Neurotransmitters
What are neurotransmitters and what do they do for the body?
Neurotransmitters are chemical messengers that carry body needs from neuron to neuron. Different neurons release different neurotransmitters. The soma of the neuron contains the nucleus where the DNA resides to direct synthesis. Neurotransmitters bind to receptors on dendrites that trigger membrane currents to promote or inhibit that electrical impulse generated in the cell body or the soma. The impulse travels down the axon to the terminal, where neurotransmitters are synthesized, stored, and released. Neurotransmitters are stored in small secs or vesicles in the axon terminal. Neurotransmitters affect behavior and common habits.
Dopamine
Dopamine is a natural neurotransmitter that controls mood, sleep, and learning. It regulates movement, emotion, motivation, and the feeling of pleasure or reward.
Serotonin
Serotonin is a natural neurotransmitter that controls mood and sleep. It affects mood, appetite, and pleasure.
The Influence of Drugs
Drugs are chemicals that affect the brain by tapping into its communication system and interfering with the way neurons normally behave. Some drugs mimic neurotransmitters and fool receptors, allowing the drugs to attach and activate neurons. Drugs leave abnormal messages throughout the neuron networking. For example, some drugs release abnormally large amounts of neurotransmitters or prevent the normal recycling of brain chemicals, disrupting communication. Drugs that mimic the receptor are called agonists. Drugs that block receptors or prevent reuptake are referred to as antagonists.
Drug interaction starts with the binding of an enzyme, a protein that catalyzes or aids in chemical reactions. To bind to an enzyme, receptor, or transporter, a drug must have a specific structure to fit into a protein. The protein exists in a conformation that will only allow bonds to form between the protein and the drug if the shape is correct. This is the lock-and-key method discussed previously. A drug must also be attracted to its target to be effective. A drug is attracted by intermolecular forces (IMFs) and must be attracted for a sufficient amount of time to influence the organism.
Classification of Drugs
Stimulants
Stimulants increase overall levels of neural activity. Many stimulants act as agonists of the dopamine neurotransmitter system. Stimulant users seek a euphoric high or a feeling of intense elation and pleasure. Stimulants can become physically and psychologically addicting.
Drugs
Cocaine
Amphetamines
Methamphetamines
Caffeine
Nicotine
Effects on the Body
Increased heart rate
Increased blood pressure
Increased body temperature
Effects When Used
Low Dosage:
Increased alertness, mild euphoria, and decreased appetite
High Dosage:
Increased agitation, paranoia, hallucinations, and heightened sensitivity to physical stimulants.
These drugs are addictive.
Caffeine
Caffeine is generally used to maintain increased levels of alertness and arousal. Caffeine targets adenosine activity. Adenosine is a neurotransmitter that promotes and encourages sleep. Since caffeine works to stop the feeling of sleepiness, caffeine is an adenosine antagonist. In its normal state, when our bodies are exhausted, there is an increase in adenosine molecules. The adenosine molecules bind to adenosine receptors in our brains, resulting in the transduction of sleep signals. Since the structure of caffeine is similar to that of adenosine, when it reaches the brain, caffeine can also bind to the adenosine receptor and block adenosine molecule from accessing it, thus disrupting sleep signals. By inhibiting the adenosine receptors, there are decreased levels of sleepiness and increased levels of wakefulness or alertness.
Caffeine, in itself, is not a harmful drug but high levels of caffeine can result in insomnia, agitation, muscle spasms, nausea, irregular heartbeat, and, in some cases, death. Limiting the use of stimulant drugs, like caffeine, may reduce the symptoms of sleeping disorders, like insomnia.
Nicotine
Once nicotine enters the bloodstream, all ganglionic neurons of the autonomic system (parasympathetic & sympathetic ganglia) are activated by nicotinic acetylcholine (ACh) receptors released from preganglionic fibers. ACh receptors on corresponding neurons are attracted to nicotine and enter through neuron ligand-gated ion channels. When the neurotransmitter releases and binds to the receptor, this channel opens and allows positive ions to cross the cell membrane. Nicotine mimics the feeling of arousal and reward within the nervous system.
Nicotine can be problematic to the cardiovascular system and may cause cardiovascular disease, stroke, and cancer. Nicotine will cause the vascular tone to become more sympathetic. There is no significant parasympathetic regulation of blood pressure causing the blood pressure to increase. Likewise, the cardiac muscle generates its own action potential due to the autonomic process, therefore, receiving conflicting signals can affect the rhythm of the heart.
Sedative-Hypnotics (Depressants)
Sedative-Hypnotics or depressants are drugs that tend to suppress the central nervous system. Depressants serve as agonists of the gamma-aminobutyric acid neurotransmitter system (GABA). These drugs have a quieting effect on the brain and can be used to treat anxiety and insomnia. Depressants can become physically and psychologically addicting.
Drugs
Alcohol
Barbiturates
Benzodiazepines
Effects on the Body
Decreased heart rate
Decreased blood pressure
Effects When Used
Low Dosage:
Increased relaxation, decreased inhibitions
High Dosage:
Induced sleep, motor disturbance, memory loss, decreased respiratory function, and death
These drugs are addictive.
Alcohol
Alcohol exhibits a quieting effect on the brain. It changes consciousness, reaction time, and visual activity. Alcohol mimics the gamma-aminobutyric neurotransmitter, acting as an agonist.
