Monday, 16 December 2013

The Effects of Hormone Catecholamines - Dopamine(3)

Catecholamines, derived from the amino acid tyrosine, produced by the adrenal glands, which are found on top of the kidneys. are epinephrine (adrenaline), norepinephrine (noradrenaline) and dopamine. The hormone are released into the blood during times of physical or emotional stress.
17. Dopamine and learning
Individuals make choices and prioritize goals using complex processes that assign value to rewards and associated stimuli. According to the University of Michigan in rat study, dopamine acts selectively in a form of stimulus-reward learning in which incentive salience is assigned to reward cues. In individuals with a propensity for this form of learning, reward cues come to powerfully motivate and control behaviour. This work provides insight into the neurobiology of a form of stimulus-reward learning that confers increased susceptibility to disorders of impulse control(17).

18. Dopamine on cellular and humoral immune responses
In vitro and in vivo studies have demonstrated that apart from its hemodynamic action dopamine can modulate immune responses. According to the study by Institut für Anästhesiologie und Operative Intensivmedizin, Universitätsklinikum, dopamine reduces the synthesis of proinflammatory and induces the synthesis of anti-inflammatory mediators. Dopamine inhibits neurohormone synthesis, lymphocyte proliferation and platelet aggregation. It reduces the phagocytic activity of neutrophils and induces apoptosis. Particularly with regard to sepsis, where high serum dopamine levels are reached by enhanced endogenous production, exogenous application and impaired clearance, this immunomodulation may have a clinical impact(18).

19. Dopamine and Salience
What roles do mesolimbic and neostriatal dopamine systems play in reward? Do they mediate the hedonic impact of rewarding stimuli? Do they mediate hedonic reward learning and associative prediction? According to the study by University of Michigan,  instead that dopamine may be more important to incentive salience attributions to the neural representations of reward-related stimuli. Incentive salience, we suggest, is a distinct component of motivation and reward. In other words, dopamine systems are necessary for 'wanting' incentives, but not for 'liking' them or for learning new 'likes' and 'dislikes'(19).

20. Dopamine and human idea generation and creative drive
According to the study of FRONTOTEMPORAL AND DOPAMINERGIC CONTROL OF IDEA GENERATION AND CREATIVE DRIVE by Alice W. Flaherty , mesolimbic dopamine influences novelty seeking and creative drive. Dopamine agonists and antagonists have opposite effects on goal-directed behavior and hallucinations. Creative drive is not identical to skill—the latter depends more on neocortical association areas. However, drive correlates better with successful creative output than skill does(20).

21. Dopamine and  natriuresis (sodium loss) in the kidneys
Diuretic and natriuretic effects of renal dopamine (DA) are well established. In the study of male Wistar rats to determine the pattern of UDAV during volume expansion and to characterize the involvement of monoamine-oxidase (MAO) and aromatic amino-acid decarboxylase (AADC) , found that in C rats UDAV (ng/30 min/100g BWt) increased in the first 30 min expansion from 11.5 +/- 1.20 to 21.8 +/- 3.10 (p < 0.05) and decreased thereafter. IMAO showed a similar pattern but significantly higher than C at 30 min expansion (32.5 +/- 2.20, p < 0.05). IMAO greatly reduced MAO activity from 8.29 +/- 0.35 to 1.1 +/- 0.03 nmol/mg tissue/hour and significantly increased diuresis and natriuresis over controls. BNZ abolished the early UDAV peak to 3.2+/-0.72 (p < 0.01) and though, UDAV increased over C after 60 min expansion, natriuresis and diuresis were diminished by BNZ treatment. Results indicate that an increment in renal DA release into urine occurs early in expansion and in a peak-shaped way.(21).

22. Dopamine and obesity
According to the study by Institute for Translational Medicine and Therapeutics, University of Pennsylvania, chronic intake of high-fat (HF) diet is known to alter brain neurotransmitter systems that participate in the central regulation of food intake. Dopamine (DA) system changes in response to HF diet have been observed in the hypothalamus, important in the homeostatic control of food intake, as well as within the central reward circuitry [ventral tegmental area (VTA), nucleus accumbens (NAc), and pre-frontal cortex (PFC)], critical for coding the rewarding properties of palatable food and important in hedonically driven feeding behavior(22).

23. Dopamine and noradrenaline on cardiovascular function
In the study to assess the short-term haemodynamic effects of terminating dopamine and/or a combination of noradrenaline and nitroglycerin infusions in 21 patients in acute respiratory failure, found that off treatment, stroke index and cardiac index decreased significantly from 40.2 to 36.9 ml m-2 (P < 0.02) and from 3.80 to 3.42 litres m-2 (P < 0.02), respectively. Cardiac filling pressures decreased significantly and systemic vascular resistance increased, when infusions were stopped. As to heart rate, mean arterial pressure, mean pulmonary arterial pressure, right and left ventricular ejection fraction there were no significant changes between the data obtained during and off treatment. Although the haemodynamic status was significantly better during treatment with dopamine and/or noradrenaline-nitroglycerin in some respects, the overall beneficial effects of inotropic support were much less than anticipated(23).

24. Dopamine and Immunoregulatory
The neurotransmitter dopamine (DA) is an important molecule bridging the nervous and immune systems. According to the study by the Ohio State University, Columbus, DA through autocrine/paracrine manner modulates the functions of immune effector cells by acting through its receptors present in these cells. DA also has unique and opposite effects on T cell functions. Although DA activates naïve or resting T cells, but it inhibits activated T cells. In addition, changes in the expression of DA receptors and their signaling pathways especially in T cells are associated with altered immune functions in disorders like schizophrenia and Parkinson's disease. These results suggest an immunoregulatory role of DA(24).

25. Dopamine toxicity
Parkinson's disease (PD) is a common age-related neurodegenerative disorder. Dopamine neurotoxicity, mediated through oxidative stress, is implicated in disease pathogenesis. According to the study of using 6-hydroxydopamine hemiparkinsonian mouse model and transgenic DJ-1 knockout mice by the Felsenstein Medical Research Centre, Tel Aviv University, our experimental data point to a novel potential protective function of DJ-1, which could be used as a therapeutic tool(25).

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