Lecture 16: Substance Misuse Flashcards
Define dependance and addiction
Dependance: physical need the body develops towards a partciular substance
Addiction: The altered behavious as a reuslt of an over whleming pshchological need for a substance.
Define substance misuse and What are the associated components of substance misuse?
Substance misuse is a behvioural pattern of drug use, characterised by; an overhwleming involbvement with the use of a drug, the securing of its supply, a high tendency to relapse after withdrawal
- Behavioural aspects
- Physical aspects
- Psychological and associative aspects
- Socioeconomic/ Environmental aspects
What are the stages of addiction?
- Binge and intoxication
- Withdrawal and negative affect
- Preoccupation and anticipation
What are the two theories of depemdence?
- Negative reinforcement models: Physical dependance theory, relates mostly to opiates, barbiturates and alcohol, based largely on increased tolerance and physical dependence
- Positive reinforcement models; positive incentive (reward) theory, relates mostly to coaine, amphetamine, nicotine, based largely on reward and reinforcement
What are the problems with the negtaive model?
Amphetamine, cocaine, nicotine form strong dependency but have relatively little withdrawal effect.
Alcohol and barbiturates have greater withdrawal but cause less dependance than heroine
Disuss speed of effect
Speed of effect seems to be critical for incentive
Heroine is biochemically converted to morphine in the body. Morphine isnt a greater cause of dependance becuase heroin enters the brain faster than morphine.
Injection > inhilation > absorption.
Crack cocaine (smoking) vs snorting cocaine (absorption)
crystal meth (smoking) vs desoxyn (time release methamphetamine HCl –last resort therapy for ADHD and narcolepsy)
What is dependancy often mediated through?
Dopamine neurtotransmitter action.
Amphetamine and cocaine produce their effects via dopamine release in specific neural pathways in the brain.
Opioids (morphine, heroine), MDMA (ecstacy), ethanol, PCP (angel dust), Nicotine (smoking) all ultimately prodice their effects via dopamine release in specific neural pathways in the brain
Food, Gambling, Internet,
Video Games, and sex, too
What is the key dependence/reward pathways in the brain that operate via dopamine neurotransmission?
- Dopamine signaling from the ventral tegmental area (VTA) to the nucleus accumbens (NA) is increased by drug action.
- Glutamate projections from the NA cause the prefrontal cortex to ‘remember’ the environment and behaviours which led to the reward
- Excess signalling of glutamate neurons in the prefrontal cortex stimulates the NA, triggering drug-seeking behaviours at the expense normal behaviours.
What is the environemntal relationship to relapse?
Dopamine release and sensitization creates a form of memory such that cues (drug paraphernalia, social situations) can induce dopamine release evem in the absense of the drug
What are the four catogories of drugs of misuse?
- Stimulants (cocaine, nicotine)
- Depressants (tranquilizers, alcohol)
- Opiods (heroin and methadone)
- Marijuana/ cannabis
How do stimulant drugs act?
Exert reinforcing activities via their direct role in dopamine management.
Cocaine inhibits the dopamine reuptake transporter
Amphetamines reverse the same transporter
Nicotine stimulates acetylcholine receptor neurons but these in turn stimulate dopaminergic neurons
So the net effects is chronmic dopamine flood into synapses and stimulation of dopamine receptors on target neurons
Unlike most drug-recptor interactions, those directly involving the dopamine system sensitise over time (contrast with tolerance). Sensitization leads to greater desire for next fix plus increased association with environmental cues that can trigger next fix/ relapse
What is the action of depressants ?
Barbiturates and benzodiazapines
Barbiturates heavily prescribes in 60/70s as sedative hypnotic anxiolytic drugs - caused dependancy
Phased out in favour of benzodiazepines eg diazepam, but these also cause dependance
Patient failure to adhere to prescribed doses can cause dependance
CNS develops tolerance to benzodiazapine sedation over a few months - leads to withdrawal
What is the action of alcohol and barbiturate depressant?
Actions are mediated by hyperexcitability of the inhibitory GABA receptors
What is the action of opioids?
Morphine blocks cAMP secondary messenger production, neurons try to redress cAMP balance. When morphine absense, too much cAMP generated. This sensitization induces withdrawal symptoms
What are the receptors for endogenous opiods?
Mu receptors prefer B-endorphine
Delta receptors prefer enkephalins
Kappa receptors prefer dynorphins
Mu receptors acted on by morphine, heroin and methadone
