Drugs Addiction and the Brain's Reward Circuits

Psychoactive drugs and Drug administration

Basic principles of Drug action

Psychoactive drugs

Drugs that influence subjective experience and behavior by acting on the nervous system

Drug administration

Route of administration influences the rate at which and the degree to which the drug teaches its site of action

Ingestion

Easy and relatively safe

Absorption via digestive tract is unpredictable

Injection

Bypasses digestive tract

Subcutaneously, Intramuscularly, and Intravenously

Type of injection

Subcutaneously

Under the skin

Intramuscularly

Into large muscles

Intravenously

Into veins, drug delivered directly to brain

Inhalation

Absorbed through capillaries in lungs

Common used in tobacco and Marijuana

Difficult to precisely regulate the dose of inhaled drugs

Absorption

Through mucous membranes

Drug metabolism

Action of most drugs terminated by enzymes in the liver

Drug tolerance

Decreased sensitivity to a drug as a consequence of exposure to it

• Has lesser effect or it takes more drug to produce the same effect

Cross tolerance

Exposure to one drug can produce tolerance to similar drugs

Cross tolerance

Exposure to one drug can produce tolerance to similar drugs

Drug sensitization

Increasing sensitivity to a drug or “inverse tolerance”

Metabolic

Less drug is getting to the action

Functional

Decreased responsiveness at the site of action,fewer receptors, decreased efficiency of binding at receptors, receptors less responsive

Withdrawal syndrome

Adverse physiological reaction after sudden elimination of the drug

Physical dependence

Withdrawal symptoms in the absence of the drug

Tolerance to its effects with repeated use

Psychological dependence

“a relatively extreme, pathological state in which obtaining, taking, and

recovering from a drug represents a loss of behavioral control over drug

taking which occurs at the expense of most other activities and despite

adverse consequences” (Altman et al)

Drug use

Taking a psychoactive substance for non-medical purposes, out of curiosity

Drug abuse

Drug use that leads to problems

Drug dependence

A maladaptive pattern of drug use leading to clinically-significant impairment or distress, associated with difficulty in controlling drug-taking behavior, withdrawal, and tolerance

Addicts

Those who continue to use a drug despite its adverse effects on health and social life

Contingent drug tolerance

Tolerance only develop tio drug effects that are experienced

Condition drug tolerance

Maximal tolerance effects are seen in the environment in which a drug is usually taken

Conditioned withdrawal effects

Withdrawal elicited by drug-related cues

Conditioned compensatory response theory

Conditional stimuli that predict drug administration come to elicit conditional responses opposite to the unconditional effects of the drug

Tobacco, Alcohol, Marijuana, Cocaine, and Opiates

Five commonly abused drugs

Nicotine

A kind of tobacco that have a major psychoactive ingredient

Smoker’s syndrome

Chest pain, labored breathing, wheezing, coughing, increased susceptibility to respiratory infections

Buerger’s disease

Blood vessels become constricited

Alcohol

A depressant; because at moderate to high it depresses neural firing while low can stimulate neural firing and facilitate social interactions

Cannabis sativa

A kind of marijuana that is a common hemp plant

Sativa

A kind of marijuana that is uplifting and enegetic

Cerebral, pacey, or hallucinogenic

Best suited for day use

Indica

A kind of marijuana that is relaxing and calming

Boddy buzz or ‘couch lock’

Best suited for night use

Cocaine

Its derivatives —- commonly abused

Crack

A potent, cheap, and smokable form of cocaine

Amphetamine

Effects like cocaine - can produce psychosis

MDMA (ecstasy)

Impairs dopaminergic and serotonergic function in animal studies; human relevance unclear

Opiates

Obtained from the opium poppy

Methadone

Binds to opiate receptors

Buprenorphine

Similar to methadone but longer lasting

Physical-dependence theory

Dependence due to pain of withdrawal

Positive-incentive theories

Expected pleasure producing

Incentive-sensitization theory

Positive-incentive value of addictive drugs increase

Relapse

Return to one’s drug taking habit after a period of voluntary abstinence

Stress, Priming, and Environmental cues

3 Fundamentally difference causes

Nigrostriatal Pathway

Substantia nigra neurons projecting to dorsal striatum

Mesocorticolimbic pathways

Ventral tegmental area neurons projecting to cortical and limbic sites, including the nucleus accumbens

Drug self-administration parafigm

Drug self-administration through cannulas (thin tubes) to the blood stream

Conditioned place-preference

Lab animals choose to spend more time in cage compartment where drugs were administered than elsewhere

Inital drug taking

Involvement of mesocorticolimbic pathway (nucleus accumbens), prefrontal lobes, and amygdala

Craving and compulsive drug use

Dorsal striatum and hypothalamic stress circuits take over

Relapse

Priming doses (prefrontal cortex), drug-associated cues (amygdala), and stress (hypothalamic stress circuits)