Consequently, they have different effects on behaviour, different rates of development of tolerance, different withdrawal symptoms , and different short-term and long-term effects. Cannabis , though classified in the present study as a hallucinogen , also displays characteristics of depressants and stimulants.
Despite their differences, psychoactive drugs do share similarities in the way they affect regions of the brain involved in motivation, which is relevant to the development of drug dependence. This summary is free and ad-free, as is all of our content. You can help us remain free and independant as well as to develop new ways to communicate science by becoming a Patron!
Home » Psychoactive Drugs » Level 2 » Question 3. Previous Question. Next Question. For example, in mice, cocaine alters important genetic transcription factors and the expression of hundreds of genes. Other changes, such as proliferation of new dendrites branchlike structures on neurons that feature neurotransmitter receptors on their surface may be compensatory. Some epigenetic changes can be passed down to the next generation, and one study found that the offspring of rats exposed to THC—the main psychotropic component of marijuana—have alterations in glutamate and cannabinoid receptor formation that affects their responses to heroin.
Some drugs are toxic to neurons, and the effect accumulates with repeated exposures. Similarly, methamphetamine damage to dopamine-releasing neurons can cause significant defects in thinking and motor skills; with abstinence, dopamine function can partially recover , but the extent to which cognitive and motor capabilities can recover remains unclear.
To determine whether a drug affects a particular neurotransmitter system, or how, researchers typically will compare animals or people who have a history of drug exposure with others who do not. In experiments with animals, drug exposure often takes place under laboratory conditions designed to mimic human drug consumption.
Studies can be divided into those in which measurements are made in living animals or people and those in which animal brain tissue is removed and examined. Scientists may perform chemical assays on brain tissue to quantify the presence of a neurotransmitter, receptor, or other structure of interest. In a recent experiment, scientists assayed brain tissue from day-old rat pups and found that pups that had been exposed to nicotine in utero had fewer nicotinic acetylcholine receptors in the reward system than unexposed rats.
Scientists place the tissue in a laboratory solution of nutrients cell culture that enables neurons to survive outside of the body. The researchers may then, for example, add the drug being investigated to the solution and observe whether or not the neurons respond by increasing their release of neurotransmitters.
In both living animals and extracted tissue, the techniques for measuring neurotransmitter quantities and fluctuations include microdialysis and fast-scan cyclic voltammetry FSCV. Microdialysis involves taking a series of samples of the intercellular fluid containing the neurotransmitter through a microscopic tube inserted into the tissue or living brain.
FSCV, which was developed by NIDA-funded scientists, monitors neurotransmitter fluctuations at tenth-of-a-second intervals by measuring electrical changes related to neurotransmitter concentrations. A common design for experiments with either animals or people is to give study subjects a chemical that has a known effect on a particular neurotransmitter, and then observe the impact on behavior.
Typically, the chemical is either an agonist promoter or antagonist blocker of signaling by the neurotransmitter. Another team using a similar strategy showed that nicotine-induced disruption of glutamate signaling contributed to aspects of nicotine withdrawal. Both findings point to manipulation of the glutamate system as a potential strategy for treating some addictions. Researchers are now attempting to parlay this discovery into a novel treatment for cocaine addiction.
Brain imaging techniques enable neuroscientists to directly assess neurotransmission in people and living animals. With positron emission tomography PET , researchers can compare people with and without a drug addiction, quantifying differences in their levels of a particular neurotransmitter e. The findings indicated that the need to saturate these receptors is the primary driver of smoking behavior, but that sensory aspects of smoking, such as handling and tasting cigarettes, also play a role.
Or, they can elicit a drug-related behavior or symptom e. Researchers use several imaging techniques, including PET, functional magnetic resonance imaging fMRI , and computerized tomography to monitor metabolic activity in selected regions of the brain. Because each neurotransmitter has a unique distribution among the regions of the brain, information on locations of heightened or decreased activity provides clues as to which neurotransmitter is affected under the conditions of the study.
Another technique, diffusion tensor imaging, provides information about the white matter neuron fiber pathways through which sending neurons extend to receiving neurons, often over long distances.
Studies that link genetic variants to contrasting responses to drugs and drug-related behaviors provide another avenue of insight into drugs and neurotransmission. Such studies have shown, for example, that one rare variant of the gene for the mu opioid receptor is twice as common in the general population of European Americans as it is among European Americans who are addicted to cocaine or opioids. The finding suggests that receptors that are built based on the DNA sequence of the variant gene confer resistance to those addictions.
