Free radicals
Antioxidant enzymes: Proteins that neutralize free radicals in order to prevent cellular damage
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Authored by Mariah Dingus and Lore I. Haug, DVM, MS, DACVB