The Human Brain : From Neurone to Nervous System

AXO-AXONIC SYNAPSES


  1. Axo-axonic synapses are synapses that end, not on the cell body, but on the terminal boutons of another neurone.
    They reduce the release of neurotransmitter by that bouton - hence their role in pre-synaptic inhibition

  2. The terminals of some neurones end on the terminal boutons of others: their neurotransmitter is released, not on to a post-synaptic cell soma or dendrite, but on to the terminal bouton of another neurone.

  3. This process results in the depolarisation of the post-synaptic bouton, which in turn reduces the calcium influx when the terminal is invaded by an action potential; the smaller calcium transient reduces the amount of transmitter released by the affected bouton.

  4. Presynaptic inhibition is largely mediated by glutamatergic metabotropic receptors..

  5. This arrangement allows the modulation of specific inputs to a post-synaptic neurone, i.e. selected nerve terminals on the post-synaptic neurone, by inhibiting the release of neurotransmitter by those specific endings.

  6. This is in contrast to post-synaptic inhibition that causes blanket inhibition of all inputs.

  7. Key Words: Synapses on boutons; pre-synaptic inhibition; modulation of individual synaptic inputs.