Dopamine central functions

Learning, memory, sensory faculties (e.g., smell, vision or hearing) or emotions are mediated by neurons which communicate via GABA, glutamate and serotonin as the major neurotransmitters in addition to acetylcholine, adrenaline, noradrenaline and dopamine which also exhibit central functions (see above] [90]. 

L-Tyrosine metabohsm and catecholamine biosynthesis occur largely in the brain, central nervous tissue, and endocrine system, which have large pools of L-ascorbic acid (128). Catecholamine, a neurotransmitter, is the precursor in the formation of dopamine, which is converted to noradrenaline and adrenaline. The precise role of ascorbic acid has not been completely understood. Ascorbic acid has important biochemical functions with various hydroxylase enzymes in steroid, dmg, andhpid metabohsm. The cytochrome P-450 oxidase catalyzes the conversion of cholesterol to bUe acids and the detoxification process of aromatic dmgs and other xenobiotics, eg, carcinogens, poUutants, and pesticides, in the body (129). The effects of L-ascorbic acid on histamine metabohsm related to scurvy and anaphylactic shock have been investigated (130). Another ceUular reaction involving ascorbic acid is the conversion of folate to tetrahydrofolate. Ascorbic acid has many biochemical functions which affect the immune system of the body (131). 

Important products derived from amino acids include heme, purines, pyrimidines, hormones, neurotransmitters, and biologically active peptides. In addition, many proteins contain amino acids that have been modified for a specific function such as binding calcium or as intermediates that serve to stabilize proteins—generally structural proteins—by subsequent covalent cross-hnk-ing. The amino acid residues in those proteins serve as precursors for these modified residues. Small peptides or peptide-like molecules not synthesized on ribosomes fulfill specific functions in cells. Histamine plays a central role in many allergic reactions. Neurotransmitters derived from amino acids include y-aminobutyrate, 5-hydroxytryptamine (serotonin), dopamine, norepinephrine, and epinephrine. Many drugs used to treat neurologic and psychiatric conditions affect the metabolism of these neurotransmitters. 

Benkirane, S. Arbilla, S. and hanger, S.Z. A functional response to D1 dopamine receptor stimulation in the central nervous system Inhibition of the release of [ H]-serotonin from the rat substantia nigra. Naunyn-Schmiedebergs Arch Pharmacol 335 502-507, 1987. 

If these changes are also present in central dopaminergic reward pathways, it may be that the allele is linked to impaired perception of reward. It has been suggested that an inherited dopamine deficit could be overcome by nicotine, which stimulates dopamine release thereby restoring dopamine function to normal levels [17]. In this way the polymorphism could confer susceptibility to tobacco use. 

The answers are 321-cT 322-e, 323-i. (Hardman, pp 238-239, 791.) Reserpine is an adrenergic neuronal blocking agent that causes depletion of central and peripheral stores of NE and dopamine Reserpine acts by irreversibly inhibiting the magnesium-dependent ATP transport process that functions as a carrier for biogenic amines from the cytoplasm... 

Dopamine is an intermediate product in the biosynthesis of noradrenaline. Furthermore it is an active transmitter by itself in basal ganglia (caudate nucleus), the nucleus accumbens, the olfactory tubercle, the central nucleus of the amygdala, the median eminence and some areas in the frontal cortex. It is functionally important, for example in the extra-pyramidal system and the central regulation of emesis. In the periphery specific dopamine receptors (Di-receptors) can be found in the upper gastrointestinal tract, in which a reduction of motility is mediated, and on vascular smooth muscle cells of splanchnic and renal arteries. Beside its effect on specific D-receptors, dopamine activates, at higher concentrations, a- and -adrenoceptors as well. Since its clinical profile is different from adrenaline and noradrenaline there are particular indications for dopamine, like situations of circulatory shock with a reduced kidney perfusion. Dopamine can dose-dependently induce nausea, vomiting, tachyarrhythmia and peripheral vasoconstriction. Dopamine can worsen cardiac ischaemia. 

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