Neuropharmacology of depression in aging and age-related diseases

Depression in the elderly is nowadays a predominant health care problem, mainly due to the progressive aging of the population. It results from psychosocial stress, polypathology, as well as some biochemical changes which occur in the aged brain and can lead to cognitive impairments, increased symptoms from medical illness, higher utilization of health care services and increased rates of suicide and non-suicide mortality. Depression may be also caused by a various number of drugs currently administered; this is remarkable especially in elderly people, where polypathology is often associated with polypharmacotherapy. However, the pathogenesis of geriatric depression is not well understood; major depression may arise from dysfunction of the limbic-hypothalamic-pituitary-adrenal axis. Some clinical observations also suggest that striato-frontal dysfunction is associated with late life depression. A number of hypotheses have been made, focusing that mood disturbances are probably linked to a disturbed central metabolism of monoamines 5-hydroxytryptamine, noradrenaline and dopamine; however most of this knowledge is derived from animal models. Parkinson's and Alzheimer's diseases are age-related diseases associated to decreased activity or brain lesions in the orbital frontal cortex and basal ganglia. These observations lead to the hypothesis that the dysfunction of one or more of the cortical basal ganglia-thalamic neuronal loops are involved in the pathophysiology of primary and secondary depression. This dysfunction may be mediated by decreased serotonin release and probably, also by reduction in serotonin receptors. Development of novel approaches such as dynamic brain imaging methods, together with indirect knowledge coming from the effects of new antidepressants, will increase the understanding of neurochemistry of depression in old age.