The major cities of India are in the grip of the drug menace. This devastating vice finishes off the addicts by debilitating them physically and psychologically. A seminar on Drug Abuse held recently in Madras has painted a horrible picture of this malady. The most disturbing fact is that the university campuses, college premises and school grounds nourish this evil more and more.
Drug addiction implies physical dependence upon a drug including the development of tolerance and withdrawal. An addict who develops tolerance requires more of the drug to transport him to the world of fantasies. If the addict is not allowed to take the drug he suffers from painful and uncontrollable convulsions, vomiting, depression and various other maladies.
Many drugs give the user a kick eradicating frustrations and adversities that life throws in his way. What they forget or do not understand is that the problems drowned in drugs come back with a vengeance to torment them once the effect wears off. The addicts’ endeavour, is escapist and it is doomed to catastrophic failure even before it begins.
Drugs used by the addicts, particularly in India may be categorised into narcotics, hallucinogens, stimulants and sedatives. Marijuana, opium, heroin, barbiturates and amphatamines are all habit-forming drugs. Marijuana is the Indian hemp, its tetrahydro-cannabinol content is the real drug content and its largest concertration is in the flowering top of the plant. The resin collected from the tops of potent cannabis sativa is called hashish. It is considered to be five times stronger than marijuana. Side-effects of this drug are greater and more injurious. These drugs which are inhaled in smoke-rolled into cigarettes. But both marijuana and hashish can be added to food and drink. As soon as its smoke is inhaled eyes become red, heart beat increases and usually the smoker coughs. Hunger and drowsiness normally follow inhalations of smoke. The smoker gets distortions of visions and hearing. He loses all the sense of time though the smoker thinks that his thoughts have become clear and better. Hallucinations and delusions may also happen. Unfounded suspicion of anything accompanied by anxiety, uncontrolled laughter or weeping and irrational mental fixations also are noticed. Hallucinogens are drugs that provoke changes in sensation, thought process, self-awareness and emotion. Aberrations in the perceptions of time and space happen, illusion, delusion or hallucination may vary in intensity in accordance with the dosage inhaled. Marijuana smokers stand the danger of ceasing to become “high” on smoke and may have to take recourse to heavier drugs. And the results produced by the same amount of drug may vary in the same person depending upon circumstances.
LSD (Lysergic Acid) is the most powerful hallucinogen. Its intake dilates pupils of the eyes, flushes the face, raises body heat and heart beat. Blood pressure shoots up and the person feels chilly. Convulsions occur but rarely. As the effect of the drug wears off the symptoms disappear. Vision is most markedly affected, perception of the objects is distorted. The subject experiences transferred emotions; he may consider music just a picture. It can also fill the person with horror. Thus, extreme euphoria or insufferable terror is the result. Consequences are unpredictable-the extreme being homicide or suicide. The most detrimental effects of LSD is flashback. Such flashbacks can cause extreme anxiety.
Amphetamines called stimulants are supposed to increase alertness, increase vigour and reduce hunger. Medically it is used to reduce depression. Stimulants known as `appers’ or `pep pills’ are taken in capsules or tablets. They are also taken through inhalations or through injections. Some inject massive doses intravenously from one to a dozen times a day. This type of user is called a speed freak. In ordinary quantities it provides a temporary sense of alertness and well being. Hunger is reduced and the performance of an exhausted person improves. But intravenous intake in large quantities gives an ecstasy high for some time. Once it wears off, reinjection is needed. This goes on till the person breaks down physically followed by collapse and death. Social, familial and moral values erode.
Sedatives induce sleep and are capable of reducing tension taken in small doses. The largest group of sedatives is from barbiturates. Taken without medical supervision people may take over-doses and then become habituated. These drugs are called gold balls, sleepers and downers. Tranquilisers calm, relax and diminish anxiety. They may cause drowsiness also. A strong desire to take drugs develops. If a person takes a few barbiturate pills after drinking he may succumb to death. Barbiturates taken with narcotics, alcohol or tranquilisers can also prove fatal.