Alcohol may cause Alcohol Use Disorder (AUD), a chronic relapsing brain disease characterized by an impaired ability to stop or control alcohol use despite adverse social, occupational, or health consequences. Alcohol, like many other depressants, can grow tolerance and withdrawals may occur.
Opiates & Opioids (Prescription Drugs)
Opioids are drugs with analgesic properties, decreasing pain. They mimic the endogenous opioid neurotransmitter system which is where the body makes small quantities of opioid compounds that bind to opioid receptors reducing pain and producing euphoria. These drugs have a high possibility of abuse. Opiates are natural opioids, derived from opium. Opium is a naturally occurring compound in poppy plants.
Drugs
Opium
Heroin
Fentanyl
Morphine
Oxycodone
Vicodin
Methadone
Effects on the Body
Decreased pain
Pupil dilation
Decreased gut motility
Decreased respiratory function
Effects When Used
Pain relief, euphoria, sleepiness, and death
These drugs are addictive.
Hallucinogens
Hallucinogens are a class of drug that results in profound alternations in sensory and perceptual experiences. These drugs can become physically and psychologically addicting.
Drugs
Marijuana
LSD
Peyote
Mescaline
DMT
Dissociative Anesthetic
Ketamine
PCP
Effects on the Body
Increased heart rate
Increased blood pressure
(may dissipate over time)
Effects When Used
Mild to intense sensory and/or perceptual changes
These drugs are addictive.
Nonsteroidal Anti-inflammatory Drugs (NSAIDs)
Nonsteroidal anti-inflammatory drugs (NSAIDs) drugs are drugs that can be used to treat multiple symptoms. They reduce inflammation and are used to aid a large range of medical activities, such as an analgesic (pain reliever), or antipyretic (fever reducer).
Aspirin
Aspirin is a special classification of drug. Aspirin can work as an analgesic or pain reliever, antipyretic or fever reducer, and an anti-inflammatory agent or inflammation reducer. Aspirin, also known as acetylsalicylic acid, is produced through the reaction of acetic anhydride and salicylic acid.
For aspirin to work properly, aspirin needs to be in the bloodstream. The higher pH, the faster the aspirin tablet breaks apart and the faster it gets into the bloodstream.
Dopamine in relation to Stimulants
Dopamine follows the normal process of neurotransmission. Dopamine neurons synthesize dopamine by a series of reactions that take place in the neuron terminals. Electrical impulses trigger the release of dopamine into the synapse, dopamine binds to its corresponding receptor on the neighboring dendrites and alters membrane currents. After the dopamine binds, it comes off and can then bind to proteins for transportation on the releasing neuron to be taken back up into the neuron terminal.
Once dopamine is released into the synaptic space it is either transported back into the dopamine terminal by dopamine transport proteins as described above or oxidized by O₂, which diffused from the blood capillaries into the surrounding spaces.
Dopamine can be oxidized by monoamine oxidases, the catalyzation enzyme used to aid the degradation of other molecules. When dopamine concentrations rise, dopamine can be oxidized by O₂ without the help of any enzyme. This is known as the process of autooxidation.
In the presence of a stimulant, the stimulant causes the release of dopamine from the axon terminal into the synaptic space. The excess dopamine in the synaptic space binds to dopamine receptors on specific neurons to cause stimulation of certain pathways in the brain. This causes increased alertness and agitation. When high doses are used, dopamine accumulates in the synaptic space and the transporters become saturated. The transport proteins are unable to transport dopamine back inside the terminal. This excess dopamine becomes auto-oxidized.
The process of oxidation causes the structure of lipids, proteins, and DNA to become disorganized. Cross-linking of these molecules can form polymers, which can be detrimental to an individual’s health. Damaged proteins cannot perform their normal cell function, damaged DNA cannot participate in the synthesis of new proteins to keep the cell alive and damaged lipids become leaky and unusable. When this occurs, the cell will destroy itself to stop damage to the host.
The neurons of dopamine and serotonin are very vulnerable to oxidative damage. Dopamine neurons are found in pathways that control voluntary movement. Oxidative damage can cause movement deficiency. Drugs such as MDMA and Ecstacy can damage serotonin.
Drugs and the Brain
Drug delivery to the brain affects the likelihood of drug abuse. The faster a drug goes to the brain, the more likely it is to be addicting. Delivery methods, such as smoking, injecting and snorting, influence rates of delivery to the brain. Methods, genetics, and environment influence the potential of drug addiction. The faster way to deliver drugs to the brain is by smoking. An inhalant seeps into the lung blood and travels to the brain. A slower delivery, like ingestion, is less addicting.
Areas of the Brain Affected by Drug Abuse
The Brain Stem
The brain stem controls basic functions critical to life. Drug use and abuse affect functions like heart rhythm, breathing, and sleeping.
Cerebral Cortex
The cerebral cortex is divided into areas that control specific functions such as the processing of information from the senses. The frontal cortex is the thinking center of the brain where an individual processes plans, problem-solving, and makes decisions. Drug use and abuse will limit and damage the tissue and function of this important part of the brain.
Limbic System
The limbic system is the brain’s reward circuit. It links together structures that control and regulate the ability to feel pleasure and is activated by healthy, life-sustaining activities. This is also where emotion is processed. Drug use and abuse will hinder life-sustaining activities and alter the perception of emotion.
