HL2 Biology: E.4c Neurotransmitters & Drugs

Addiction to psychoactive drugs

  • Factors contributing to addiction:

1. Dopamine secretion: drugs that are addictive stimulate synapses involving dopamine, which makes the user feel pleasure because dopamine activates the reward pathway.
2. Genetic predisposition: although specific genes are still unknown, addiction to psychoactive drugs is thought to be hereditary, like with alcoholism
3. Social factors: cultural tradition, peer pressure, traumatic circumstances/experiences, deprivation, mental health issues can encourage and even enhance addiction to psychoactive drugs but it can also prevent it

  • Examples
    • Cocaine
      • Excitatory psychoactive drug
      • Highly addictive
      • Mechanism
        • once in the body, it binds to membrane proteins involved in reuptake of dopamine
        • dopamine cannot be absorbed by the presynaptic neuron anymore, resulting in an increased concentration of dopamine in the synapse
        • hence, cocaine users’ reward pathway is artificially stimulated, leading to constant euphoria
        • cocaine-induced depression can occur because of increased tolerance and adaptation by the body, which decreases the secretion of dopamine by the brain
      • Crack: vaporous so easy uptake into body and stronger effects
  • THC (tetrahydrocannabinol)
    • Chemical in cannabis that causes most of the psychoactive effects
    • Receptors are in many places in the brain
      • cerebellum, hippocampus, cerebral hemisphere
    • Mechanism
      • it binds to cannabinoid receptors, which is at a synapse where signaling chemicals are released by postsynaptic neuron to bind to presynaptic neuron
      • THC blocks release of excitatory neurotransmitters
      • hence, THC is an inhibitory psychoactive drug
    • General effects
      • psychomotor behavior, short-term memory is disrupted
      • appetite stimulated
      • other effects noted by users

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