Narcotics relieve pain; opium and its active components such as morphine and heroin belong to this group. Morphine is bitter in taste. Opium has 10 percent morphine content. Dialetyl morphine hydrochloride is prepared by the action of an antibride on morphine. When mixed with sugar and other ingredients, this is called brown sugar. It is taken orally or by injecting intravenously. It is smoked in the Chinese way also. It accounts for about 90 percent of the drug intake. It has no medicine value.
People in all kinds of pain take heroin for relief. Pure heroin if injected can kill within minutes. Unclean implements used for injections may lead to viral hepatitis, skin abscess, inflammation of veins and congestion of the lungs. The addict may become prone to Tuberculosis.
Drug addiction reduces sober time available to a person. The personality of the addict is destroyed and his emotions become intense and distorted. Fertility is reduced and children born may have serious illness and withdrawal symptoms. The Indian government is making an all-out effort to check this diabolic trafficking of the drug.
Essay No. 2
Drug addiction is the worst social evil of modern civilization. It is spreading like cancer. The misguided and frustrated adults are the prey of this habit. Mostly of rich families, these people are becoming habitual of using drugs such as herion, smack, opium, charas, cocaine, ganja and brown sugar. Drug addiction is a part of western culture. It is thought is a thing of fashion and modernization. The worst aspect of this social evil is – if you start taking drug in fun or fashion, it becomes so habitual that it cannot be left easily. It is an invitation to death. This evil is reaching and spreading in Asian and African countries. Drug addiction is self- destruction. This may take sometimes as we see in case of cancer, but it is a sure stepping towards death.
Drugs have been used for medical purposes since ages. Never before this modern period. There was no misuse of drugs. Man is greedy by nature. To earn more in short period some anti social adulterated drugs cause deaths those who are busy in anti- human activity for their selfish motives, should be punished. There should be no encouragement from government department to anti- social elements. The public should also co- operation to make anti- social elements suffer.
Drug abuse is fast becoming very common among students. thousands of school and college going youngmen have become drug- addicts. This evil is more rampant in big cities. Villagers and the town people are still free form this abuse. Urban life is slowly becoming a mechanical life. it has become highly competitive and risky. Tension and cut-throat competition put an unbearable pressure on youngmen and women. Life becomes tiring and burdensome. Students tend to become escapists. As an escape from the drudgery of life, they take to drugs. In the beginning they turn to drugs just for fun and thrill. Then they get addicted to this abuse. They are compelled to even steal to buy drugs. They become physically and mentally wrecks. They invite their own doom.
Drug abuse has become a great social and cultural problem. It has been polluting the minds and morals of our youngmen. The menace of drugs can’t be tackled by the authorities alone. There should be a comprehensive and all- out – war to root out this evil from the students. rehabilitation centers should be opened to treat the addicts. However, the root of this evil lies in the disorder an degeneration of our social and family life. peaceful and purposeful social and family life will fill our youth with hope and faith in themselves. They will not be tempted or lured by the vicious addiction of drugs.
The abuse of drugs has now become an international problem. Recent studies show that 88% of heroin addicts in India are in the age group of 14-25 years. In fact at present drug abuse has become a craze among school and college students. drug habit is considered a fashion or a symbol of modernity at the beginning. But after some time it becomes a habit, making body weak and a prey of different diseases. Children having no sweet life, lack of healthy education , heavy burden of books; sex and violence seen through T.V. and cinema programmes; loss of moral values, uncertainty of future life prepare a youth to be a prey of this had habit. Drug affects a person physically, mentally, and spiritually leading to a wreck life. he lives only for these deadly drugs.
Drugs addiction must be fought on war footing. Concerning departments and public should be alert to remove this social evil. A great publicity should be made regarding this social evil. A large number of banners, posters and placards should be displayed. Evils of drug should be highlighted through the media- radio, television and press. The parents should be more careful about their wards specially in tender young age. The drug addicts should be kept under special care and treatment. Doubtful anti- social worker should be checked with regular attention and should be punished seriously if found guilty.
Essay No. 03
Drugs and Teenagers
The start of college is a new and different experience for all teenagers. They are keen to learn about their new surroundings and make new friends. At the same time, many teens consider drinking, smoking and drugs as cool. In a survey recently conducted on the abuse of alcohol, nicotine, and other harmful drugs, researchers studied that the maximum number of teenagers involved in smoking, drinking and drugs are in the age group of fourteen to twenty. In today’s society, the pressure to drink, smoke or use drugs to fit in has been seen in youth. On the basis of such surveys, it was found that these teenagers drink one to two times per week because they enjoy it. They feel that it is also a chance to have fun and hang out with their friends. However, teens say they do it out of boredom also.
