mechanism of drug addiction

1. A SEMINAR ON
THE PHYSIOLOGY OF DRUG
ADDICTION
BY,
DAWN V TOMY. (M.PHARM)
RVS COLLEGE OF PHARMACEUTICAL SCIENCES, SULUR
COIMBATORE 1

2. INTRODUCTION TO DRUGS
WHO DEFINITION “A drug is any
substance or product that is used or
intended to be used to modify or explore
physiological systems or pathological
states for the benefit of the patient.
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3. DRUGS OF ABUSE
SF
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4. NERVOUS SYSTEM
1.CENTRAL NERVOUS SYSTEM.
2.PERIPHERAL NERVOUS
SYSTEM.
A. AUTONOMIC NERVOUS SYSTEM.
i. SYMPATHETIC SYSTEM.
ii. PARASYMPATHETIC SYSTEM.
B. SOMATIC NERVOUS SYSTEM.
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6. NEURONS
Neurons are the basic unit of nervous system.
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8. NEUROTRANSMITTERS
EXCITATORY TRANSMITTERS.
GLUTAMATE, ASPARTATE.
INHIBITORY TRANSMITTERS.
GABA, GLYCINE.
OTHERS.
NORADRENALINE, ADRENALINE, DOPAMINE, SEROTONIN,
ACTYLCHOLINE, HISTAMINE, ENDOCANNOBINOIDS -
ENDOGENOUS OPIOID PEPTIDES - ENKEPHALINS,
ENDORPHINS, DYNORPHINS.
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9. RECEPTORS
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11. DRUGS ON RECEPTORS
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12. SOME TERMINOLOGIES
• Addiction [Substance abuse] = Psychological +
Physiological dependence
• Psychological = compulsive drug seeking, craving
• Physiological = symptoms and signs opposite to
drug.
• Tolerance.
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13. SOME TERMINOLOGIES
Reinforcement: Tendency of a pleasure-
producing drug to lead to repeated self
administration
Withdrawal- Drug is suddenly stopped
develop a withdrawal syndrome
characterized by craving, dysphoria,
signs of sympathetic overactivity.
Rebound - Drug- suddenly stopped— their
symptoms come back in an exaggerated
fashion.
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14. ADDICTION
• Addiction is a state in which a person engages in
a compulsive behavior, even when faced with
negative consequences.
• The behavior is rewarded and reinforced via the
reward pathway.
• A major feature of addiction is the loss of control
in limiting intake of the substance or behavior.
• Addiction is a chronic, relapsing disease resulting
from fundamental changes in the brain.
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15. YOUR BRAIN ON DRUGS
• All addictive drugs produce their effects by
altering the synaptic activity.
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17. DOPAMINE IS THE LINK IN ADDICTION
• Addictive drugs are biochemically quite
different
– Activate different neurotransmitter systems
– Produce different psychoactive effects
– Heroin acts on the opiate system
– Nicotine acts on the cholinergic system
– Cocaine acts on dopaminergic & noradrenergic
systems
• All either stimulate dopamine release (heroin,
nicotine) or enhance dopamine action
(cocaine) in the nucleus accumbens.
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18. THE REWARD PATHWAY
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19. THE REWARD PATHWAY
• The reward pathway is in the limbic system
consisting of the nucleus accumbens, ventral
tegmental area (VTA) and the prefrontal cortex.
• The neurons of the VTA contain dopamine
which is released into the nucleus accumbens
and prefrontal cortex in response to natural or
artificial reward stimuli.
• Stimulation of the reward pathway produces
highly pleasurable sensations, providing positive
reinforcement which promotes further drug use.
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20. TYPES OF REWARD SYSTEMS
• Reward system is of 2 types.
1. Natural reward system.
2. Artificial reward system.
• “NATURAL” rewarding stimulus (e.g., food, water, sex,
nurture) or “ARTIFICIAL” rewarding stimulus (e.g.,
drugs), information travels from the VTA to the nucleus
accumbens and then up to the prefrontal cortex.
• VTA contain dopamine which is released in
the nucleus accumbens and in the prefrontal
cortex. 20

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22. DRUGS ACT IN DIFFERENT
PARTS OF THE PATHWAY
• Heroin & nicotine act on the VTA.
– These dopaminergic neurons have both
opiate and nicotinic acetylcholine receptors.
• Cocaine acts on the nucleus accumbens.
– The nucleus accumbens is a target of the
ascending dopaminergic axons in the
forebrain.
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23. Alcohol
Decreases the actions of the
excitatory NMDA receptor
complex, i.e., it diminishes
excitation.
•Enhances G B i nhi bi t i on.
AA
•R educes gl ut am e exci t at i on.
at
•Enhances euphor i c ef f ect s by
r el easi ng O at es and
pi
endocannabi noi ds, t her eby
m at i ng i t s "hi gh."
edi 23

24. DRUG ABUSE AND ADDICTION
SELF ABUSE: REWARD PATHWAY.
ADDICTION: CHANGES IN THE
NEUROBIOLOGY OF THE BRAIN ON
REPEATED ADMINISTRATION.
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25. THE MESOLIMBIC DOPAMINERGIC REWARD PATHWAY
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26. DRUG TOLERANCE
• When a substance is used repeatedly over
time, tolerance may develop.
• The brain adjusts its chemistry to offset the
effects of the drug and tolerance develops.
• As tolerance develops, more of the drug is
needed to produce the same effects.
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27. SUBSTANCE DEPENDENCE
• Substance dependence develops when
neurons adapt to repeated drug use and only
function normally in the presence of the drug.
• When dependency develops, the brain has
become dependent upon the substance to
function.
• Without the substance the user experiences
withdrawal and intense cravings for the
substance.
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28. REWARD DEFICIENCY
• Prolonged drug use causes the dopamine
neurons in the reward pathway to cease
functioning.
• This state of dopamine deficiency causes the
user to experience chronic feelings of anxiety,
depression and an inability to just feel good.
• The person can only feel normal when under the
influence of the drug.
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29. ADDICTION VS. DEPENDENCE
• It is possible to be dependent on a drug without
being addicted. Although, if one is addicted
they are most likely also dependent.
• For example; A terminal cancer patient being
treated with morphine for pain will experience
withdrawal if the drug is stopped, but they are
not a compulsive user of the drug therefore
they are not addicted.
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