2. Introduction
Dopamine belongs to the family of catecholamines
Hormones Epinephrine and Norepinephrine (other catecholamines) are
derived from Dopamine
Significant role in learning, goal-directed behavior, regulation of
hormones, motor control
3. DA synthesis and metabolism
L phenylalanine (amino acid from diet)
phenyalanine hydroxylase
L- Tyrosine
Tyrosine hydroxylase RLS
L Dopa
Dopa decarboxylase
Dopamine (DA)
Monoamine oxidase (MAO)
Catechol-O-methyl transferase (COMT)
DOPAC + HVA
4. After synthesis, dopamine is packaged into synaptic vesicles via
the vesicular monoamine transporter (VMAT2) and stored there
until its release into the synapse during neurotransmission.
6. Metabotropic G-protein coupled receptors
D1 – like family:
Includes subtypes D1 and D5
Activation is coupled to Gαs ; activates adenylyl cylcase which
leads to increase in concentration of cAMP
D2 – like family:
Includes D2, D3 and D4
Activation is coupled to Gαi ; inhibits adenylyl cyclase leading to
decrease in concentration of cAMP
7. Receptor Locations Functions
D1 Found in high concentration in mesolimbic, nigrostratal and
mesocortical areas , such as substancia nigra, olfactory bulb, nucleus
accumbens, cuadate, putamen, striatum, Expressed in low level in
cerebellum, hippocampus, thalamus, hypothalamus, kidney
Voluntary movements, regulate growth and development,
regulations of feeding, affect, attentions, reward, sleep,
impulse control, reproductive behaviors, working memory,
learning, control of rennin in kidney
D2 Expressed in high levels in as substancia nigra, olfactory bulb,
cuadate, putamen, ventral tagemental area(VTA), nucleus accumbens
Found in low level in hypothalamus, septum, kidney, cortex, heart,
blood vessels, adrenal glands, gastrointestinal tract, sympathetic
ganglia
Involved in working memory, reward-motivation
functions regulate blood pressure, renal functions,
gastrointestinal motility, vasodilatations, regulate
locomotion-presynatic receptors inhibit locomotion and
post synaptic receptors activate locomotion
D3 Expressed only in CNS and it is not found outside the CNS. Found in
olfactory bulb, nucleus accumbens
Involved in endocrine function cognitions, emotions,
regulations oflocomotor functions and modulates
endocrine functions
D4 Substancia nigra, hippocampus, amygdala, thalamus, hypothalamus,
kidney, frontal cortex, heart, blood vessels, adrenal glands,
gastrointestinal tract, sympathetic ganglia, globus palidum, Lowest
receptor found in CNS than all dopamine receptors
Regulations of renal functions, gastrointestinal motility,
vasodilatations, blood pressure, modulations of cognitive
functions
D5 Substancia nigra, hypothalamus, hippocampus, dental gyrus, kidney,
heart, blood vessels, adrenal glands, gastrointestinal tract, sympathetic
ganglia
Involved in pain process, affective functions, endocrine
functions of dopamine
17. Dopamine and Reward Signaling
Behavior studies show that dopamine projections to striatum and
frontal cortex play important role in effect of rewards on learning
Dopamine neurons in the basal ganglia show increase in activity
when the animal receives an unexpected reward, or a cue that
predicts a reward and a decrease in activity when an expected
reward is not obtained
19. The dopaminergic projection to ventral striatum has often been
implicated in the mechanisms for addiction
Increased locomotor activity and stereotypy caused due to
psychostimulant involve dopamine release in striatum
Psychostimulants such as Cocaine and Amphetamine are known to
alter dopamine activity in brain
20. Impulsive cycle
Occasional substance use is an impulse choice driven by positive
reinforcement of the drug’s expected effect
This teaches the brain to anticipate reward on subsequent exposure
to the drug
When the substance is taken, pleasure will be experienced again,
usually followed by regret
21. Compulsive cycle
With repeated exposure to the drug neurobiological changes occur in
the brain
leads to craving,
reduced reward on drug exposure
withdrawal during abstinence
(negative reinforcement)
This leads to craving which is
released by drug ingestion
22. Attention deficit hyperactivity disorder
Decrease In Dopamine Level in Anterior frontal cortex
An area associated with cognitive function such as
Attention
Concentration
23.
24. Schizophrenia
Defective dopamine neurotransmission – relative excess of central
dopaminergic activity
An increase in DA function in the mesolimbic system (postive symptom)
Decreased function in the mesocortical DA system (negative symptoms)
Behavior similar to the behavioral effects of psychostimulants
25. ANTIPSYCHOTIC DRUGS
1) Phenothiazines
Aliphatic side chain: Chlorpromazine
Piperidine side chain: Thioridazine
Piperazine side chain: Trifluoperazine Fluphenazine
All antipsychotics (except clozapine-like atypical) have potent dopamine D2
receptor blocking action; antipsychotic potency has shown good correlation
with their capacity to bind to D2 receptor.
Phenothiazines and thioxanthenes also block D1, D3 and D4 receptors,
but there is no correlation with antipsychotic potency.
Blockade of dopaminergic projections to the temporal and prefrontal areas
constituting the ‘limbic system’ and in mesocortical areas is probably
responsible for the antipsychotic action.
26.
27.
28. Role of dopamine o prolactin secretion
Inhibits secretion of prolactin by acting on D2 receptors.
Treatment of hyperprolactinemia
Ergot derivatives : bromocriptine, cabergoline, pergolide.
Non ergot : Quinagolide
29. References
Rang H.P. and Dale M.M;Antipsychotics;7th edition; 39,45,49; 557
http://en.wikipedia.org/wiki/Dopamine