Lecture 13: Addiction Flashcards
Basic Principles of Drug Addiction:
Drug Administration and Absorption
(4 ways)
1 of 4 ways; by oral ingestion, by injection, by inhalation or by absorption via the mucus membrane in either the nose, mouth, eye or rectum.
The route of administration influences the rate and degree to which the drug reaches its site of action in the body
Basic Principles of Drug Addiction:
Drug Administration and Absorption
- Oral injestion
Drug dissolves in fluids of stomach, carried to intestine, absorbed into bloodstream
Drugs that cannot be readily absorbed from the digestive tract or that are broken down into inactive metabolites before they can be absorbed must be ingested some other way
Some drugs, like alcohol, pass readily through stomach walls
Adv/ Easy and relatively safe
Disadv/ Unpredictability: Influenced by amount of food and type in stomach
Basic Principles of Drug Addiction:
Drug Administration and Absorption
- Injection
Strong, fast, predictable effects
- Subcutaneously (SC) into fatty tissue beneath skin
- Intramuscularly (IM) into large muscles
- Intravenously (IV) directly into veins
–> Bloodstream = directly to brain
Basic Principles of Drug Addiction:
Drug Administration and Absorption
- Inhalation
Absorbed through rich networks of capillaries in lungs e.g. anaesthetics (gas + air), marijuana, tobacco
Difficult to regulate dosage precisely
Basic Principles of Drug Addiction:
Drug Administration and Absorption
- Mucus membranes
Nose, mouth, rectum
Cocaine snorted through nasal membranes, damages them
Drug Penetration of CNS
When a drug enters bloodstream, the blood brain barrier makes it difficult for dangerous blood-born chemicals to pass from blood vessels of CNS into its neurons
Mechanisms of Drug Action:
Psychoactive drugs influence the nervous system - some act diffusely on neural membranes throughout CNS e.g. alcohol and some general anaesthetics
Others act in specific way: Bind to particular synaptic receptor to influence… - synthesis - transport - release - deactivation … of particular neurotransmitters
OR by influencing the chain of chemical reactions elicited in post-synaptic neurons by activation of their receptors
Drug Metabolism and Elimination:
Action of most drugs is terminated by enzymes synthesised by the liver - enzymes stimulate conversion of active drugs into non-active forms –> Drug Metabolism - Eliminates drugs ability to pass through lipid membranes of cells, can’t penetrate blood brain barrier
Small amounts of psychoactive drugs are passed from the body in urine, sweat, faeces, breath and mother’s milk
Drug Tolerance:
Definition of drug tolerance
Drug tolerance is a state of decreased sensitivity to a drug that develops as a result of increased exposure
Drug Tolerance:
Demonstrated in 2 ways
- Showing the same amount of drug has less effect than before
- Showing it takes more of the drug to produce the same effect
This phenomena can be represented by Dose Response Curves (graph of magnitude of effect of different drug doses) – tolerance is shown by a shift to the right
Drug Tolerance:
3 important points about drug tolerance?
- Cross tolerance: One drug can produce tolerance to other drugs with similar mechanisms
- Drug tolerance often develops to some effects of a drug but not others
Drug Sensitisation: Increasing sensitivity to a drug
- Not a unitary phenomenon - no single mechanism underlies all drug tolerance, there are 2 main categories of tolerance
Drug Tolerance:
Types of tolerance
(2 types)
Metabolic Tolerance: Drug tolerance that results from changes that reduce the amount of the drug getting to the sites of action
Functional Tolerance: Tolerance that results from changes that reduce reactivity of the sites of action to the drug
- Tolerance to psychoactive drugs is largely functional, can result from several types of adaptive neural change e.g. exposure to drug can reduce number of receptors for it, decrease efficiency for which it binds to receptors or diminish the impact of receptor binding on activity of the cell
- -> Neural changes can be caused by epigenetic mechanisms that affect gene expression
Drug withdrawal Effects and Physical Dependence
Sudden elimination of a drug from the body can trigger adverse physiological reaction (withdrawal syndrome), evidence of physiological dependency
The effects of drug withdrawal are basically opposite to effect of drug e.g. effect of withdrawal from anticonvulsant drugs can trigger convulsions
Withdrawal effects are produced by same neural changes that produce tolerance –> Exposure produces compensatory changes in nervous system, offset drugs effect and produce tolerance, so when the drug is eliminated, compensatory neural changes, without drug to offset, them manifest themselves as withdrawals (opposite to initial effects of the drug)
Severity depends on drug, duration & degree of drug exposure and speed of elimination
What is addiction?