Another study linked a different variant of the same mu opioid receptor gene to reduced incidence and severity of neonatal abstinence syndrome among infants born to mothers who used opioids while pregnant. In another type of study, researchers knock down or knock out specific genes in laboratory animals and observe whether drug-related behavior—for example, pacing restlessly after being given a stimulant—increases or decreases.
Researchers have used this technique to explore how different subtypes of nicotinic acetylcholine receptor influence smoking behaviors, including how much a person smokes and susceptibility to symptoms of nicotine withdrawal.
Finally, researchers may implant modified genes into animals. In one such project, researchers, starting from clues provided by a South American caterpillar that eats coca leaves, modified the dopamine transporter gene to produce a transporter that is insensitive to cocaine. Mice who were implanted with this gene showed no preference for the drug over a saline solution.
This result could point researchers toward medications capable of preventing or treating cocaine use disorders. Research on cocaine illustrates how a drug can disrupt neurotransmission in multiple ways to promote intensified drug use, dependence, and addiction. Like all drugs that cause dependence and addiction, cocaine alters dopamine signaling. Studies, mostly with animals, indicate that the interactions of cocaine with the dopamine and other neurotransmitter systems influence the risk of drug use, progression to addiction, and relapse after abstinence through a variety of pathways.
By altering neurotransmission, drugs can produce effects that make people want to use them repeatedly and induce health problems that can be long lasting and profound. Some important effects are shared by all drugs that cause dependence and addiction, most prominently disruption of the dopamine neurotransmitter system that results in initial pleasurable feelings and, with repeated use, potential functional and structural changes to neurons.
There are also drug-specific effects: Each drug disrupts particular neurotransmitters in particular ways, and some have toxic effects on specific types of neurons. In America, more than people die every day from overdosing on opioids, according to the National Institute on Drug Abuse. Opioids are highly addictive, whether they are illicit drugs like heroin or prescription pain killers. These drugs are called opioids partly because they activate the opioid receptors on nerve cells, mimicking the effects of pain-relieving chemicals that would otherwise be produced naturally.
Opioids, though, also release high levels of dopamine, leading to the intense feelings of euphoria and pleasure caused by other drugs. Opioids are particularly addictive because long-term use changes the way nerve cells work in the brain ; even when someone is taking them as prescribed to treat pain.
They primarily affect the neural circuits in the brain that produce serotonin a neurotransmitter and produce perception-altering effects in the user. These experiences are unpredictable and vary from person to person.
While these drugs do not produce the physical symptoms of withdrawal and addiction that opioids, stimulants, and depressants cause, they do significantly alter the way the brain works. Long-term effects of hallucinogens include persistent visual disturbances flashbacks , disorganized thinking, paranoia, and mood disturbances.
Flashbacks formally termed Hallucinogen Persisting Perception Disorder , produce intense hallucinations that are nearly impossible to predict. It constricts blood vessels, dilates pupils, and increases body temperature, heart rate, and blood pressure.
It can cause headaches, abdominal pain, and nausea. Since cocaine also tends to decrease appetite, chronic users may become malnourished. The faster the drug is absorbed into the bloodstream and delivered to the brain, the more intense the high.
Injecting or smoking cocaine produces a faster, stronger high than snorting it. However, the faster the drug is absorbed, the faster the effects subside.
In order to sustain the high, the user must administer the drug again, which may lead to frequent use, often in higher doses, over a short period of time National Institute on Drug Abuse, a. Cocaine has a safety ratio of 15, making it a very dangerous recreational drug. An amphetamine is a stimulant that produces increased wakefulness and focus, along with decreased fatigue and appetite. Amphetamines are used in prescription medications to treat attention deficit disorder ADD and narcolepsy, and to control appetite.
Some brand names of amphetamines are Adderall, Benzedrine, Dexedrine, and Vyvanse. Meth is a highly dangerous drug with a safety ratio of only Although the level of physical dependency is small, amphetamines may produce very strong psychological dependence, effectively amounting to addiction. Continued use of stimulants may result in severe psychological depression. MDMA is a very strong stimulant that very successfully prevents the reuptake of serotonin, dopamine, and norepinephrine.
In contrast to stimulants, which work to increase neural activity, a depressant acts to slow down consciousness. A depressant is a psychoactive drug that reduces the activity of the CNS. Depressants are widely used as prescription medicines to relieve pain, to lower heart rate and respiration, and as anticonvulsants. Depressants change consciousness by increasing the production of the neurotransmitter GABA and decreasing the production of the neurotransmitter acetylcholine, usually at the level of the thalamus and the reticular formation.
