Exam Three Biopsychology Drug Addiction and the Brain s Reward Circuits Chemicals that harm with pleasure Basic Principles of Drug Action o DSM criteria three or more of the following Tolerance Withdrawal Persistent desire unsuccessful attempts to cut down or control use Used in larger amount or for a longer time than intended Great deal of time spent to obtain use or recover Continued use despite physical or psychological problems Important social occupational or recreational activities given up reduced because of drug use o What is addiction Addiction Persistent use of a drug despite its destructive effects on health and social life Most often starts in adolescence or young adulthood About 50 of cases of addiction begin between 15 18 and very few begin after 20 o Psychoactive drug influence subjective experience and behavior by acting on the nervous system o Drug administration route of administration influences rate and degree to which a drug reaches its site of action Four main routes Ingestion oral route Preferred route for most convenient Absorption via digestive tract effects are unpredictable o Depends on food in digestive tract and enzyme breakdown Injection bypasses digestive tract Subcutaneous SC under skin Intramuscular IM into large muscles Intravenous IV into veins drug delivered directly to brain Favored route in medical practice strong fast and predictable Favored route by addicts esp heroin dangerous because of risk of death from overdose impure drugs or allergic reaction Inhalation tobacco marijuana Absorbed into bloodstream through capillaries in lungs Dosage is hard to regulate and have serious lung damage risk Mucous Membranes Nose mouth rectum Problematic membranes can be easily damaged Mechanisms of Drug Tolerance o Must get to brain and pass through blood brain barrier difficult to do o Drug metabolism Action of most drugs terminated by enzymes in liver o Small amount can be excreted in urine sweat feces breath and mother s milk o When drug has penetrated CNS can influence neural activity in many ways Act diffusely on neural membranes Increase decrease resting membrane potential on neurons Interact specifically with particular classes of neurotransmitters and receptors Bind with receptors on post pre synaptic membranes to influence function of a given neuron o Drug Tolerance Decreased sensitivity to a drug as a consequence of exposure to it How to measure it Measuring the decrease in the response elicited by the same dose of the drug Measuring the increase in the amount of drug required to produce the same effect Tolerance shifts the dose response curve to the RIGHT Cross tolerance Exposure to one drug can produce tolerance to similar drugs Example alcohol and benzodiazepines Tolerance often develops to SOME effects and NOT others Example nauseating effects of alcohol tobacco vs psychoactive effects More than one form of tolerance Metabolic o Less drug is getting to the site of action Functional underlies most drug tolerance o Decreased responsiveness at site of action Like fewer receptors decreased efficiency of binding receptors are less o Withdrawal Effects responsive Withdrawal Decreased sensitivity to a drug that comes from continued use seen when drug use is terminated AND when someone is physically dependent The user must take larger and larger amounts of drug for it to be effective Symptoms opposite to drug s effects Ex Withdrawal of anti consultants produces convulsions Ex Withdrawal of sleeping pills produces insomnia Shows that withdrawal effects are probably the result of the SAME mechanisms underlying tolerance tolerance o Body has made changes to compensate or oppose drug s presence producing o Without the drug present all you get is compensating counterbalancing effects Effect of heroin Euphoria constipation relaxation lead to withdrawal effects of dysphoria cramping Effects are manifestations of counteracting opponent mechanisms that body has and diarrhea and agitation established to tolerate heroin Relation between drug tolerance and withdrawal effects Same neurophysiological changes that develop in response to drug exposure and produce drug tolerance As changes develop tolerance increases and as they subside severity of withdrawal decreases Shows that tolerance and withdrawal are part of same process o Conditioning learning plays MAJOR role in manifestations of tolerance withdrawal Contingent drug tolerance Tolerance only develops to drug effects that are experienced Conditioned drug tolerance Maximal tolerance is seen in environment in which a drug is usually taken Contingent Tolerance Conditioned drug tolerance If drug tolerance becomes situationally specific drug addicts become more likely to overdose is unfamiliar surrounding Conditioned withdrawal effects Withdrawal elicited by drug related cues stimuli repeatedly paired with drug o Final points Addiction does NOT equal physical dependence Avoidance of withdrawal is rarely primary motivating force behind addictive behaviors Addicts often renew addictive behaviors after years of abstinence when simple physical withdrawal symptoms are unlikely to be severe Five Commonly Abused Drugs o All psychoactive affect dopamine release and influence activity in nucleus accumbens o Tobacco Facts Major psychoactive ingredient is nicotine About 70 of those who experiment with smoking become addicted o Vs 30 for heroin Only about 20 of attempts to stop are successful Long term effects Smoker s syndrome chest pain labored breathing wheezing coughing increased susceptibility to upper respiratory infections Susceptible to lung disorders pneumonia bronchitis emphysema lung cancer o Quitting smoking by age 40 adds about 9 years to life before age 30 is best WHO world health organization estimates 50 people who start at adolescence and continue smoking throughout life will die from smoking related disease In about 3 years largest single health problem worldwide The leading cause of preventable death in developed countries Other animals willing to self administer nicotine o Nicotine stimulates nicotinic acetylcholine receptors o Increases activity of dopaminergic neurons of mesolimbic system VTA to nucleus accumbens and cortical sites AND causes dopamine to be released in nucleus accumbens o Alcohol Facts About 10 of those who experiment with become addicted Depressant Heritability is about 55 Metabolic and functional tolerance develops Affects almost every tissue in the body Two primary sites of action