2. • Dopamine?
- neurotransmitter?
- reward system
- related diseases
• ADHD?
• Alcohol? (pathway with dopamine)
• ADHD- alcohol?
• Dopamine – ADHD – alcohol?
• Related reports
- epigenetic, dopaminergic, …
• Epigenetic project
3. • Vesicle release process:
docking → priming → fusion
• Proteins involved in
presynaptic exocytosis
• SNARE proteins: docking
(membs close together before
fusion)
• Synaptotagmin (vesicle protein)
- Ca2+ sensor triggering fusion
4. I. Small molecule NT
① acetylcholine
② Amino Acids
• glutamate
• GABA & glycine
③ Biogenic amines
• dopamine, norepinephrine (noradrenalin), epinephrine (adrenalin),
serotonin (5-hydroxy tryptamine, 5-HT), histamine
④ Purines: ATP
II. Peptides
• Substance P, CGRP(calcitonin gene related peptide), Enkephalin,
Cholecystokinin(CCK), etc.
• Opioid peptides
• Substance P
III. Gaseous NT – Nitrous oxide, Carbon monoxide
5. 1) Acetylcholine R
① Nicotinic: Ionotropic cys-loop superfamily
② Muscarinic: Metabotropic family R (M1~M5)
2) Inhibitory amino acid R: Ionotropic (GABAA,C & Gly), metabotropic (GABAB)
3) Excitatory amino acid R: Glutamate : NMDA, Kainate, AMPA
4) Purine (ATP) R: Ionotropic (P2X) & metabotropic (P2Y), presyn adenosine-R
5) Biogenic amine R: metabotropic except 5-HT3 (Ionotropic cys-loop superfamily)
6) Neuropeptides R: metabotropic R, diffused extracellular NT, more sensitive
7) Gas NT R: NO, CO - no binding to R, enzyme activation, modification of
protein activity by nitrosylating
6. Synthesis Storage and release Receptor binding Degradation
A. Release and degradation of the NT inside
the axon terminal
B. Increased NT release into the synapse
C. Prevention of NT release into the synapse
D. Inhibition of synthesis of the NT
E. Reduced reuptake of the NT from the
synapse
F. Reduced degradation of the NT in the
synapse
G. Agonist (evoke same response as
neurotransmitter) or antagonists (block
response to neurotransmitter) can occupy
the receptors
H. Reduced biochemical response inside the
dendrite
7. Amine Compounds: Serotonin, Noradrenalin and Dopamine
These are the brain chemicals that to malfunction when stress levels become
more than a person can handle
8. Norepinephrine (NE)
• noradrenergic neurons in the locus ceruleus and nucleus subceruleus
• PNS: Smooth muscles, cardiac muscle and glands
- Increase in blood pressure, constriction of arteries
• CNS: General behavior
Serotonin (5-HT)
• serotonergic neurons in the raphe nuclei
• Regulation of mood, behavior, appetite, and cerebral circulation.
• SSRIs (serotonin-specific reuptake inhibitors):
– Inhibit reuptake and destruction of serotonin, prolonging the action of NT
– Used as an antidepressant
– Reduces appetite, treatment for anxiety, treatment for migraine headaches
Histamine
• Histaminergic neurons in tuberomammillary n. of hypothalamus Epinephrine
• Adrenergic neurons in rostral medulla
Epinephrine
• Adrenergic neurons in rostral medulla
9. Dopamine (DA) is a monoamine neurotransmitter that upon binding to
a dopamine receptor (G-protein coupled) releases a variety of downstream signals.
Where is dopamine formed/produced?
Mainly in areas of the central and peripheral nervous systems, such as in the
hypothalamus, the arcuate nucleus, and the caudad.
What are the functions of dopamine?
In the cardiovascular, renal, hormonal, and central nervous systems.
To control processes as diverse as
movement to drug addiction.
Dopamine dendrites extend into
various regions of the brain,
controlling different functions through
the stimulation of α and β adrenergic
and dopaminergic receptors (D1 and D2)
(Velasco et al., 1998).
11. DAT (The dopamine transporter)
regulates the uptake of dopamine
into neurons.
Dopamine is thought to bind to DT
via a separate binding domain that
is constructed of multiple amino
acid residues. These amino acid
residues are not present in the
primary structure of DT, but are
thought to have interactions with
the protein in its tertiary form.
MAO (monoamine oxidase)
breaks down free dopamine
(not contained in a vesicle).
