Brain aging in dogs: Prevention and treatment: Second of a two-part series

Last month, we investigated the contributions and causes of cognitive dysfunction (CD) in dogs as they age. One factor we looked at was oxidative damage, which can cause inflammation or damage to the neurons. Increased oxidative stress appears to affect all major classes of molecules involved in neurotransmission. Development of oxidative stress may not be independent of energy source or use, and molecular effects may not be independent of energy intake and use. For example, intermittent fasting has been reported to induce the production of brain-derived neurotrophic factor (BDNF) — a key neurotrophic factor associated with neurogenesis and molecular learning and memory, particularly in the hippocampus.

Although we are truly in our infancy in terms of understanding these complex inter-relationships, the future looks brighter. Since obesity is an epidemic in pets, we are unlikely to encourage our clients to engage in intermittent fasting for their pets. Despite this, there are dietary strategies available for addressing oxidative stress. Other forms of intervention for preventing or treating cognitive decline include supplements, medications, and cognitive and physical stimulation.

Foods

New foods are being developed all the time, but two should catch our attention. Prescription Diet b/d Canine (Hill's Pet Nutrition) is formulated to redress oxidative stress. It does so by providing high levels of antioxidants, including vitamins C and E and L-carnitine, to facilitate energy availability and enhance neuronal signal transmission. The diet combined with environmental stimulation demonstrated the strongest effect in laboratory dogs. Effects of such an antioxidant diet are also apparent in levels of BDNF, which have been shown to be similar to those found in young dogs.

Purina Veterinary Diets EN Canine Formula (Nestlé Purina) is designed to use medium-chain triglycerides (MCTs) as an energy source and is accordingly high in omega-3 and omega-6 fatty acids, which may help maintain neuronal integrity. Both of these diets take advantage of antioxidants in the hopes of decreasing the effects of oxidative stress.

Supplements

Senilife (Ceva Santé Animale) uses antioxidants (resveratrol), structural enhancers of neuronal membranes (phosphatidylserine) and a coenzyme of neurotransmitter function (pyridoxine) to address the three factors that can affect brain aging. Aktivait (Vet Plus, U.K.; available only online in the United States) also addresses structural concerns by providing docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) and phosphatidylserine, plus the antioxidants vitamins C and E, selenium, N-acetyl cysteine and alpha-lipoic acid.

Medications

Selegiline (Anipryl — Pfizer) is a monoamine oxidase B inhibitor licensed to treat CD. It inhibits the degradation and recycling of the monoamine neurochemicals (i.e., norepinephrine, serotonin, dopamine), with its largest effect on dopamine. By providing increased neurochemical stimulation to neurons, their synapses are maintained, and the effects of BDNF are able to occur. This medication works best as a preventive and treatment if given when the first signs of CD begin. The most dramatic effect is noticed by clients if the dogs are moderately affected, but that's because the decline was so apparent. Treatment of CD with medication is another example of a situation in which treating early and often is preferred.

For some dogs that exhibit nonspecific signs of anxiety as their first behavioral changes with age, treatment with tricyclic antidepressants (TCAs) or selective serotonin reuptake inhibitors (SSRIs) may help. Clients typically notice diminished anxiety levels. Because these medications increase signal transduction efficiency, they help keep neurons plump and talking to each other. As a result, they may have protective and treatment roles for CD.

Cognitive and physical stimulation

New research is expanding our knowledge about the cognitive skills of dogs. The "smartest" dogs are likely the dogs that are intellectually stimulated.

Because dogs slow as they age, we should not assume that maturity and arthritis mean that dogs require less cognitive and physical stimulation. In fact, all the data — for dogs and for ourselves — suggest that we need more cognitive and physical stimulation with age. Aerobic exercise has been shown to slow cognitive change in human patients in the early stages of Alzheimer's disease, and mental exercise appears to have a physical benefit for such patients. If you think about what we know about brain energy use, this actually makes sense. The same association appears to be true for dogs. Using both cognitive and molecular measures, enhanced diets plus environmental enrichment (cognitive stimulation) have a greater effect on improving measures of problem solving in dogs than do either alone.

