Question

Explain in detail the physiological functions and mechanisms of action of a neurotransmitter (Dopamine) and explain how drugs can alter their function.

Answer 1

Physiological function of dopamine.

Dopamine is a neurotransmitter released by the brain that place a number of rules in human and other animals. Sum of its notable functions are are in.

Movement -

Part of brain called basal ganglia regulate movement. Basal ganglia intern depend on a certain amount of dopamine to function at peak efficiency. The action of dopamine occurs via dopamine receptor d1-5 dopamine reduces the influence of indirect pathway, and increases the action of the direct pathway within the basal ganglia. When there is a deficiency in dopamine in the brain, movement Mein become delayed uncoordinated. On the flip side if there is an excess of dopamine in the brain causes the body to make unnecessary movements such as repetitive tics.

Pleasure reward seeking behaviour-

Doberman is the chemical that mediate pleasure in the brain. It is released during pleasurable situations and stimulates one to seek out the pleasurable activity or occupation. This means food ,sex and several drugs of abuse or also stimulants of dopamine release in the brain, particularly in areas such as nucleus accumbens and prefrontal cortex.

Addiction-

Cocaine and amphetamine inhibit the uptake of dopamine. Cocain is dopamineTransporter blocker that competitively inhibit dopamine uptake to increase the presence of dopamine. Amphetamine increases the concentration of Dopamine in the synoptic grab but by a different mechanism. Amphetamine are similar in structure to dopamine and so can enter the presynaptic neurone via its dopamine Transporter. By entering amphetamine forces dopamine molecule out of their storage vesicle. The increasing presence of both these lead to increased pleasurable feeling and addiction.

Memory-

Levels of dopamine in the brain specially the prefrontal cortex helps in improved working memory. However this is delicate balance and as levels increase or decrease at normal levels memory Suffers.

Attention-

Dopamine helps in focus and attention. Vision helps a Dopamine response in the brain and this in turn helps to focus and direct attention. Dopamine may be responsible for determining what stays in The short-term memory based on an imagined response to certain information. Reduced dopamine concentration in the prefrontal cortex are thought to contribute to attention deficit disorder.

Cognition-

Dopamine in the prefrontal lobe of the brain controls the flow of information from other areas of the brain. Disorder of dopamine in this region lead to decline in neuro cognitive functions specially memory attention and problem solving. D1 receptors and D4 receptors are responsible for cognitive enhancing effect of dopamine. Some of the antipsychotic medications used in conditions like schizophrenia acts as dopamine antagonist. Older, so called "typical" antipsychotics most commonly act on D2 receptors while the earth topical drugs also act on D1 and D3 and D4 receptors

Prolactin secretion-

Dopamine is the main neuroendocrine inhibitor of secretion of prolactin from the anterior pituitary gland. Dopamine produced by neurones in the arcuate nucleus of the hypothalamus is released in the hypothalamo-hypophyseal blood vessel of the median eminence, which supply the pituitary gland. This acts on the lectotrope cells that producesuce prolactin. These cells can reduce prolactin in absence of dopamine. Vitamin is occasionally called prolactin inhibiting factor prolactin in hi beting hormone or prolacto statin.

Social functioning-

Low D2 receptor binding is found in people with social anxiety all social phobia. Some features of negative schizophrenia are thought to be related to low dopaminergic state in certain areas of the brain. On the other hand those with bipolar disorder in manic states become hyper social, as well as hypersexual. This is credited to an increase in dopamine. Mania can be reduced by dopamine blocking antipsychotic.

Psychosis-

Abnormally high dopaminergic transmission has been linked to psychosis and schizophrenia. Both typical and atypical antipsychotic work largely by inhibiting dopamine at the receptor level.

Pain processing-

Dopamine plays a role in pain processing in multiple levels of central nervous system. This includes the spinal cord, periaqueductal gray, thalamus, basal ganglia, insular cortex,and cingulate cortex. Low levels of dopamine are associated with painful symptoms that frequently occur in Parkinson's disease.

Nausea and vomiting -

Dopamine is one of the neurotransmitters implicated in the control of nausea and vomiting via interaction in the chemoreceptor trigger zone.

Mechanism mechanism of action

That dopaminemine is a natural cheticholamine formed by the decarboxylation of 3, 4 dihydroxy phenyl alanine. It is precursor of nor epinephrine and is also a neurotransmitter in certain areas of the central nervous system specially in the nigrostriatal tract, and in a few peripheral sympathetic nerves. The dopamine produces positive chronotropic and Inotropic effects on the myocardium resulting in increased heart rate and Cardiac contractility. This is accomplished directly by exerting and agonist action on beta adrenergic receptors and indirectly by causing release of norepinephrine from storage sites in sympathetic nerve ending.

Drugs drugs affecting dopamine action

Many many drugs effects the dopamine transmission directly by either blocking or stimulating its receptor. For example antipsychotic drug dopamine antagonist whereas bromocriptine used to treat hyperprolactinemia and Parkinson's disease is dopamine agonist.

Dopamine agonist.-

They are class of drugs that binds to activate dopamine receptors in the brain. They mimics the action of naturally occurring dopamine in the brain causing the neurones to react as they would to dopamine. They trick the brain into thinking it's getting the dopamine it needs. They are used to treat low dopamine conditions including Parkinson's disease and restless legs syndrome. Restless leg syndrome is a sleep disorder that causes an unpleasant tingling for twitching sensation in the legs when lying or sitting down, resulting in an irresistible urge to move them and in insomnia. Like Parkinson's disease it to seems to be caused by a dopamine shortage in the brain. Common dopamine agonists drugs includes.

Merapex,Neupro,Requip.

Serious Side Effects associated with dopamine agonist include low blood pressure dizziness when standing up hallucination and impulse control disorder such as pathological gambling compulsive eating and hypersexuality.

Dopamine antagonist

Theyare a class of drugs that bind to and block dopamine receptors. They turn down the activity which may be useful for the treatment of psychiatric conditions such as schizophrenia and bipolar disorder which have been associated with an overactive dopamine system. Many antipsychotic drugs are the antagonist working to block dopamine receptor in the brain. They are on dopamine receptors in the gastrointestinal tract may be used to treat nausea or as antiemetic to stop vomiting.

Dopamine antagonist drugs are

Thorazin, Reglan, Phenergan, Invenga, Clozaril.