Hi Soledad,

depends on the optogenetic actuator. If you use an excitatory one this will lead to the release of the neurotransmitter of the affected cell. However if you use an inhibitory one (e.g. Halorhodopsin or Archaerhodopsin ) you hyperpolarize the cell and therefore supress its firing and transmitter release.

I hope this is of some help.

If your neuron is expressing an excitatory opsin (e.g., channelrhodopsin-2), then photostimulation of the soma with the appropriate wavelength (e.g., 470 nm) would result in depolarization of the neuron. Whether this depolarization would be sufficient to elicit an action potential, and whether the action potential would propagate down the axon and cause neurotrasmitter release in the synapse depends on a number of things (e.g., intra- and extracellular concentrations of ions, resting membrane potential of the stimulated neuron, amount of opsin expressed, viability of the axon...), but in most cases the answer to your question would be yes.

There is quite a range of cation conducting channelrhodopsins for exciting neurons with light. I can highly recommend CheRiff (from Adam Cohen's group - use blue light) or ChrimsonR (from Ed Boyden's group - use red light). Depending on expression/cell type you can very reliably drive APs with 1ms flashes up to about 50 Hz (exact intensity needed varies with wavelength - ChrimsonR needs higher intensity light than does CheRiff). Both are superior to ChR2 in several respects.