MAO play a role in recycling the
components of dopamine, but it
also keeps the concentration of
dopamine lower than the rate at
which it is being produced.
12. • Dopaminergic neurons in the two main brainstem regions
− substantia nigra pars compacta & ventral tegmental area (VTA)
a. Nigrostriatal dopamine system:
• Neurons in substantia nigra
send fibers to corpus striatum.
• Initiation of skeletal muscle movement.
• Parkinson’s disease: degeneration
of neurons in substantia nigra.
b. Mesolimbic dopamine system:
• Neurons originate in midbrain,
send axons to limbic system.
• Involved in behavior and reward.
• Addictive drugs: promote activity
in nucleus accumbens
c. Meso-cortical pathway
• negative symptoms (motivation and emotional response)
d. Tubulo-infundibular pathway (endocrine related, prolactin)
13. • The mesolimbic dopamine path correspond to the parts of the limbic system,
which are connected to emotions and is responsible for the ability to learn,
the short-term memory, maintenance of moods and the alignment of
thought and action.
• The mesolimbic system represents a modulation system, a filter and gating
system for signals coming from the limbic system and for signals which
maintain the basic functions of life and motivation (Koob 1992).
• The Nucleus accumbens,
- the most important end point of the mesolimbic dopamine path.
- a clearing centre for signals coming from the limbic system
- the switching point, which anticipates the probability of reward-stimuli and
steers the attention of the nerve system.
16. • Dopamine deficiency in the striatum or substantia nigra :
Parkinson’s-like symptoms.
- movement becomes slow and rigid, accompanied by muscle tremor.
- L-DOPA have been created to supplement the quantity of dopamine in the
brain (Katzenschlager et al., 2002).
• An excessive amount of dopamine :
Schizophrenia
- characterized by altered behavior, and delusions.
- Cocaine, block the return of dopamine into the brain,
resulting in a build up of dopamine in the synapse,
leading to drug-induced psychosis or schizophrenia.
Tourett’s syndrome, ADHD
17. • The most commonly dignosed neuropsyciatric disorder in child hood
• ADHD wanes with age, symptoms can persist into adolescence and adulthood.
• The incidence in children : 3% ~ >5% (Biederman 1998)
• The diagnosis of ADHD : is currently based on DSM-IV criteria.
• The core symptoms : impulsivity, inattention, motor restlessness
• Heterogenous clinical symptoms, comorbidity (approx. 65%)
with other disorders (conduct, mood, bipolar and anxiety disorders, Tourette’s)
• Abnormal morphology and function of ADHD brains, detected primarily by
magnetic resonance imaging, converge on the catecholamine-rich frontal cortex
and subcortical neural networks
19. • On the basis of the following lines of evidence, the DAT is one of several lead
candidates for investigating the pathophysiology of ADHD and anti-ADHD drug
mechanisms:
1) dopamine transport inhibitors indirectly activate dopamine receptor subtypes;
D4 and D5 dopamine receptors are implicated in ADHD, and dopamine
receptor activity enhances attention and experiential salience and engenders
stimulation
2) the DAT is a selective and principal target of the most widely used
antihyperactivity medications (amphetamine and methylphenidate)
3) the DAT gene is associated with ADHD
4) in some studies, abnormal levels of the DAT have been detected in brains of
ADHD subjects.
20. • Dopamine is released from both dendrites and axons and might activate
receptors locally or remotely through volume transmission.
• The DAT limits the duration of synaptic activity and diffusion by sequestering
dopamine into neurons (Cragg and Rice 2004).
• The DAT is present on cell bodies, dendrites, and axons but apparently is not
localized in the immediate active zone of the synapse (Hersch et al 1997)
• Accordingly, the DAT might reduce dopamine overflow into perisynaptic regions
but not robustly sequester dopamine within the synapse.
• Overexpression of the DAT might lead to compensatory increases in dopamine
release, a reduction in extracellular dopamine levels, or altered cellular
distribution of the DAT.
21. Monoamine Neurotransmitter Transporters
Extracellular neurotransmitter concentrations are regulated, in part, by monoamine
transporters that sequester dopamine (DAT), serotonin (SERT), and norepinephrine
(NET) into neurons.
The majority of specific genes implicated in ADHD encode components of
catecholamine signaling systems.
The critical role of monoamine transporters for normal brain function is
underscored by the wide range of drugs that target monoamine transporters,
including medications for depression, ADHD, smoking addiction, obsessive-
compulsive disorder, and sleep disorders.
