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Drugsandthe Brain Part1 Review
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Drugsandthe Brain Part1 Review

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  • 1. Drugs and the Brain Part 1 Neurotransmitter Review
  • 2. Spectrum of Neurotransmitters
    • There are at least 50 distinct neurotransmitters that carry messages in the brain
    • Only a few have been well studied
    • Virtually all drugs used in psychopharmacology today target one of the 5 well studied neurotransmitters
    • Neuropharmacology is in its infancy; future developments are likely to be extensive
  • 3. A Review of Major Neurotransmitters
    • Norepinephrine -
      • One of two major catecholamines – transmitter of the sympathetic nerves of the autonomic nervous system which controls emergency responses (fight or flight)
    • Dopamine –
      • A catecholamine transmitter. A major transmitter in the corpus striatum, a part of the brain regulating motor behavior. Destruction of these neurons causes Parkinson’s. Blockade of actions of dopamine in other brain areas is mode of action of some antischizophrenic drugs.
    • Serotonin –
      • Transmitter of a group of neurons in the raphe nuclei of the brain stem. Actions of psychedelic drugs are due to changes in activity of serotonin neurons
  • 4. A Review of Major Neurotransmitters (continued)
    • Acetylcholine –
      • Neurotransmitter at neuromuscular junctions for all voluntary muscles, as well as many involuntary synapses. Exact role in brain still unclear
    • GABA –
      • Occurs almost exclusively in the brain. Inhibitory transmitter that reduces firing of neurons
    • Glycine –
      • Serves as an inhibitory neurotransmitter in small neurons in the spinal cord and brain stem
  • 5. A Review of Major Neurotransmitters (continued)
    • Glutamic Acid –
      • An amino acid that also functions as a neurotransmitter. Probably the major excitatory neurotransmitter in the brain. Acts at several receptor subtypes. May be responsible for damage associated with stroke.
    • Nitric Oxide –
      • Transmitter of nerves to the intestines and other organs. May regulate emotional behavior in brain.
  • 6. A Review of Major Neurotransmitters
    • Endorphins –
      • Endogenous morphine-like substances. Any substance that produces opiate-like effects. Includes (& is sometimes a synonym for) enkephalins.
    • Enkephalins –
      • 2 peptides, each containing 5 amino acids, that act at opiate receptors in the brain. Analgesics.
    • Substance P –
      • A peptide containing 11 amino acids. A major transmitter of sensory neurons which convey pain from the periphery to the spinal cord. Opiates block release. Also found in brain.
  • 7. How Drugs Effect Neurotransmitters
    • Effects can occur at many stages in the process
    • May block the action of an enzyme required to synthesize a neurotransmitter from a precursor molecule
      • Many drugs to lower blood pressure work by decreasing synthesis of norepinephrine
    • May cause neurotransmitters to leak from synaptic vesicles, where they are degraded by enzyme
      • Resperine interferes with storage of norepinephrine this way (tranquilizer, lowers blood pressure)
  • 8. How Drugs Effect Neurotransmitters (Cont.)
    • May effect the release of transmitters from nerve endings
      • Slip into vesicles, pushing neurotransmitters out into the synaptic cleft
      • Amphetamines release norepinephrine & dopamine this way
    • Other drugs block the release process itself
    • Some drugs inhibit enzymes that degrade neurotransmitters, increasing the level of transmitter present in the synapse and facilitating transmission
      • Most antidepressants work this way
      • MAOI – monoamine oxidase inhibitors inhibit enzyme which degrades transmitters responsible for mood stabilization
  • 9. How Drugs Effect Neurotransmitters (Cont.)
    • Others block re-uptake
      • Tricyclics
      • SSRIs & SNRIs
    • May influence the neurotransmitter receptor
      • May resemble transmitter and mimic effect at the receptor
      • May occupy the receptor without causing any 2 nd messenger response in the nerve
      • Blocks access of neurotransmitter to receptor
  • 10. Location of Drug Action
    • Where in the brain a drug acts is critical
    • Each transmitter can bind many locations, has multiple effects; side effects can be considerable
      • Example: Acetylcholine
      • Many insecticides target acetylcholinesterase, the enzyme that breaks down acetylcholine; can cause death in children by stopping breathing
      • Belladona – Plant used since ancient times for stomach upset, slows intestinal contractions. Overdose can cause memory loss, death. Active ingredient, atropine, blocks acetylcholine.
      • Acetylcholine deficiency is implicated in memory loss. Acetylcholine-rich neurons of the basal nucleus destroyed in Alzheimer’s patients. Drugs that inhibit acetylcholinesterase improve memory & are used in Alzheimer’s patients.

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