Figure: 1 NEURONAL BIOCHEMICAL PROCESSES INVOLVING DOPAMINE presynaptic neuron

Dopamine containing neurons arise mainly from DA cell bodies in the substantia nigra and ventral tegmental area in mid-brain region (Tarazi, et aI., 2001; 1996; Creese, et. aI., 1997; Royh, et. aI., 1991; Carlsson, 1993; Lookingland, et aI., 1995). Dopaminergic system is organized into four major subsystems (i) the nigrostriatal system involving neurons projecting from the substantia nigra pars compacta to the caudateputamen of the basal ganglia. This is the major DA system in the brain as it accounts for about 70% of the total DA in the brain, and its degeneration makes a major contribution to the pathophysiology of Parkinson's disease; (ii) the mesolimbic system that originates in the midbrain tegmentum and projects to the nucleus accumbens septi and lateral septal nuclei of the basal forebrain as well as the amygdala, hippocampus, and the entorhinal cortex, all of which are considered components of the limbic system and so are of particular interest for the patho-physiology of idiopathic psychiatric disorders; (iii) the mesocortical system, which also arises from neuronal cell bodies in the tegmentum which project their axons to the cerebral cortex, particularly the medial prefrontal regions; (iv) the tuberinfimdibular pathway, which is a neuroendocrinological pathway arising from the arcuate and other nucl~i of the hypothalamus and ending in the median eminence of the inferior hypothalamus. DA released in this system exerts regulatory effects in the anterior pituitary and inhibits the release of prolactin. DA is involved in the control of both motor and emotional behavior. Despite the large number of crucial functions it performs, this chemical messenger is found in a relatively small number of brain cells. In