Reading Wikipedia's article of dendrodendritic synapse, I find that:
Dendrodendritic synapses are activated in a similar fashion to axodendritic synapses in respects to using a chemical synapse. These chemical synapses receive a depolarizing signal from an incoming action potential which results in an influx of calcium ions that permit release of Neurotransmitters to propagate the signal the post synaptic cell. There is also evidence of bi-directionality in signaling at dendrodendritic synapses. Ordinarily, one of the dendrites will display inhibitory effects while the other will display excitatory effects.
Now I was wondering, does dendrodendritic synapse occur only when the neuron reaches the threshold action potential and "fires" or is it possible that dendrodendritic synapse occurs as a result of, for example, an axodendritic synapse at the same dendrite? (even though the neuron doesn't fire)
Clearly, we can see that the dendrite has multiple 'endings'. I was under the impression that a synapse can happen at any such 'ending'. Assuming that a synapse happens at one ending of the dendrite, is it viable that anything happens to a neighbouring neuron that is connected with a dendrodendritic synaptic connection to the other ending of the dendrite?