Dopamine is a neurotransmitter associated with the sense of pleasure. The neural cells start producing dopamine in response to reward. Hence, it is also called the reward center of the brain. Dopamine not only works in giving us a sense of pleasure, but it also acts as a vasodilator regulating the blood vessels and blood flow for proper circulation.
The dopamine effects are NOT responsible for one’s addiction.
The well-known cells involved in the release of dopamine are present in the ventral tegmental area (VTA). In the events of drug use or when something unexpected happens, the cells activate and produce dopamine into the extracellular regions. This release eventually leads to addiction due to a chain of reactions. A cluster of cells in the cerebral cortex region involved in dopamine release in the nucleus accumbens.
What are the effects of dopamine alterations?
If the individual has a low concentration of dopamine, he/she is prone to conditions like Parkinson’s disease. The condition arises when the cells in the substantia nigra associated with the synthesis of dopamine die. The patients are administered with Levodopa (L-dopa), which is a precursor of dopamine. This L-Dopa can help the patients regenerate the amount of dopamine, leading to improved symptoms.
Increased amounts of dopamine in the brain causes hallucinations, and a chronic condition can also result in schizophrenia. Schizophrenic individuals take dopamine inhibitors as a part of the treatment, not because it is the reward center, but because the individuals are sensitive to the effects of dopamine.
Dopamine effects on unpleasant events?
In cases of an unpleasant situation, some neurons deactivate or suppress due to the inhibitory activity. In a study, the researchers observed that few cells in the VTA region shut down or have no response to the stimulus. Since memory and learning are also a few functions of dopamine, dopamine inhibition can impair learning in an individual.
In a later study, they concluded that the cells in the dorsal VTA shut down while the cells in the ventral VTA are still producing the neurotransmitter. The production is so profound that a ‘burst firing’ is also observed. Whereas, the cells in the dorsal VTA regain their activity after the person is over the incident. With this retaining activity, people learn and remember the experience of an unpleasant event.
Is compulsive alcohol or drug-use an effect of dopamine addiction?
There is a misconception that dopamine is responsible for one’s addiction to drug-use or alcohol intake. People still believe this myth because dopamine is released when one feels a sense of pleasure. You should be well-informed that Dopamine release is one of the events with drug use or alcohol intake. Opioids, oxytocins, serotonin, and other hormones together drive a sense of pleasure.
Dopamine acts as a motivator to seek the substance or object that produces such an effect.
Factors like what triggered its release– drug use, alcohol, chocolate, or a person at that moment– play a vital role. The individual with the motivation from dopamine is out now to seek the same experience. Doing the activity again keeps them happy and satisfied, but overloads the system. Social influence, genes, and family history can also influence the subject.
Drug abuse can also attack the PFC, (the basis of decision-making, judgment, and other executive functions) resulting in cognitive deficits. Its role is to send inhibitory signals to the VTA. Unfortunately, poor judgment is predisposed to compulsive drug-taking behavior. This predisposition suggests a lack of control and increased severity with drug abuse. Moreover, recent studies suggest low levels of GABA (carrier of inhibitory signals) in addiction.
What is the reason for one’s addiction?
Pleasure is the key to addiction. Dopamine gives a sense of pleasure along with learning and memory. Note that learning and memory are two key elements that change a person from the state of likeness to addiction.
Dopamine also interacts with glutamate. Basic human instincts of survival- like eating and sex involve glutamate. The glutamate neurons are excitatory and provoke the VTA to release excess dopamine. It also acts as a reward center for motivation. The motivation with reward and the sense of pleasure is what increases the feeling of likeness to wanting it, eventually getting addicted to it.
Addiction during the 1980s was believed to be due to a lack of willpower. Addicted individuals were punished until they break the habit. But now, addiction is a chronic disease condition. It hijacks the brain. The effect is not only due to drug use, but it can also be due to shopping, gambling, and food– among which sugar addiction is common.
What is the underlying mechanism of addiction?
When a person experiences a sense of pleasure, the dopamine releases into the extracellular region. It attaches to the D2 dopamine receptors. Without any drug use, the release of dopamine is 5 Hz- the baseline steady-state. With a drug, the dopamine release increases to 30 Hz. Drugs like cocaine, block the dopamine transporters– responsible for sending the extracellular dopamine back into the neuron.
Additionally, drugs like methamphetamine can enter the neuron and stimulate the release of dopamine. As a result, the concentration of extracellular dopamine increases resulting in tolerance.
Dopamine effects on addiction to drugs
The addiction to a drug increases with its reinforcing effects on the release of dopamine. The faster it induces the release, the more is the saliency. The reward a person attains after intense hard work with time and effort can also induce the release. But, the release due to this reward is prolonged.
Addictive drugs release dopamine 100 times faster than the award. The release is also reliable with drug use. People prefer the intravenous or inhalation route of administration of a drug because it is the quickest way of transfer to the brain than swallowing a pill.
The use floods the nucleus accumbens with dopamine—the hippocampus present near the cluster stores the memory of satisfaction. The hippocampus, along with the amygdala, is responsible for a conditioned response and intense craving. The glutamate pathway produces little DA from VTA in the resting phase.
However, exposure to cue sufficiently activates the glutamate pathway. Addicts can relapse to the drug after watching a hypodermic needle or relapse to alcohol after seeing a bottle of whiskey, even after years of abstinence.
What happens due to long term use?
The dopamine release is the same in both addicts and non-addicts. But the drive to continue the drug intake is not the same. With more drive, comes long term intake.
With long-term use of a drug or alcohol, the dopamine content increases gradually in the system. To compensate for the impact, the system reduces D2 receptors.
This compensation results in an increased intake to experience the same results as before due to tolerance. The person takes in large quantities despite the consequences.
In contrast, with long-term use in a few individuals, the sensitivity and interest towards the drug decrease. They start to shift from taking drugs to feel high to taking drugs to feel normal. The orbitofrontal cortex and Central gyrus in the brain are responsible for inhibitory activity. Its activity is typical in a healthy person and reduced in addicts.
Dopamine modulations can alter their inhibitory activity, resulting in loss of control and more drug intake. However, exposure to conditions is the key to relapse after months of abstinence.
