Dopaminergic System in the Aged Brain: Evidence for a Selective Loss of D-1 But Not D-2 Receptors

Abstract

Although aging of the brain is often associated with disease, it has been demonstrated that more than 70% of old people lives until death without evident signs of cerebral pathology. The so-called well preserved aged show a slight impairment of many psychological and neurological functions. Over the past ten years, a few significant concepts rose from studies on neurotransmitters and receptors in the aged brain: the plasticity of neurons and synapses, a neuronal hierarchy, a differential vulnerability and the so-called threshold phenomena (Bergener et al., 1985; Walker et al., 1983). Studies on plasticity of neurons and synaptogenesis are one of the most encouraging field for understanding normal and pathological aging and for generating drugs which can help to avert and to treat diseases. An increased dendritic synaptogenesis has been reported in neocortex following complex environment exposure both in adult and old rats (Greenough W., 1984). Although this event may diminish in senescent animals, the data suggest that the capacity for experience-dependent synaptogenesis is maintained through a significant proportion of the life-span. This is of particular interest for learning and memory. In fact, such a synaptic efficiency may well be a nuerophysiological mechanism for storage of information in the central nervous system.