3.3FUNCTIONAL CHANGES 3.3 FUNCTIONAL CHANGES

There are many functional changes that can occur with advancing age:



Central nervous system

Impaired neurotransmission results from the decreased production of neurotransmitters and reduced breakdown of those that are produced.

Reduced serotonin levels increase sleeping time and may cause neudisorders and depression. Depletion of noradrenaline in the brain is also associated with depression.

Hypoxia leads to short-term memory loss, but not a loss of long-term memory. Oxygen supplementation can reverse this memory loss.

Signs of senility are frequently recognised in older animals and are probably associated with ageing changes in the nervous system but the precise cause-effect relationships have been poorly documented (see Table 3.3).

Regular exercise improves many bodily functions probably through its effects on the neuroendocrine system by increasing the secretion of growth hormone and reducing the secretion of adrenocorticotrophic hormone (ACTH) and glucocorticoids.


Peripheral nervous system

With advancing age reduced function may occur in both the sympathetic and parasympathetic parts of the peripheral nervous system. Changes may be presynaptic, synaptic or postsynaptic resulting in impaired transmission of impulses to and from the CNS. This may produce abnormal neurological and neuromuscular function leading to sluggish reflexes, reduced pain response, impaired proprioception and difficulty with locomotion. The animal may be less able to respond to sudden stresses placed on it because of impaired ability to maintain homeostasis through neuroendocrine control mechanisms.

Inexperienced clinicians may find it difficult to differentiate between proprioceptive deficits and muscular weakness in older animals.



Treatment

Recently two drugs - propentofylline (VMtonin, Hoechst) and nicergoline (Fitergol, Rhone Meneux) - have been granted veterinary product licences based upon their ability to improve the signs associated with ageing in dogs such as lethargy and dullness. They both have numerous pharmaactions on the bod~ but their main mechanism of action is thought to be an increase in b~od supply to the brain resulting in improved neufunctions.



Propentofylline

Is indicated for the treatment of lethargy and dullness in old dogs.


Dose

12.5-100 mg b.i.d. depending upon body weight.



Nicergoline

Is an µ-adrenoreceptor antagonist and is indicated in the treatment of age-related lethargy and dullness in dogs.


Dose

0.25-0.5 mg/kg daily.