Drug Effects on Synapses (AQA A Level Biology): Revision Note

Predicting the effects of drugs on synapses

• Drugs of many kinds may impact synaptic transmission, e.g. by:

  • stimulating the release of a neurotransmitter

  • providing the chemicals needed to synthesise neurotransmitters

  • imitating a neurotransmitter by binding to the same specific receptor

  • preventing the reuptake of the neurotransmitter by the presynaptic neurone

• Examples of drugs that affect synapses include:

  • dopamine agonists and precursors

    • People with Parkinson’s disease do not produce enough dopamine in specific parts of the brain

    • Treatment options include:

      • dopamine agonists: drugs that bind to dopamine receptors and produce the same effect as dopamine

      • dopamine precursors: substances that can be converted into dopamine inside neurones, increasing dopamine levels in the brain

  • morphine

    • Morphine mimics the structure of naturally occurring chemicals called endorphins

    • Morphine binds to endorphin receptors and stimulates dopamine release, which leads to pain relief and a feeling of pleasure.

  • cocaine

    • Cocaine binds to dopamine transporter proteins on the presynaptic membrane

    • This blocks the transporters and prevents reabsorption of dopamine, causing dopamine to build up in the synapse

    • The postsynaptic neurone is overstimulated, producing feelings of pleasure

  • cannabinoids

    • Cannabinoids bind to receptors on the presynaptic membranes of neuromuscular junctions, causing calcium ion channels to close

    • Release of neurotransmitters is reduced, weakening muscle contraction

  • MDMA

    • MDMA stimulates the release of several neurotransmitters, most notably serotonin

    • Taking MDMA can therefore alter mood