Please enable JavaScript.
Coggle requires JavaScript to display documents.
(Drug Tolerance, Addiction: What Is It?, Drug Withdrawal Effects and…
Drug Tolerance
Specificity of drug tolerance
One drug can produce tolerance to other drugs that act by the same mechanism (cross tolerance).
Drug tolerance often develops to some effects of a drug but not to others.
Tolerance may develop to some effects while sensitivity to other effects of the same drug increases.
Drug sensitization
Drug tolerance is not a unitary phenomenon
There is no single mechanism that underlies all examples of it.
Tolerance to psychoactive drugs is largely functional
Reducing the number of receptors for it
Decreasing the efficiency of binding to existing receptors
Diminishing the impact of receptor binding on the activity of the cell.
Some of these changes caused by epigenetic mechanisms that affect gene expression
Demonstrated in two ways
By showing that given dose has less effect than it had before drug exposure
By showing that it takes more of the drug to produce the same effect.
Two categories of changes underlie drug tolerance
Metabolic tolerance
Results from changes that reduce the amount of the drug getting to its sites of action
Functional tolerance
Results from changes that reduce the reactivity of the sites of action to the drug
There is a shift in the dose-response curve to the right
A graph of the magnitude of the effect of different doses of the drug
State of decreased sensitivity to a drug that develops as a result of exposure to it.
Addiction: What Is It?
Addicts sometimes take drugs to prevent or alleviate their withdrawal symptoms
Is not the major motivating factor in their addiction.
Otherwise they could be easily cured with hospitalization
Most addicts renew drug taking even after months of enforced abstinence.
Addicts
Despite its adverse effects on their health and social life
Despite their repeated efforts to stop using it
Habitual drug users who continue to use a drug
Drugs aren’t the only substances to which humans are addicted
Bingeing on high-calorie foods
Compulsive gambling
Repeated illicit sex
May be based on same neural mechanisms.
Drug Withdrawal Effects and Physical Dependence
Effects are virtually always opposite to the initial effects of the drug.
Withdrawal of anticonvulsant drugs often triggers convulsions
Withdrawal of sleeping pills often produces insomnia.
Physically Dependent
Individuals suffering withdrawal reactions when they stop taking a drug
Withdrawal Syndrome
When it has been in body for several days in significant amounts
Adverse physiological reaction after sudden elimination of drug
Withdrawal effects can be produced by the same neural changes that produce drug tolerance
Drug is eliminated from the body
Compensatory neural changes, without the drug to offset them, manifest as withdrawal symptoms
These offset the drug’s effects and produce tolerance.
They are opposite to the initial effects of the drug
Exposure to a drug produces compensatory changes in the nervous system
Severity depends on:
Drug, duration, degree of drug exposure, speed of elimination
Longer exposure to greater doses and more rapid elimination produces greater withdrawal effects.
Drug Metabolism and Elimination
Drug metabolism
Actions of most drugs terminated by enzymes synthesized by the liver
Liver enzymes stimulate the conversion of active drugs to non-active forms
Drug metabolism eliminates a drug’s ability to pass through lipid membranes of cells
Drug can no longer penetrate the blood brain barrier
Other ways of eliminating small amount of drugs
Sweat
Feces
Urine
breath
Mother's Milk
Drug Penetration of the Central Nervous System
A protective filter: the blood brain barrier
Makes it difficult for many potentially dangerous blood-borne chemicals
To pass from the blood vessels of the CNS into its neurons.
After entering the bloodstream
Drug is carried in the blood
To the blood vessels of the central nervous system.
Mechanisms of Drug Action
Psychoactive drugs
Drugs that influence subjective experience and behavior by acting on the nervous system
Ways of influencing
Some act diffusely on neural membranes throughout CNS.
Others act more specifically
Binding to particular synaptic receptors
Influencing the synthesis
Transport, release, or deactivation of particular neurotransmitters
Influencing the chain of chemical reactions elicited in postsynaptic neurons by the activation of their receptors