Addict: Habitual drug user who continues to use drugs despite adverse effects on their health, social life, and despite their repeated efforts to stop
NOT the same as physical dependence, though this is often not motivating factor in addition
Food, gambling, sex additions may be based on similar mechanisms
Role of Learning in Drug Tolerance:
Two types of learned drug tolerance
- Contingent drug tolerance
2. Conditioned drug tolerance
Role of Learning in Drug Tolerance:
- Contingent drug tolerance
Demonstrations that tolerance develops only to drug effects that are actually experienced
Employs before and after design
e.g. painkiller and knee example
- take pk and get kicked in the knee
- knee doesn’t hurt because of pk
- repeat every day for a month
- tolerance to pk develops, stops working
- haven’t actually developed tolerance to pk just it’s effects on knee kicks
we know this because…
- different hypothetical scenario
- kick knee and give pk AFTER
- repeat for month
- knee hurts obviously
THEN - give painkiller BEFORE knee
- knee doesnt hurt, no tolerance to drug
Tolerance is contingent on experiencing the effects of it on knee bashing specifically
Role of Learning in Drug Tolerance:
- Conditioned drug tolerance
Demonstrations that tolerance effects are maximally expressed only when a drug is administered in the same situation it was previously administered –> Focuses on situations where drugs are taken
Addicts particularly susceptible to lethal effects of an overdose when drug administered in new context e.g. a new house, toilet cubicle etc
**Serious problem for health – we can have difficulty predicting direction of conditioned effects
Role of Learning in Drug Tolerance:
- Conditioned drug tolerance
Siegel’s Conditioned Compensatory Response Theory
Siegel’s Conditioned Compensatory Response Theory –
Sees each incidence of drug administration as a pavlovian conditioning trial, in which, various environmental stimuli regularly present when drug is administered act as predictors of drug administration.
Suggests conditioned environmental predictors come to elicit compensatory responses that are opposite to the action of the drug, to offset it’s effects. These compensatory responses become greater and greater with increasing incidence – producing situationally specific tolerance.
–> Ramsay and Wood argue unconditioned stimulus is disruption of neural functioning directly produced by drug, unconditional responses are various neutrally mediated compensatory reactions to unconditional stimulus
Types of stimuli:
- Exteroceptive stimuli - external stimuli like environment
- Interoceptive stimuli - internal stimuli like initial feelings produced by the drug ritual
Five Commonly Abused Drugs:
List
- Tobacco
- Alcohol
- Marijuana
- Cocaine and other stimulants
- Opiates: Heroin and Morphine
Five Commonly Abused Drugs:
- Tobacco
Overview
- Nicotine is the main psychoactive ingredient in cigarettes
- absorbed through lungs along with 4,000 other chemicals - ‘tar’.
- Non-smokers - nausea, vomiting, coughing, sweating, abdominal cramps, dizziness, flushing
- Smokers - relaxed, alert, less hungry
- withdrawal effects include depression, anxiety, restlessness, irritability, constipation, difficulty sleeping, difficulty concentrating
- 65% heritability for nicotine addiction (twin studies), 70% of people who experiment with smoking become addicted and only 20% of quitting attempts are successful after 2 years
Five Commonly Abused Drugs:
- Tobacco
Smokers Syndrome
Chest pain, laboured breathing, wheezing, coughing, heightened susceptibility to infections of respiratory tract
Smoking increases risk of cancer of larynx (voice box), mouth and heart, oesophagus, kidneys, bladder, pancreas, stomach
Relaxing effect of smoking reflects temporary reversal of stress caused by smoker’s addiction, stress is increased between cigarettes – smokers are more prone to panic attacks
Five Commonly Abused Drugs:
- Tobacco
Buerger’s Disease
Study - 15/100,000 people (mainly male smokers)
Characterised by blood vessels becoming constricted, especially those supplying legs
- Patient with condition continues to smoke, gangrene sets in, amputations occur, need to stop smoking for gangrene to clear up, people carry on even following 2-3rd amputation
Five Commonly Abused Drugs:
- Tobacco
Smoking doesn’t just affect smokers
Someone lives/works with smokers, more likely to develop heart disease and cancer
Nicotine is a teratogen (agent that can disturb normal development of foetus) - increases likelihood of miscarriage, stillbirth, early death of child
- Nicotine levels in blood of breastfed infants as great as those in blood of smoking others