Physical exercise should be suited to the breed, behavioral pattern and health of the dog. Even arthritic dogs can benefit from walking and daily massage. Swimming will benefit all dogs. For those that dislike swimming or that do not have access to a place to swim, clients and veterinarians can consider underwater treadmills. These are fantastic for rehabilitation but are underappreciated as a regular (at least weekly) means of safe exercise and water massage for dogs that are severely arthritic. Failing all of this, severely arthritic dogs can benefit from undergoing range of frequent motion exercises in a bath tub filled with warm water — something devoted clients can do daily.

Dogs that liked to catch balls and Frisbees when young may not wish to jump, but they would be happy to chase or retrieve these same toys if they are rolled. Rolling food toys and puzzles also enhances and maintains eye-paw coordination, and since the toys and puzzles make noise, even dogs that are losing visual and auditory acuity can benefit.

Interestingly, cognitive stimulation for dogs may also include olfactory stimulation. We know from the human literature that all conditions involving cognitive impairment also involve decrements in olfactory ability. We know that biopsies of aged dogs' olfactory epithelia show depositions of amyloid among olfactory neurons. These patterns suggest that olfactory stimulation may be one form of cognitive stimulation to which older dogs can be exposed. Olfactory stimulation may be as simple as dragging a freshly cooked bone through grass and encouraging the dog to follow the path. The marrow from the bone can be the reward. This association between decrements in cognition and olfactory function may also suggest that we need to pay attention to the volatile olfactory component of our dogs' dinners. Warming food and providing warm broth allows odorant molecules to volatilize, stimulating a dog's brain and encouraging eating.

In addition to some scent work, other forms of cognitive stimulation may include basic obedience or clicker work, or working to teach new or maintain old tricks. Five minutes of such work three to four times a day can be priceless. Some of this can be incorporated into daily life. For example, if clients are getting up from the table, they can ask the dog to come with them, to sit or wait, and/or offer a paw. There is nothing better than ongoing stimulation and interaction.

Photo 1: Flash (right) was 12 years old when Toby (left, at 9 weeks) was adopted into the household. Raising this puppy became part of Flash's legacy, but the positive effects on his cognition, social and motor skills are clear in this photo.

Play with puppies (Photo 1) provides cognitive and physical stimulation for older dogs, enhances their aerobic scope and provides a foundation for good manners. Just be sure that the older dog likes other dogs and that the puppy cannot hurt the older dog.

Photo 2: Tess, 14 years old and in the buggy, was unable to go on the long walks the other dogs would take multiple times a week. Rather than leave her alone for hours at a time, her owners placed her in the buggy allowing her to experience novel and complex stimuli, use different muscles, have the company of the other dogs (here accompanied by Flash) and smell the world as she passed through it.

Social interaction and exposure to new stimuli is essential for keeping cognitive skills sharp. We often think that withdrawal from such social situations is normal for older dogs, when, instead, older dogs are just painful, unaware or unable to get where they can participate. Because they are slow and quiet, they are left behind. This is a huge mistake, and every effort should be made to include these older dogs. Pet strollers provide an underused option for older arthritic pets. As shown in Photos 2 and 3, strollers allow an old Australian shepherd to accompany her owners and the other dogs on the regular three-mile walks. While she is not getting aerobic exercise, she is using muscles involved in balance and attentiveness, while getting much needed social and olfactory stimulation. Also, she knows she is included and loved.

Photo 3: The positive effect on Tess of such stimulation is clear in her engaged and relaxed facial expression. Dogs of her age and debility are too often left alone, where they resort to sleep in the absence of cognitive stimulation.

Dr. Overall, faculty member at the University of Pennsylvania, has given hundreds of national and international presentations on behavioral medicine. She is a diplomate of the American College of Veterinary Behavior (ACVB) and is board certified by the Animal Behavior Society (ABS) as an Applied Animal Behaviorist.