Week 3 (Receptors/Reuptake)

Page 23


Ionotropic Receptors

  • Rapid, brief on/off effect

  • Binding of a neurotransmitter causes it to twist

  • This opens the receptor to allow flow of certain ions

  • Ionotropic effects occur quicky


  • Most excitatory ionotropic synapses use glutamate

  • Most abundant neurotransmitter in the nervous system

  • Most inhibitory ionotropic synapses use GABA or glycine

  • Acetylcholine is often excitatory

  • Ionotropic effects are limited to a certain point on the membrane


Metabotropic Receptors

  • Slower, longer lasting complex effects

  • At rest metabotropic receptors are attached to a G protein

  • Binding a neurotransmitter to a metabotropic receptor causes the G protein to detach

  • This activates a second messenger which can have varied effects across the cell


  • Metabotropic effects onset 30ms after neurotransmitter binding

  • Metabotropic synapses use many neurotransmitters

    • Monoamines such as dopamine or serotonin

    • Amino acids like glutamate and GABA

  • Metabotropic effects can span across the whole cell


Neurotransmitter Inactivation

  • After a neurotransmitter has bound to a cell, it is either broken down or is detached

  • Otherwise it could continue effecting a receptor indefinitely

  • Some neurotransmitters are broken down by enzymes

    • Acetylcholine is broken down by the acetylcholinesterase

    • Most other transmitters are broken down by COMT


Neurotransmitters Reuptake

  • Other neurotransmitters detach and undergo reuptake

    • Membrane proteins called transporters bring the neurotransmitter back to the presynaptic neuron to be reused

    • Some drugs work by inhibiting reuptake


Negative Feedback

  • Negative feedback prevents the presynaptic cell from continuously releasing neurotransmitters

  • Auto receptors on the presynaptic cell

    • Responds to neurotransmitter release by inhibiting further synthesis and release of neurotransmitters

  • Some postsynaptic neurons release nitric oxide

    • This travels back to the presynaptic terminals and inhibits further neurotransmitter release