Often, teens are anxious to find an alternative way to have fun and to escape from movies and television. For this reason, they jump at the chance together in a large group to socialize. They are willing to pay their pocket money for a cup of beer, i even if they know that drinking under age is illegal. Drinking alcohol comes with many responsibilities. These teens ‘responsible drinking’ as ‘having control of your action. In other words, teens drink as long as they know what they are doing. However, drinking teenagers are often found in situations where they act irresponsible. Teenagers are often caught driving while under the influence of alcohol. When teens get into the car, they do not think about the consequences. There is always that one thought in the back of everyone’s mind in this type of situation. They say, nothing bad is going to happen. Sadly, when something does happen, most of the time the drunk driver is never the one to be injured. It is always the innocent passengers or the victims on the road.
Smoking is another issue within the college community. Many teenagers who smoke have been doing so quite some time and started smoking at an early age. Even though most people do not agree with teens smoking, a good percentage of adults smoke cigarettes. Therefore, the influence to smoke is constantly around teens and young children. On the other hand, some teens also like to smoke socially. This usually occurs at parties or just when they feel like hanging around outside of their dorms. Drug usage is the third huge area of abuse among students in college. The majority of these teens have tried the most common gateway drug, marijuana. Many of these teenagers said they have also tried mushrooms, ecstasy, and speed. Peer pressure has nothing to do with their reasons for drinking, smoking, or doing drugs. They believe college is the time to live. Drinking alcohol, smoking cigarettes, and using drugs are not going to stop them from having the times of their lives. Only awareness can stop them.
About evirtualguru_ajaygourThe main objective of this website is to provide quality study material to all students (from 1st to 12th class of any board) irrespective of their background as our motto is “Education for Everyone”. It is also a very good platform for teachers who want to share their valuable knowledge.
"Addictive" redirects here. For other uses, see Addiction (disambiguation) and Addictive (disambiguation).
|Addiction and dependence glossary|
Addiction is a brain disorder characterized by compulsive engagement in rewarding stimuli despite adverse consequences. Despite the involvement of a number of psychosocial factors, a biological process – one which is induced by repeated exposure to an addictive stimulus – is the core pathology that drives the development and maintenance of an addiction. The two properties that characterize all addictive stimuli are that they are reinforcing (i.e., they increase the likelihood that a person will seek repeated exposure to them) and intrinsically rewarding (i.e., they are perceived as being inherently positive, desirable, and pleasurable).
Addiction is a disorder of the brain's reward system which arises through transcriptional and epigenetic mechanisms and occurs over time from chronically high levels of exposure to an addictive stimulus (e.g., eating food, the use of cocaine, engagement in sexual intercourse, participation in high-thrill cultural activities such as gambling, etc.).ΔFosB, a gene transcription factor, is a critical component and common factor in the development of virtually all forms of behavioral and drug addictions. Two decades of research into ΔFosB's role in addiction have demonstrated that addiction arises, and the associated compulsive behavior intensifies or attenuates, along with the overexpression of ΔFosB in the D1-typemedium spiny neurons of the nucleus accumbens. Due to the causal relationship between ΔFosB expression and addictions, it is used preclinically as an addiction biomarker. ΔFosB expression in these neurons directly and positively regulates drug self-administration and reward sensitization through positive reinforcement, while decreasing sensitivity to aversion.[note 1]
As described by two groups of researchers, addiction exacts an "astoundingly high financial and human toll" on individuals and society as a whole through the direct adverse effects of drugs, associated healthcare costs, long-term complications (e.g., lung cancer with smoking tobacco, liver cirrhosis with drinking alcohol, or meth mouth from intravenous methamphetamine), the functional consequences of altered neural plasticity in the brain, and the consequent loss of productivity. Classic hallmarks of addiction include impaired control over substances or behavior, preoccupation with substance or behavior, and continued use despite consequences. Habits and patterns associated with addiction are typically characterized by immediate gratification (short-term reward), coupled with delayed deleterious effects (long-term costs).
