科研之友
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摘要
Non-technical summary It is accepted that learning involves creating or increasing the activity of existing chemical connections (synapses) between neurons. Some connections, known as 'silent synapses', have no detectable activity under resting conditions but can be switched on by electrical stimuli that mimic learning. To better understand how this occurs, we compared silent and active synapses in cultured neurons. When neurons were challenged with electrical stimulation, the extent of activation of previously active synapses was unchanged, whereas silent synapses were activated. Silent synapse activation did not correlate with increases in intracellular calcium (which evokes neurotransmitter release), but was dependent on the action of the enzyme protein kinase A. A large proportion of synapses in the adult brain are thought to be silent, and therefore a detailed knowledge of silent synapse activation could give insights into the mechanisms of learning and memory.Presynaptic long term potentiation of synaptic transmission activates silent synapses and potentiates existing active synapses. We sought to visualise these two processes by studying the cAMP-dependent protein kinase (PKA) potentiation of presynaptic vesicle cycling in cultured cerebellar granule neurons. Using FM dyes to label the pool of recycling synaptic vesicles, we found that trains of electrical stimulation which do not potentiate already active synapses are sufficient to rapidly activate a discrete population comprising silent and very low activity synapses. Silent synapse activation required PKA activity and conversely, active synapses could be silenced by PKA inhibition. Surprisingly, the recycling pool of synaptic vesicles in recently activated synapses was larger than in already active synapses and equivalent to synapses treated with forskolin. Imaging of synaptic vesicle cycling and cytosolic Ca2+ in individual nerve terminals confirmed that silent synapses have evoked Ca2+ transients comparable to those of active synapses. Furthermore, across populations of active synapses, changes in Ca2+ influx did not correlate with changes in the size of the pool of recycling synaptic vesicles. Finally, we found that stimulation of synapsin phosphorylation, but not RIM1 alpha, by PKA was frequency dependent and long lasting. These data are consistent with the idea that PKA regulates synaptic vesicle recycling downstream of Ca2+ influx and that this pathway is highly active in recently activated synapses.
- 出版日期2011-4-15
