Evidence for presynaptic protein at the calyx of held nerve terminal

Presynaptic activity requires the localization and maintenance of thousands of proteins that are typically thought to be synthesized in the soma and transported to nerve terminals. However, local protein synthesis occurs at dendritic locations and local presynaptic protein synthesis has recently been shown to occur in an inhibitory neuron in the brain, but the small size of most nerve terminals complicates further studies. Here, we study presynaptic protein synthesis at the calyx of Held nerve terminal, located in the mammalian brain. The size of this terminal, its long axon, and high firing frequency make it an ideal choice to study presynaptic protein synthesis. We show a major ribosomal component, 5.8S ribosomal RNA is present in this presynaptic nerve terminal. To verify the presence of functional presynaptic ribosomes, we used the surface sensing of translation (SUnSET) technique. This produced well-defined fluorescent signals in presynaptic terminals and postsynaptic cell bodies, and the fluorescent signal was eliminated by inhibiting protein synthesis. To determine the effects on synaptic transmission, we measured electrical activity. After inhibiting translation, the initial frequency of spontaneous events increased by ~2-fold but the amplitude was unaffected, indicating a presynaptic mechanism. In addition, we find that evoked responses show less depression during high frequency firing (≥ 100 Hz). The reduction in depression is not consistent with effects on desensitization but is well explained by presynaptic changes in neurotransmitter release. These findings further indicate that presynaptic protein synthesis occurs, that it can affect spontaneous and evoked release of neurotransmitter, and it affects neurotransmitter release at high firing frequencies.Ph.D.Includes bibliographical referencesby Matthew Steven Scarnat