Examples of drug and behavioral addictions include: alcoholism, amphetamine addiction, cocaine addiction, nicotine addiction, opiate addiction, food addiction, gambling addiction, and sexual addiction. The only behavioral addiction recognized by the DSM-5 and the ICD-10 is gambling addiction. The term addiction is misused frequently to refer to other compulsive behaviors or disorders, particularly dependence, in news media. An important distinction between drug addiction and dependence is that drug dependence is a disorder in which cessation of drug use results in an unpleasant state of withdrawal, which can lead to further drug use. Addiction is the compulsive use of a substance or performance of a behavior that is independent of withdrawal.
This section needs expansion. You can help by adding to it.(February 2016)
Cognitive control and stimulus control, which is associated with operant and classical conditioning, represent opposite processes (i.e., internal vs external or environmental, respectively) that compete over the control of an individual's elicited behaviors. Cognitive control, and particularly inhibitory control over behavior, is impaired in both addiction and attention deficit hyperactivity disorder. Stimulus-driven behavioral responses (i.e., stimulus control) that are associated with a particular rewarding stimulus tend to dominate one's behavior in an addiction.
Stimulus control of behavior
See also: Stimulus control
Cognitive control of behavior
See also: Cognitive control
Main article: Behavioral addiction
The term behavioral addiction correctly refers to a compulsion to engage in a natural reward – which is a behavior that is inherently rewarding (i.e., desirable or appealing) – despite adverse consequences. Preclinical evidence has demonstrated that marked increases in the expression of ΔFosB through repetitive and excessive exposure to a natural reward induces the same behavioral effects and neuroplasticity as occurs in a drug addiction.
Reviews of both clinical research in humans and preclinical studies involving ΔFosB have identified compulsive sexual activity – specifically, any form of sexual intercourse – as an addiction (i.e., sexual addiction). Moreover, reward cross-sensitization between amphetamine and sexual activity, meaning that exposure to one increases the desire for both, has been shown to occur preclinically and clinically as a dopamine dysregulation syndrome; ΔFosB expression is required for this cross-sensitization effect, which intensifies with the level of ΔFosB expression.
Reviews of preclinical studies indicate that long-term frequent and excessive consumption of high fat or sugar foods can produce an addiction (food addiction).
Gambling is a natural reward which is associated with compulsive behavior and for which clinical diagnostic manuals, namely the DSM-5, have identified diagnostic criteria for an "addiction". There is evidence from functional neuroimaging that gambling activates the reward system and the mesolimbic pathway in particular. Similarly, shopping and playing videogames are associated with compulsive behaviors in humans and have also been shown to activate the mesolimbic pathway and other parts of the reward system. Based upon this evidence, gambling addiction, video game addiction and shopping addiction are classified accordingly.
There are a range of genetic and environmental risk factors for developing an addiction that vary across the population. Roughly half of an individual's risk for developing an addiction is derived from genetics, while the other half is derived from the environment. However, even in individuals with a relatively low genetic loading, exposure to sufficiently high doses of an addictive drug for a long period of time (e.g., weeks–months) can result in an addiction. In other words, anyone can become an addict under the right circumstances.
It has long been established that genetic factors along with environmental (e.g., psychosocial) factors are significant contributors to addiction vulnerability. Epidemiological studies estimate that genetic factors account for 40–60% of the risk factors for alcoholism. Similar rates of heritability for other types of drug addiction have been indicated by other studies. Knestler hypothesized in 1964 that a gene or group of genes might contribute to predisposition to addiction in several ways. For example, altered levels of a normal protein due to environmental factors could then change the structure or functioning of specific brain neurons during development. These altered brain neurons could change the susceptibility of an individual to an initial drug use experience. In support of this hypothesis, animal studies have shown that environmental factors such as stress can affect an animal's genotype.
Overall, the data implicating specific genes in the development of drug addiction is mixed for most genes. One reason for this may be that the case is due to a focus of current research on common variants. Many addiction studies focus on common variants with an allele frequency of greater than 5% in the general population, however when associated with disease, these only confer a small amount of additional risk with an odds ratio of 1.1–1.3 percent. On the other hand, the rare variant hypothesis states that genes with low frequencies in the population (<1%) confer much greater additional risk in the development of disease.