The most commonly used of the depressants is alcohol , a colorless liquid, produced by the fermentation of sugar or starch, that is the intoxicating agent in fermented drinks Figure 6. Alcohol is the oldest and most widely used drug of abuse in the world. In low to moderate doses, alcohol first acts to remove social inhibitions by slowing activity in the sympathetic nervous system. In higher doses, alcohol acts on the cerebellum to interfere with coordination and balance, producing the staggering gait of drunkenness.
At high blood levels, further CNS depression leads to dizziness, nausea, and eventually a loss of consciousness. Alcohol use is highly costly to societies because so many people abuse alcohol and because judgment after drinking can be substantially impaired. Even people who are not normally aggressive may react with aggression when they are intoxicated.
Alcohol use also leads to rioting, unprotected sex, and other negative outcomes. When people are intoxicated, they become more self-focused and less aware of the social situation. As a result, they become less likely to notice the social constraints that normally prevent them from engaging aggressively, and are less likely to use those social constraints to guide them. For instance, we might normally notice the presence of a police officer or other people around us, which would remind us that being aggressive is not appropriate.
But when we are drunk, we are less likely to be so aware. The narrowing of attention that occurs when we are intoxicated also prevents us from being cognizant of the negative outcomes of our aggression. Alcohol also influences aggression through expectations.
If we expect that alcohol will make us more aggressive, then we tend to become more aggressive when we drink. Barbiturates are depressants that are commonly prescribed as sleeping pills and painkillers.
In small to moderate doses, barbiturates produce relaxation and sleepiness, but in higher doses symptoms may include sluggishness, difficulty in thinking, slowness of speech, drowsiness, faulty judgment, and eventually coma or even death Medline Plus, Related to barbiturates, benzodiazepines are a family of depressants used to treat anxiety, insomnia, seizures, and muscle spasms.
In low doses, they produce mild sedation and relieve anxiety; in high doses, they induce sleep. In the United States, benzodiazepines are among the most widely prescribed medications that affect the CNS. Toxic inhalants are also frequently abused as depressants. These drugs are easily accessible as the vapours of glue, gasoline, propane, hairspray, and spray paint, and are inhaled to create a change in consciousness.
Inhalants are some of the most dangerous recreational drugs, with a safety index below 10, and their continued use may lead to permanent brain damage. Opioids are chemicals that increase activity in opioid receptor neurons in the brain and in the digestive system, producing euphoria, analgesia, slower breathing, and constipation. Opium is the dried juice of the unripe seed capsule of the opium poppy. It may be the oldest drug on record, known to the Sumerians before BC.
Morphine and heroin Figure 6. When heroin was produced a few decades later, it was also initially thought to be a more potent, less addictive painkiller but was soon found to be much more addictive than morphine. Heroin is about twice as addictive as morphine, and creates severe tolerance, moderate physical dependence, and severe psychological dependence.
The danger of heroin is demonstrated in the fact that it has the lowest safety ratio 6 of all the drugs listed in Table 6. The opioids activate the sympathetic division of the ANS, causing blood pressure and heart rate to increase, often to dangerous levels that can lead to heart attack or stroke.
At the same time the drugs also influence the parasympathetic division, leading to constipation and other negative side effects. Symptoms of opioid withdrawal include diarrhea, insomnia, restlessness, irritability, and vomiting, all accompanied by a strong craving for the drug.
The powerful psychological dependence of the opioids and the severe effects of withdrawal make it very difficult for morphine and heroin abusers to quit using. In addition, because many users take these drugs intravenously and share contaminated needles, they run a very high risk of being infected with diseases. Opioid addicts suffer a high rate of infections such as HIV, pericarditis an infection of the membrane around the heart , and hepatitis B, any of which can be fatal.
The drugs that produce the most extreme alteration of consciousness are the hallucinogens , psychoactive drugs that alter sensation and perception and that may create hallucinations. The chemical compositions of the hallucinogens are similar to the neurotransmitters serotonin and epinephrine, and they act primarily as agonists by mimicking the action of serotonin at the synapses. The hallucinogens may produce striking changes in perception through one or more of the senses. In large part, the user tends to get out of the experience what he or she brings to it.
The hallucinations that may be experienced when taking these drugs are strikingly different from everyday experience and frequently are more similar to dreams than to everyday consciousness. Cannabis marijuana is the most widely used hallucinogen.
0コメント