DAT is one of several
genes implicated
ADHD
22. • DAT is a principal target of the most
widely used antihyperactivity medications
(amphetamine and methylphenidate).
• All current anti-ADHD drugs modulate DA
and NE levels in brain regions expressing
DAT and NET. The majority of these drugs
interfere with transporter-mediated
clearance of extracellular neurotransmitters.
• Interfere with DAT by brain-region- and
drug-specific mechanisms indirectly
activating DA and possibly NE-R subtypes
raising extracellular DA levels in DAT-
rich brain regions enhancing attention
and experiential salience.
• Repeated use of certain transport
inhibitors (cocaine…), can eventually result
in compulsive drug-seeking behavior.
23. • At the molecular level, the 12-membrane–spanning DAT protein contains a large
extracellular loop, with consensus sites for glycosylation that function to
regulate DAT trafficking and stability (Li et al 2004).
• Similarly, glycosylation of the NET controls stability, trafficking, and transport
activity (Melikian et al 1996). Potential phosphorylation sites (serine, threonine,
and tyrosine) might also acutely modulate DAT trafficking.
24. • A length or of sequence in the 3=-untranslated region of the DAT gene might
affect DAT expression.
• A fixed length–repeat sequence, by number of repeats from 3 to 11.
10 repeats sequences are the most common
• Inheritance of this repeat length in both alleles is associated with ADHD in some
studies but accounts for less than 4% of the variance.
• Intragenic allelic interactions might distinguish haplotype functional diversity,
and association studies might inadvertently group haplotypes of different
function together on the basis of VNTR length.
The DAT Gene Variants
25. • DAT control of dopamine release is region specific.
- In the striatum, dopamine clearance is a primary function of the DAT,
whereas in the substantia nigra the DAT regulates extracellular dopamine
levels by controlling both clearance and release.
• The complexity of region-specific DAT function is relevant to the pharmacologic
effects of anti-ADHD drugs.
• Methylphenidate blocks dopamine transport, whereas amphetamine is a
substrate for the DAT and presumably can trigger dopamine release
in the substantia nigra.
• These positron emission tomography
(PET) scans show that patient with ADHD
had lower levels of dopamine
transporters in the nucleus accumbens ,
a part of the brains reward center, than
control subjects
26. Main Effects:
• Alcohol mainly acts on GABA
receptors (GABA receptors down
regulate the NT release of neurons,
essentially reducing neural activity) by
keeping its Cl- receptors open longer
than they normally would be.
• This causes GABA receptors to have
an increased effect and reduces
neural activity resulting in the calm,
sleepy feeling.
• Alcohol also inhibits glutamate
receptor function which causes
slurred speech, memory deficits, and
discoordintaion.
27. Secondary Effects:
• Raises the endorphin levels
- causes the analgesic
affect (pain killing).
• Increases the amount of
dopamine in the brain –
contributes to the addictive
qualities.
30. • Can affect the methionine– homocysteine cycle by disrupting the enzymes
required for methionine metabolism, thus interfering with SAM dependent
methylation reactions.
• Alcohol and its breakdown products (i.e., metabolites such as acetaldehyde)
also cause different site specific modifications in histones.
• Changes in the acetylation and methylation patterns of specific histones
resulting from chronic alcohol feeding and high blood alcohol levels can lead
to persistently altered gene expression and thus may play a role in this
“epigenetic memory.”
• May reduce the absorption of folate, a key component of the methionine–
homocysteine cycle, thereby influencing methylation capacity.
31. • During prenatal and early postnatal development, the epigenome is highly
susceptible to environmental stimuli such as diet, drugs, environmental agents,
and maternal behavior.
• Preconception, preimplantation, and gastrulation
- Appear to be particularly sensitive to the teratogenic effects of alcohol,
- The clinical variability of FASD may be related not only to the dose of alcohol
but also to when alcohol exposure occurs in relation to developmental periods.
• Gastrulation appears to be most sensitive to teratogenic insults- a wide range
of adverse effects (morphological and behavioral abnormalities)
• Both preconception and preimplantation alcohol exposure can cause adverse
effects, even though the embryo is not directly exposed to alcohol at this stage
because it is not yet implanted in the uterus and therefore not connected to or
nourished by the maternal system, probably provides the most compelling
evidence of a role for epigenetic mechanisms in the outcomes observed.
32. Maternal effect
Paternal effect
(preconceptional/
(preconceptional)
prenatal)
- How long ?
- How severe ?
- Epigenetic target ?
- DAT ?
- SERT ?
- MecP2 ?