Genome-wide association studies (GWAS) are a recently developed research method which are used to examine genetic associations with dependence, addiction, and drug use. These studies employ an unbiased approach to finding genetic associations with specific phenotypes and give equal weight to all regions of DNA, including those with no ostensible relationship to drug metabolism or response. These studies rarely identify genes from proteins previously described via animal knockout models and candidate gene analysis. Instead, large percentages of genes involved in processes such as cell adhesion are commonly identified. This is not to say that previous findings, or the GWAS findings, are erroneous. The important effects of endophenotypes are typically not capable of being captured by these methods. Furthermore, genes identified in GWAS for drug addiction may be involved either in adjusting brain behavior prior to drug experiences, subsequent to them, or both. 
A study that highlights the significant role genetics play in addiction is the twin studies. Twins have similar and sometimes identical genetics. Analyzing these genes in relation to genetics has helped geneticists understand how much of a role genes play in addiction. Studies performed on twins found that rarely did only one twin have an addiction. In most cases where at least one twin suffered from an addiction, both did, and often to the same substance.
Environmental risk factors for addiction are the experiences of an individual during their lifetime that interact with the individual's genetic composition to increase or decrease the his or her vulnerability to addiction. A number of different environmental factors have been implicated as risk factors for addiction, including various psychosocial stressors; however, an individual's exposure to an addictive drug is by far the most significant environmental risk factor for addiction. The National Institute on Drug Abuse cites lack of parental supervision, the prevalence of peer substance use, drug availability, and poverty as risk factors for substance use among children and adolescents.
Adverse childhood experiences (ACEs) are various forms of maltreatment and household dysfunction experienced in childhood. The Adverse Childhood Experiences Study by the Centers for Disease Control and Prevention has shown a strong dose–response relationship between ACEs and numerous health, social, and behavioral problems throughout a person's lifespan, including those associated with substance abuse. Children's neurological development can be permanently disrupted when they are chronically exposed to stressful events such as physical, emotional, or sexual abuse, physical or emotional neglect, witnessing violence in the household, or a parent being incarcerated or suffering from a mental illness. As a result, the child's cognitive functioning or ability to cope with negative or disruptive emotions may be impaired. Over time, the child may adopt substance use as a coping mechanism, particularly during adolescence. A study of 900 court cases involving children who experienced abuse found that a vast amount of them went on to suffer from some form of addiction in their adolescence or adult life. This pathway towards addiction that is opened through stressful experiences during childhood can be avoided by a change in environmental factors throughout an individuals life and opportunities of professional help.
Adolescence represents a period of unique vulnerability for developing addiction. In adolescence, the incentive–rewards systems in the brain mature well before the cognitive control center. This consequentially grants the incentive–rewards systems a disproportionate amount of power in the behavioral decision making process. Therefore, adolescents are increasingly likely to act on their impulses and engage in risky, potentially addicting behavior before considering the consequences. Not only are adolescents more likely to initiate and maintain drug use, but once addicted they are more resistant to treatment and more liable to relapse. Statistics have shown that those who start to drink alcohol at a younger age are more likely to become dependent later on. About 33% of the population tasted their first alcohol between the ages of 15 and 17, while 18% experienced it prior to this. As for alcohol abuse or dependence, the numbers start off high with those who first drank before they were 12 and then drop off after that. For example, 16% of alcoholics began drinking prior to turning 12 years old, while only 9% first touched alcohol between 15 and 17. This percentage is even lower, at 2.6%, for those who first started the habit after they were 21.
Most individuals are exposed to and use addictive drugs for the first time during their teenage years. In the United States, there were just over 2.8 million new users of illicit drugs in 2013, or about 7,800 new users per day. Over half (54.1 percent) were under 18 years of age.
Individuals with comorbid (i.e., co-occurring) mental health disorders such as depression, anxiety, attention-deficit/hyperactivity disorder (ADHD) or post-traumatic stress disorder are more likely to develop substance use disorders. The National Institute on Drug Abuse cites early aggressive behavior as a risk factor for substance use.
