Sunday, 15 December 2013

The Effects of Hormone Catecholamines - Dopamine (1)

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.
1. Acetylcholine-dopamine and CNS disorders
The substantia nigra pars compacta and ventral tegmental area of midbrain dopaminergic nuclei and their respective forebrain and cortical target areas are well established as serving a critical role in mediating voluntary motor control, as evidenced in Parkinson's disease, and incentive-motivated behaviors and cognitive functions, as exhibited in drug addiction and schizophrenia, respectively. According to the study by The University of Memphis, acetylcholine may be as important in regulating dopaminergic transmission. Midbrain dopaminergic cell tonic and phasic activity is closely dependent upon projections from hindbrain pedunculopontine and the laterodorsal tegmental nuclei, which comprises the only known cholinergic inputs to these neurons(1). Other study indicated that combinatorial signaling through dopamine and serotonin (DA and 5-HT) receptors can regulate the brain region- and cell-type specific pMeCP2 in the CNS(1a).

2. The effects of Dopamine and dobutamine on heart rate
In the study of twenty patients with symptomatic CHF (systolic dysfunction) were enrolled. After recording one-hour baseline electrocardiographs (ECGs), patients were randomly selected for either dopamine (4 micrograms/kg/minute, Group A) or dobutamine (4 micrograms/kg/minute, Group B) treatment for three days, conducted by Taichung Veterans General Hospital, found that Dopamine and dobutamine have comparable therapeutic effects in patients with CHF, but low-dose dopamine more favorably affects cardiac autonomic function(2).

3. Dopamine and blood pressure and cerebral hemodynamics
In a Standard meta-analytic techniques, including random and fixed effects models used to calculate combined effect size correlations and significance levels showed that Dopamine administration increases mean and systolic blood pressure in hypotensive preterm infants, and is more effective than dobutamine, colloid or hydrocortisone alone. Dopamine administration is associated with increased CBF, with greater increases in CBF in hypotensive than in normotensive preterm infants. Dopamine is not associated with a greater incidence of adverse effects than other therapies used to treat hypotension(3).

4. Dopamine in schizophrenia and Parkinson's disease
The neurotransmitter dopamine (DA) and the dopaminergic neurones play an important role in schizophrenia and Parkinson's disease (PD). According to the study byUniversity of Southampton, Royal South Hants Hospital, A decrease in DA in the substantia nigra of the brain has been implicated as the cause of PD. By contrast, it is argued that a functional excess of DA or oversensitivity of certain DA receptors is one of the causal factors in schizophrenia(4).

5. Dopamine and Attention deficit hyperactivity disorder
Through neuromodulatory influences over fronto-striato-cerebellar circuits, dopamine and noradrenaline play important roles in high-level executive functions often reported to be impaired in attention-deficit/hyperactivity disorder (ADHD). According to the study by University of Cambridge, Cambridge, United Kingdom, Medications used in the treatment of ADHD (including methylphenidate, dextroamphetamine and atomoxetine) act to increase brain catecholamine levels. However, the precise prefrontal cortical and subcortical mechanisms by which these agents exert their therapeutic effects remain to be fully specified(5).

6.  Dopamine  and restless legs syndrome
Restless legs syndrome (RLS) is a common neurological disorder causing considerable impairment to daily living. In a study to assess the reporting quality of published RCTs according to the Consolidated Standards of Reporting Trials (CONSORT) statement and to synthesize the study results in terms of efficacy and tolerability to inform the clinical management of RLS, showed that
DAs were significantly more efficacious in the treatment of RLS compared with placebo(6).

7. Dopamine  receptors and cognitive and motor function
According to the study by, Columbia University College of Physicians & Surgeons, repeated administration of this methamphetamine (5 mg/kg administered three times at 2-h intervals) leads to a transition from horizontal hyperlocomotion to excessive orofacial stereotypy (taffy pulling) only in wild type and D3 mutants. In both genotypes, this transition is accompanied by a change in the relative ratios of striatal neuronal activation in two neurochemically distinct compartments, with striosomal neuronal activation exceeding that of the striatal matrix during stereotypy. Both the stereotypic response to METH and the associated predominant activation of neurons located in striosomes require D2-receptor expression. These studies indicate a differential requirement for D1- and D2-like receptor activation in mediating the effects of METH on cognitive and motor function(7). Other indicated that the 'D3 Dopamine Receptor Hypothesis' suggests D3 antagonists could prevent sensitization, and may interrupt the development of psychosis when administered during the prodromal phase of psychotic illness(7a).

8.  Dopaminergic neurotransmission and behavioral changes
Dehydration is a powerful stimulus causing disequilibrium in homeostasis of water and electrolytes resulting from depletion in total body water. In the study of desert animals allows improved understanding about water balance and resistance to dehydration and associated behavioral changes, including those related to voluntary movements, showed that dehydration is able to increase dopaminergic neurotransmission, which might be involved in generating hyperactivity in this desert animal(8).
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