Dopamine Antagonists

Blocking dopamine receptors through the antagonism of the receptors is a drug known as a dopamine antagonist. This drug works in the opposite way of a dopamine agonist, which stimulates rather than blocks dopamine receptors.

Dopamine, a neurotransmitter, is present in a number of animals as well as humans. It works by activating dopamine receptors. There are five recognized kinds of dopamine receptors in the human body, located in the central nervous system, the brain, the kidney, and blood vessels. These five types are known as D1, D2, D3, D4, and D5. Part of the G protein-coupled receptors family, dopamine receptors rest on the surface of a cell. They have the ability to sense molecules outside of the cell and signal a response. The signal-triggering chemical for dopamine receptors is dopamine.

Dopamine receptors play an important role in the neurological processes of pleasure, motivation, cognition, learning, memory, and movement, among others. Any impairment in the normal function of these receptors can have a mild to severe effect on a person’s physical and mental well-being. Among its many uses, a dopamine antagonist can treat conditions resulting from drug abuse through the blocking of dopamine receptors and the inhibiting of the reuptake of dopamine by these receptors.

How Receptor Antagonists Work

A receptor antagonist works by binding itself to dopamine receptors. In doing so, the drug dampens or blocks the ability of the receptors to receive dopamine. In other words, it effectively turns down dopamine activity. This disruption to the normal function of the receptors can be used to treat various disorders, such as schizophrenia, which is often associated with an overactive dopamine system.

Use of Dopamine Antagonists

Dopamine antagonists are primarily used as antiemetics, atypical antipsychotics, and tricyclic antidepressants.

* Antiemetics in the dopamine antagonist category include droperidol, metoclopramide, and domperidone. These medications are commonly used to treat nausea or vomiting. Side effects can include restlessness, muscle spasms, and drowsiness.
* Atypical antipsychotics include risperidone, clozapine, olanzapine, ziprasidone, and quetiapine. These medications are typically used to treat psychiatric conditions such as schizophrenia and bipolar depression. Side effects may include motor control disabilities, tardive dyskinesia (the permanent involuntary twitching of fine muscles, such as in the face), neuroleptic malignant syndrome, and increased threat of sudden cardiac death, stroke, diabetes, and blood clots.
* Tricyclic antidepressants include clomipramine and amoxapine. These drugs are frequently used to treat clinical depression, attention-deficit hyperactivity disorder, and chronic pain. Side effects associated with these medications include memory impairment, anxiety, drowsiness, sexual dysfunction, and irregular heart rhythms, but a tolerance to most adverse effects develops in people who continue treatment.

Adverse Effects of Dopamine Antagonists

Side effects associated with dopamine antagonists include:

* Hyperprolactinaemia
* Parkinsonism
* Impotence
* Tardive dyskinesia
* Menstrual dysfunction
* Galactorrhea
* Low libido

Dopamine Antagonist Drugs

Common dopamine antagonists include:

* Acepromazine
* Amoxapine
* Benperidol
* Butaclamol
* Chlorpromazine
* Clopenthixol
* Droperidol
* Flupenthixol
* Fluspirilene
* Iodobenzamide
* Mesoridazine
* Metoclopramide
* Nemonapride
* Perazine
* Pimozide
* Promazine
* Remoxipride
* Spiperone
* Stepholidine
* Sultopride
* Thiethylperazine
* Thiothixene
* Trifluoperazine
* Triflupromazine
* Ziprasidone

Regulation of Dopamine

Our physical and mental health can be mildly to greatly affected by the regulation of dopamine. Antipsychotics and stimulants can cause normally stable dopamine receptors to suffer a reduction, or increase. This is commonly referred to as down-regulation or up-regulation, respectively.

When dopamine receptors are repeatedly stimulated through drug use, the number of receptors decreases. The receptors that remain can become less sensitive to dopamine, in a process known as desensitization. Drug users know this process as drug tolerance, when the repeated use of the same quantity of a drug causes less of a response than prior use.

Drug abusers are prone to suffering from impaired dopamine activity. Repeated drug use or drug addiction can disrupt the reuptake system, the body’s natural recycling of dopamine. When the body is unable to maintain regular levels of dopamine, consequences such as a change in normal emotional responses or worse, may follow.

Dopamine and Drug Use

The chief chemical involved in the brain’s reward pathways is dopamine. Drugs such as cocaine and amphetamine can affect dopamine function either through the stimulation or the blocking of dopamine receptors. By changing the flow of dopamine, these drugs produce their pleasurable effects.

Amphetamine and cocaine produce similar effects on drug-takers. Yet these effects are achieved through very different processes. Cocaine increases dopamine levels by preventing the reuptake of dopamine. It does this by attaching itself to the proteins that would usually carry dopamine. Furthermore, it hangs onto these proteins for a greater time period than dopamine.

This not only affects the body’s normal recycling of dopamine, but the level of dopamine in the synapse. The result is a surplus of dopamine that stimulates neurons, creating prolonged feelings of excitement. Similarly, amphetamine increases dopamine levels. However, it does this by boosting the release of dopamine rather than preventing dopamine reuptake.

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