Neurobiology of Intoxication, Reward and Tolerance

RewardAs stated earlier, neurobiology is the study of cells of the nervous system and how these cells are organized of these cells into functional circuits that process information and influence behavior. Neurobiology is a sub unit of both biology and neuroscience. Neuroscience is much broader as a scientific study of the nervous system than neurobiology. Neurobiology helps us to understand how the neurons are affected by whatever we ingest. The neurons as you and me now know are very crucial as they are the chemical messengers that transmit signals to initiate certain crucial responses. However these neurons are often affected by drugs of abuse that in most cases depletes them rendering them incapable to function normally. As studied earlier in our brain there are different neurotransmitters that perform different purposes to ensure that all functions of the brain are well attended to. There are inhibitory neurotransmitters as well as excitatory neurotransmitters and the balance between these neurotransmitters must be achieved for better functioning of the brain but these drugs of abuse interferes with these balance by causing depletion of certain neurotransmitters creating an imbalance between the different categories of the neurotransmitters in the brain. In this article we try to find out how intoxication, reward and tolerance come about to users of alcohol and other drugs.


According to World Health Organization (WHO) intoxication is a condition that follows the administration of a psychoactive substance and results in disturbances in the level of consciousness, cognition, perception, judgment, affect, or behavior, or other psychophysiological functions and responses. The disturbances are related to the acute pharmacological effects of, and learned responses to, the substance and resolve with time, with complete recovery, except where tissue damage or other complications have arisen. They further explain that the term intoxication is a term that is commonly used in alcoholism and is the same in meaning to the common term drunkenness. Alcohol intoxication manifests in such symptoms as slurred speech, unsteady gait, disorderly conduct, impaired judgment, slowed reactions, loss of memory, vomiting, euphoria and insensibility among others. Alcohol has contents of ethanol among other fermented stuff. When taken ethanol will produce its depressive effects on certain areas of the brain resulting in physical and mental impairments. These problems will continue as the level of alcohol consumption is increased, therefore more alcohol means more intoxication.

Here is what happens in the brain

When alcohol is taken it increases the effect of the body’s naturally occurring neurotransmitter gamma amino butyric acid (GABA). As I mentioned earlier neurotransmitters are substances that chemically connect the signals from one nerve to the next allowing a signal to flow along a neural pathway. An inhibitory neurotransmitter (alcohol) reduces this signal flow in the brain. This explains how alcohol depresses both a person’s mental and physical activities. When you take alcohol 20% of ethanol will be absorbed into the bloodstream from the stomach while 80% is absorbed from the small intestines. However the more the ethanol stays in the stomach the slower it is absorbed into the bloodstream and the lower the peak in blood alcohol concentration. This is why when a person takes alcohol with empty stomach he will be intoxicated within such a short time. The food in the stomach normally slows the rate of alcohol absorption lowering the peak in blood alcohol concentration.

The reward system

The reward system is mainly dominated by the excitatory neurotransmitter known as dopamine. This hormone gives the brain its ‘high’, the euphoric feelings that is commonly sought by people who use drugs of recreation. Close to all addictive drugs directly or indirectly target the brain’s reward system by flooding the circuit with dopamine. Dopamine is a neurotransmitter present in regions of the brain that regulate movement, emotion, cognition, motivation, and feelings of pleasure. The overstimulation of this system, which rewards our natural behaviors, produces the euphoric effects sought by people who use drugs and teaches them to repeat the behavior. The persistent release of dopamine during chronic drug use progressively recruits limbic brain regions and the prefrontal cortex, embedding drug cues into the amygdala through glutaminergic mechanisms and involving the amygdala, anterior cingulate, orbitofrontal cortex, and dorsolateral prefrontal cortex in the obsessive craving for drugs Despite dopamine being the dominant neurotransmitter in the reward system there are also other neurotransmitters that work to modulate both the reward system and the psychomotor effects of addictive drugs. However there is still little literature to support this and so dopaminergic system is still the biggest consideration when reward system is to be tamed. Naturally the balance between the excitatory neurotransmitter and the inhibitory neurotransmitters enables proper functioning of the brain but with drugs the drugs will suppress the inhibitory neurotransmitters flooding the brain with dopamine which is the fuel behind reward.

RewardUnderstanding tolerance

Tolerance refers to a situation when a person ceases to react to a drug in initial doses and therefore higher dosage is needed for the effects to be achieved. This normally happens when a person has been using the drugs for a long time. This is common in the use of opioids in pain management, the patient will cease to respond to initial dosages and therefore need higher dosages to calm the pain. For example, morphine is often used for pain. It works by binding to opiate receptors where it triggers the inhibition of an enzyme called adenylate cyclase that orchestrates several chemicals in the cell to maintain the firing of impulses. After repeated activation of the opiate receptor by morphine, the enzyme adapts so that the morphine can no longer cause changes in cell firing. Therefore higher dosages will have to be administered for the pain to be calmed.

Finally, Dr. Dalal Akoury (MD) of AWAREmed Health and Wellness Resource Center is committed to helping all people trapped in drug addiction. Call on her today at Myrtle Beach, South Carolina for help.

Neurobiology of Intoxication, Reward and Tolerance