This article was written by our trainer Maria Vittoria Zulli
The brain and neurotransmitters
The brain is composed of billions of cells called neurons, which are organised into circuits and networks that work together to coordinate and perform specific functions. Each neuron acts as a switch, regulating the flow of information in the brain. To communicate, neurons release neurotransmitters (chemical messengers) which are passed from neuron to neuron among different parts of the brain, spinal cord, and peripheral nervous system. These neurotransmitters bind to specific receptors on target neurons, producing a variety of effects that enable the brain to function as a cohesive unit.
Depending on the specific neurotransmitter, they can exert their effects by either exciting or inhibiting the target neuron. Excitatory neurotransmitters excite the neuron, resulting in more neuronal activation as the chemical message is passed along to other neurons. On the contrary, inhibitory neurotransmitters block or prevent the chemical message from being passed along.
Some of the well-known neurotransmitters include
1. Dopamine: involved in regulating motivation, pleasure, reward, learning and motor control.
2. Serotonin: regulates mood, behaviour, memory, appetite, and sleep
3. Norepinephrine: involved in the fight or flight response and regulating arousal and attention.
4. Endorphins: regulate pain, pleasure, and stress.
5. Glutamate: involved in learning and memory and is the most abundant neurotransmitter in the brain.
Neurotransmitters are essential in maintaining brain health and shaping everyday life and function. Without neurotransmitters, neurons would not be able to communicate with each other, and the nervous system would not be able to perform its various functions, such as controlling movement, regulating emotions, processing sensory information, and coordinating thoughts and behaviours. Disruptions in neurotransmitter function have been linked to various neurological and neurodegenerative disorders, such as Parkinson’s disease, Depression and Schizophrenia (Teleanu et al., 2022).
How do recreational drugs affect neurotransmitter function?
Recreational drugs significantly impact the brain’s chemistry and how individuals perceive and interact with their environment. These substances have the ability to modify neurotransmitter systems in the brain in various ways, leading to altered brain function and behaviour. For instance, some recreational drugs can enhance or inhibit the release of neurotransmitters like dopamine or serotonin, causing the central nervous system to either slow down or speed up. Other drugs can mimic the action of neurotransmitters at receptor sites or block their reuptake, resulting in intensified effects and altering the balance of neurotransmitters in the brain (Tomkins et al., 2001).
For example, drugs such as cocaine and amphetamines work by increasing the levels of dopamine in the brain, producing feelings of pleasure and reward (Ashok et al., 2017). Other drugs, such as heroin and morphine, mimic the action of endorphins, which are naturally occurring painkillers in the body. Even though they mimic endorphins, they don’t activate neurons in the same way, leading to abnormal messages being sent through the network. Tetrahydrocannabinol (THC), the primary psychoactive component in marijuana, binds to cannabinoid receptors in the brain, which can alter the release of neurotransmitters such as dopamine.
During the early stages of drug usage, neurotransmitters normalise when intoxication wears off. However, repeated drug misuse can lead to long-term changes in the function of neurotransmitter systems, which can contribute to the development of addiction and other mental health disorders such as depression and anxiety (Volkow et al., 2010).
Parts of the brain affected by drug use
Different types of recreational drugs can affect different parts of the brain. The specific effects can vary depending on factors such as the dose of the drug, duration of use, and individual differences in brain chemistry and genetics. However, here are the most common brain regions that are known to be affected by drug use:
The prefrontal cortex (PFC) is involved in a variety of higher-level cognitive functions and executive functions, such as decision-making, judgement, impulse control, working memory, attention and modulation of social behaviour. Recreational drug use can impair these functions and lead to impulsive behaviour and poor decision-making. This can contribute to drug-seeking behaviour and difficulty quitting drug use. Additionally, the PFC plays a role in regulating the activity of the limbic system, which is involved in reward processing and emotion regulation. Disruption in PFC function can lead to dysregulation of the limbic system, contributing to the development and maintenance of drug addiction (Goldstein & Volkow, 2011).
The Limbic System is a set of interconnected brain structures involved in processing emotions, memories, and arousal. It is referred to as the brain’s reward centre and is mainly comprised of
● The amygdala: responsible for processing emotions and regulating the brain’s reaction to stress and negative emotions like fear and anxiety. The amygdala is implicated in the process of reward learning and memory, conditioned reward, emotion dysregulation related to drug use, and the transition to addiction (Kilts, 2001). Chronic exposure to drugs of abuse has been shown to disrupt the pathways that project from the amygdala to the PFC (Dafny et al., 2017). Recreational drug use can alter the function of this region and lead to anxiety and mood disorders.
● Hippocampus: plays an essential role in learning and memory. It is involved in the formation, consolidation, and retrieval of new memories, including episodic, spatial, and contextual memories. Recreational drug use, particularly long-term use, can impair these functions and lead to significant impairments in memory and cognitive function (Kutlu et al., 2016). Additionally, most drugs of abuse, such as opiates and psychostimulants, suppress hippocampal neurogenesis, the process by which new neurons are formed in the brain (Dafny et al., 2017)
● Thalamus: relays sensory and motor information to the cortex and regulates consciousness, sleep, and alertness. It is also involved in the processing of emotional and motivational information. Studies have shown that the thalamus may play a role in drug addiction by mediating the rewarding effects of drugs (Huang et al., 2018). Recreational drugs can affect thalamic function by altering pain perception, sensory and motor processing and leading to cognitive deficits (Zhang et al., 2016).
● Hypothalamus: regulates the autonomic nervous system, the endocrine system, and basic survival functions such as hunger, sleep, thirst, stress and body temperature. Recreational drugs can affect the hypothalamus in various ways, leading to changes in these physiological processes (Zhang et al., 2019).
● Nucleus Accumbens: integrates information from cortical and limbic structures to mediate goal-directed behaviours (Scofield et al., 2016). It is also involved in reward, pleasure and addiction and plays an important role in reinforcing behaviours associated with natural rewards, such as food. Recreational drugs activate the dopamine system in the nucleus accumbens, leading to a surge of dopamine release. This flood of dopamine produces feelings of pleasure and reinforces drug-seeking behaviour, leading to drug addiction. Chronic drug use can lead to long-term changes in the nucleus accumbens, altering the brain’s reward system and making it more difficult for an individual to experience pleasure and reward from natural sources (Dafny et al., 2017).
● Cingulate gyrus: involved in various functions, including emotion, motivation, pain perception and decision-making. It plays a crucial role in reward processing, which is closely related to drug addiction. Studies have shown that the cingulate gyrus is activated in response to drug-related cues and stimuli, indicating its involvement in drug-seeking behaviour (Goldstein et al., 2002). Chronic drug use has been associated with changes in the structure and function of the cingulate gyrus, affecting its optimal functioning (Goldstein et al., 2002).
The ventral tegmental area (VTA) is part of the dopaminergic reward pathway in the brain and is closely connected to and interacts with several limbic system structures, including the nucleus accumbens, amygdala, and prefrontal cortex. It is primarily involved in reward processing and reinforcement learning and contains a high concentration of dopaminergic neurons that project to several regions in the brain, including the prefrontal cortex (Morales et al., 2017). Most recreational drugs directly or indirectly affect the activity of dopaminergic neurons in the VTA, leading to increase dopamine release in other brain regions. This increase in dopamine release is thought to be a major contributor to the pleasurable effects of these drugs and can lead to addiction with chronic use (Kauer, 2004).
Full list of references for this article can be found here