Transgenerational epigenetic factors
See also: Transgenerational epigenetic inheritance
Epigenetic genes and their products (e.g., proteins) are the key components through which environmental influences can affect the genes of an individual; they also serve as the mechanism responsible for the transgenerational epigenetic inheritance of behavioral phenotypes, a phenomenon in which environmental influences on the genes of a parent can affect the associated traits and behavioral phenotypes of their offspring (e.g., behavioral responses to certain environmental stimuli). In addiction, epigenetic mechanisms play a central role in the pathophysiology of the disease; it has been noted that some of the alterations to the epigenome which arise through chronic exposure to addictive stimuli during an addiction can be transmitted across generations, in turn affecting the behavior of one's children (e.g., the child's behavioral responses to addictive drugs and natural rewards). More research is needed to determine the specific epigenetic mechanisms and the nature of heritable behavioral phenotypes that arise from addictions in humans. Based upon preclinical evidence with lab animals, the addiction-related behavioral phenotypes that are transmitted across generations may serve to increase or decrease the child's risk of developing an addiction.
|Transcription factor glossary|
Signaling cascade in the nucleus accumbens that results in psychostimulant addiction
This diagram depicts the signaling events in the brain's reward center that are induced by chronic high-dose exposure to psychostimulants that increase the concentration of synaptic dopamine, like amphetamine, methamphetamine, and phenethylamine. Following presynaptic dopamine and glutamateco-release by such psychostimulants,postsynaptic receptors for these neurotransmitters trigger internal signaling events through a cAMP-dependent pathway and a calcium-dependent pathway that ultimately result in increased CREB phosphorylation. Phosphorylated CREB increases levels of ΔFosB, which in turn represses the c-Fos gene with the help of corepressors;c-Fosrepression acts as a molecular switch that enables the accumulation of ΔFosB in the neuron. A highly stable (phosphorylated) form of ΔFosB, one that persists in neurons for 1–2 months, slowly accumulates following repeated high-dose exposure to stimulants through this process. ΔFosB functions as "one of the master control proteins" that produces addiction-related structural changes in the brain, and upon sufficient accumulation, with the help of its downstream targets (e.g., nuclear factor kappa B), it induces an addictive state.
Chronic addictive drug use causes alterations in gene expression in the mesocorticolimbic projection. The most important transcription factors that produce these alterations are ΔFosB, cAMP response element binding protein (CREB), and nuclear factor kappa B (NF-κB). ΔFosB is the most significant biomolecular mechanism in addiction because the overexpression of ΔFosB in the D1-typemedium spiny neurons in the nucleus accumbens is necessary and sufficient for many of the neural adaptations and behavioral effects (e.g., expression-dependent increases in drug self-administration and reward sensitization) seen in drug addiction. ΔFosB expression in nucleus accumbensD1-typemedium spiny neurons directly and positively regulates drug self-administration and reward sensitization through positive reinforcement while decreasing sensitivity to aversion.[note 1] Specific drug addictions in which ΔFosB has been implicated in addictions to alcohol, amphetamine, cannabinoids, cocaine, methylphenidate, nicotine, phenylcyclidine, propofol, opiates, and substituted amphetamines, among others.ΔJunD, a transcription factor, and G9a, a histone methyltransferase, both oppose the function of ΔFosB and inhibit increases in its expression. Increases in nucleus accumbens ΔJunD expression (via viral vector-mediated gene transfer) or G9a expression (via pharmacological means) reduces, or with a large increase can even block, many of the neural and behavioral alterations seen in chronic drug abuse (i.e., the alterations mediated by ΔFosB).
ΔFosB also plays an important role in regulating behavioral responses to natural rewards, such as palatable food, sex, and exercise. Natural rewards, like drugs of abuse, induce gene expression of ΔFosB in the nucleus accumbens, and chronic acquisition of these rewards can result in a similar pathological addictive state through ΔFosB overexpression. Consequently, ΔFosB is the key transcription factor involved in addictions to natural rewards (i.e., behavioral addictions) as well; in particular, ΔFosB in the nucleus accumbens is critical for the reinforcing effects of sexual reward. Research on the interaction between natural and drug rewards suggests that dopaminergic psychostimulants (e.g., amphetamine) and sexual behavior act on similar biomolecular mechanisms to induce ΔFosB in the nucleus accumbens and possess bidirectional cross-sensitization effects that are mediated through ΔFosB. This phenomenon is notable since, in humans, a dopamine dysregulation syndrome, characterized by drug-induced compulsive engagement in natural rewards (specifically, sexual activity, shopping, and gambling), has also been observed in some individuals taking dopaminergic medications.
