Dopamine - PowerPoint PPT Presentation

1 / 25
About This Presentation
Title:

Dopamine

Description:

Dopamine Structure and Function John Hill and Natalia Toporikova What is Dopamine? Dopamine (DA) is a monoamine neurotransmitter that upon binding to a dopamine ... – PowerPoint PPT presentation

Number of Views:4007
Avg rating:5.0/5.0
Slides: 26
Provided by: John576
Category:
Tags: dopamine

less

Transcript and Presenter's Notes

Title: Dopamine


1
Dopamine
  • Structure and Function
  • John Hill and Natalia Toporikova

2
What is Dopamine?
  • Dopamine (DA) is a monoamine neurotransmitter
    that upon binding to a dopamine receptor
    (G-protein coupled) releases a variety of
    downstream signals.

3
Dopamine synthesis
Precursor of dopamine is amino acid tyrosine
4
Where is Dopamine formed?
  • Dopamine is mainly synthesized in areas of the
    central and peripheral nervous systems, such as
    in the hypothalamus, the arcuate nucleus, and the
    caudad

5
How does dopamine work?
  • Dopamine is released into synaptic cleft.
  • Dopamine binds with receptor.
  • Once done, dopamine is taken back into the cell,
    so not too much is present in the cleft.
  • The control mechanism for this signaling is found
    in the endorphin (pink).
  • Endorphin can either enhance of inhibit the
    action of dopamine.

Note this is similar to what we learned about
acetylcholine release.
6
What are the Functions of Dopamine?
  • Dopamine plays a significant role in the
    cardiovascular, renal, hormonal, and central
    nervous systems. It is thought 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 a and ß adrenergic and
    dopaminergic receptors (D1 and D2)

7
Functions of Dopamine in the Body
  • Function depends on type of receptor.
  • Involved in pleasure (cocaine blocks its
    reuptake)
  • Involved in motor control of muscles in body.
  • Assists in normal brain function (thoughts)
  • Induces emotions.

8
Dopamine-related diseases
  • Dopamine deficiency in the striatum or substantia
    nigra results in Parkinsons-like symptoms. In
    this case, movement becomes slow and rigid,
    accompanied by muscle tremor.
  • An excessive amount of dopamine is affiliated
    with schizophrenia, characterized by altered
    behavior, and delusions.
  • A deficiency of dopamine (DA) is a leading
    candidate for the etiology of certain symptoms of
    depression.

9
Research involving dopamine
  • May have a role in obesity
  • May play a role in drug addiction
  • May have a role in alcoholism
  • May use dopamine derivatives to treat disease

10
Drugs can stimulate dopamine receptors
  • Some drugs are known as dopamine agonists.
  • These drugs bind to dopamine receptors in place
    of dopamine and directly stimulate those
    receptors.
  • They can stimulate dopamine receptors even in
    someone without dopamine neurons.

11
Drugs can fail to stimulate dopamine receptors
  • Antagonists are drugs that bind but don't
    stimulate dopamine receptors.
  • Antagonists can prevent or reverse the actions of
    dopamine.
  • They prevent dopamine from attaching to
    receptors.

12
Drugs can act directly or indirectly on dopamine
receptors
  • Drugs such as cocaine and amphetamine produce
    their effects by changing the flow of
    neurotransmitters.
  • These drugs are defined as indirect acting
    because they depend on the activity of neurons.

13
Drugs can act directly or indirectly on dopamine
receptors
  • In contrast, some drugs bypass neurotransmitters
    altogether and act directly on receptors.
  • Such drugs are direct acting.
  • Direct agonists stimulate dopamine receptors even
    when dopamine neurons are missing.

14
Two ways to affect dopamine levels
  • Some drugs increase dopamine by preventing
    dopamine reuptake, leaving more dopamine in the
    synapse (i.e., cocaine, methylphenidate)
  • While another drug helps to release more dopamine
    (amphetamine).

15
How cells adapt to previous drug exposure
  • Long-term treatment with dopamine antagonists
    increases the number of dopamine receptors.
  • The receptors themselves become more sensitive to
    dopamine.
  • This process is called sensitization.

16
How cells adapt to previous drug exposure
  • Overstimulation decreases the number of
    receptors, and the remaining receptors become
    less sensitive to dopamine.
  • This process is called desensitization.

17
Disease and drugs can produce faulty sensitization
  • Sensitization or desensitization normally occurs
    with drug exposure. However, addiction can
    tamper with the reuptake system.
  • This disrupts the normal levels of
    neurotransmitters in the brain and can lead to
    faulty desensitization or sensitization.

18
Reward pathway
  • Dopamine neuron connected with part of the brain
    that is activated by natural rewards and by
    artificial rewards such as addictive drugs.
  • This part of the brain is called the reward
    system.

19
How reward pathway works
  • This pathway is activated by a rewarding
    stimulus.
  • The dopamine system compares the brain
    expectations of reward with what is actually
    happening at the moment.
  • If the reward is higher than predicted, dopamine
    is sent to many parts of the brain, giving the
    green light to action to get more reward.

20
Cocaine addiction
  • Cocaine binds to the uptake pumps and prevents
    them from removing dopamine from the synapse.
  • More dopamine in the synapse, and more dopamine
    receptors are activated.

21
Cocaine addiction
  • The increased activation of dopamine receptors
    causes increased production of cAMP inside the
    post-synaptic cell. This lead to abnormal firing
    patterns.
  • With continued use of cocaine, the body relies on
    this drug to maintain rewarding feelings.

A PET Scan (glucose uptake)
22
Nicotine addiction
  • Nicotinic acetylcholine receptors respond to
    nicotine as it enters the body after smoking a
    cigarette.
  • That burst of activity in the neurons causes
    dopamine release that contributes to the
    sensation of pleasure.
  • Over time some nicotinic receptors desensitize,
    even though nicotine is still present.

23
Nicotine addiction mechanism.
  • The first cigarette of the day gives smokers
    their first exposure to nicotine in 8-10 hours,
    so the neurons experience an extreme burst of
    activity.
  • The dopamine system gives the signal to get more
    reward (cigarette).
  • Later in the day there will be a mixture of the
    receptors being desensitized and activated, so
    that a smoker will not get the same large burst
    of activity and pleasure that the first cigarette
    provides.

24
Food addiction
  • Obese people have about 20 fewer receptors for
    the chemical dopamine in the area of the brain
    that regulates reward.
  • Desensitization may trigger overeating in an
    effort to stimulate the reward pathway.

25
Conclusion
  • Dopamine plays a major role in addiction.
  • The activation and deactivation of dopamine
    receptors can lead to activation of the brain
    center responsible for pleasure.
  • Dopamine is a key element in the reward system -
    the expectation of reward can change behavior.
Write a Comment
User Comments (0)
About PowerShow.com