Neurotransmitters and the effect of recreational drugs

What are neurotransmitters?

Chemical messengers that act between the neurons in the brain. This allows the brain to process thoughts and memories by sending messages around the brain.

Neurotransmitters can either send or inhibit messages from being sent.

How do neurotransmitters work?

They are released into the synaptic cleft and taken up by the receptors on dendrites of another neuron. This causes a message to be sent from one neuron to the next. Alternatively, neurotransmitters can also stay in the synaptic gap or a re-used in the pre-synaptic neuron through the reuptake process.

What is the function of the neurotransmitter noradrenaline / norepinephrine?

Regulates arousal, attention, cognitive function and stress reaction. Controls emotion, mood and sleep.

What is the function of the neurotransmitter dopamine?

Provides a feeling of pleasure, satisfaction and motivation. Regulates mood.

What is the function of the neurotransmitter serotonin?

Involved in mood, sleep, digestion, nausea, wound healing, blood clotting and sexual desire.

What is the function of the neurotransmitter acetylcholine?

Involved in muscle contractions to move muscles. Helps with learning, memory, attention and arousal.

What are recreational drugs?

Drugs used in the absence of medical grounds, often taken by users for personal enjoyment.

Why are recreational drugs referred to as psychoactive drugs?

Because they altar braun function, which changes our mood, perception and conscious experience.

How do drugs work in relation to neurotransmitters?

Some drugs mimic the role of a neurotransmitter and can bid to receptor sites of post-synaptic neurons in order to increase neurotransmitter functions, whilst others can cause the neurons to release large amounts of natural neurotransmitters or prevent the normal recycling of these brain chemicals by interfering with brain transporters.

Explain the reward pathway

It is located in the limbic system of the brain, involving several other parts of the brain including the ventral tegmental area (VTA) and nucleus accumbens. When activated by a rewarding stimulus, the reward pathway creates the experience of pleasure, increasing the dopamine release into the prefrontal cortex, encouraging the behaviour to be repeated to recreate the reward. Drugs hijack this system in humans.

How do recreational drugs hijack the reward pathway?

Drugs act by changing the way neurotransmitters operate in the brain. Most psychoactive drugs of addiction work on the limbic system. The drug increases the amount of dopamine in the reward pathways by boosting the activation of dopamine synapses, causing an intensely pleasurable experience or a feeling of euphoria. However, this causes the brain to produce less dopamine (down-regulation), so when the drug wears off the person now has less dopamine than they would have for normal functioning. This causes dysphoria. Repeated use occurs to avoid withdrawal for the lack of dopamine produced by the brain and so leads to addiction. Gradually, more of the drug needs to be taken for the user to have the same experience as the first time - they build a tolerance.

What is heroin’s mode of action?

It is an agonist drug with a depressant effect on the nervous system. It binds with receptors of our natural opioids, like endorphins, and enhances our natural responses. This triggers reward pathways.

What is PCP’s mode of action?

PCP acts as an antagonist as blocks glutamate NMDA receptors, leading to hallucinations. It affects memory and our ability to process information. High doses cause hallucination, whilst low doses have similar affects to alcohol intoxication.

What is cocaine’s mode of action?

Acts as an agonist drug. Increases activity in the dopamine pathway by blocking the reuptake of dopamine. This leads to a surplus of dopamine, causing a euphoric ‘high’. Increases energy and motor activity.

What are agonist drugs?

Drugs which mimic or increase the neurotransmitter effects by occupying and stimulating the postsynaptic receptor sites.

What are antagonist drugs?

Drugs which occupy and block receptor sites to prevent the neurotransmitter from binding, so they reduce the neurotransmitter effects (but not enough to stimulate the receptor).

Strength of the theory?

There is supporting evidence for the arguments of drug effects in the brain. Olds and Milner (1954) found a pleasure centre in the brains of rats. The rats were given tiny jolts of current through electrodes, providing a ‘high’ in the rats. It was found that the rats would repeatedly press the lever do provide this current up to 2000 times an hour, proving the effects of drugs on the brain.

Real life application of the theory?

Knowledge that heroin binds to opioid receptors has led to the creation of Naloxone (an addiction replacement drug). This drug does not produce the feeling of euphoria like heroin, but can help manage withdrawal symptoms, allowing the brain’s dopamine receptors to return to a normal level of functioning.

Weakness of the theory?

Drug treatments created from this idea only tackle the neurobiology of drug addiction and oversimplify the complex process of addiction. Humans use recreational drugs to regulate mood and emotions. Neurobiological explanations ignore motivations for drug use - the theory is considered reductionist. Therefore, if the user does not want to quiet, they will not be able to quiet even with drug replacement therapies.