ΔFosB inhibitors (drugs or treatments that oppose its action) may be an effective treatment for addiction and addictive disorders.
The release of dopamine in the nucleus accumbens plays a role in the reinforcing qualities of many forms of stimuli, including naturally reinforcing stimuli like palatable food and sex. Altered dopamine neurotransmission is frequently observed following the development of an addictive state. In humans and lab animals that have developed an addiction, alterations in dopamine or opioid neurotransmission in the nucleus accumbens and other parts of the striatum are evident. Studies have found that use of certain drugs (e.g., cocaine) affect cholinergic neurons that innervate the reward system, in turn affecting dopamine signaling in this region.
Summary of addiction-related plasticity
Main article: Reward system
This section needs expansion. You can help by adding to it.(August 2015)
Understanding the pathways in which drugs act and how drugs can alter those pathways is key when examining the biological basis of drug addiction. The reward pathway, known as the mesolimbic pathway, or its extension, the mesocorticolimbic pathway, is characterized by the interaction of several areas of the brain.
- The projections from the ventral tegmental area (VTA) are a network of dopaminergicneurons with co-localized postsynaptic glutamate receptors (AMPAR and NMDAR). These cells respond when stimuli indicative of a reward are present. The VTA supports learning and sensitization development and releases DA into the forebrain. These neurons also project and release DA into the nucleus accumbens, through the mesolimbic pathway. Virtually all drugs causing drug addiction increase the dopamine release in the mesolimbic pathway, in addition to their specific effects.
- The nucleus accumbens (NAcc) is one output of the VTA projections. The nucleus accumbens itself consists mainly of GABAergicmedium spiny neurons (MSNs). The NAcc is associated with acquiring and eliciting conditioned behaviors, and is involved in the increased sensitivity to drugs as addiction progresses. Overexpression of ΔFosB in the nucleus accumbens is a necessary common factor in essentially all known forms of addiction; ΔFosB is a strong positive modulator of positively reinforced behaviors.
- The prefrontal cortex, including the anterior cingulate and orbitofrontal cortices, is another VTA output in the mesocorticolimbic pathway; it is important for the integration of information which helps determine whether a behavior will be elicited. It is also critical for forming associations between the rewarding experience of drug use and cues in the environment. Importantly, these cues are strong mediators of drug-seeking behavior and can trigger relapse even after months or years of abstinence.
Other brain structures that are involved in addiction include:
- The basolateral amygdala projects into the NAcc and is thought to also be important for motivation.
- The hippocampus is involved in drug addiction, because of its role in learning and memory. Much of this evidence stems from investigations showing that manipulating cells in the hippocampus alters dopamine levels in NAcc and firing rates of VTA dopaminergic cells.
Role of dopamine and glutamate
Dopamine is the primary neurotransmitter of the reward system in the brain. It plays a role in regulating movement, emotion, cognition, motivation, and feelings of pleasure. Natural rewards, like eating, as well as recreational drug use cause a release of dopamine, and are associated with the reinforcing nature of these stimuli. Nearly all addictive drugs, directly or indirectly, act upon the brain's reward system by heightening dopaminergic activity.
Excessive intake of many types of addictive drugs results in repeated release of high amounts of dopamine, which in turn affects the reward pathway directly through heightened dopamine receptor activation. Prolonged and abnormally high levels of dopamine in the synaptic cleft can induce receptor downregulation in the neural pathway. Downregulation of mesolimbic dopamine receptors can result in a decrease in the sensitivity to natural reinforcers.
Drug seeking behavior is induced by glutamatergic projections from the prefrontal cortex to the nucleus accumbens. This idea is supported with data from experiments showing that drug seeking behavior can be prevented following the inhibition of AMPA glutamate receptors and glutamate release in the nucleus accumbens.
|Neural effects||Behavioral effects|
|c-Fos||↓||Molecular switch enabling the chronic|
induction of ΔFosB[note 2]