While dendritic neurotransmitter release is one function,
backpropagating APs are also considered important in other phenomena.
One important thing to consider is that backpropagation can have two
separate mechanisms: A merely passive electrotonic spread of
actionpotentials from the soma/initiation site into the dendrites. This
is often weak and not found in all neurons. Alternatively, voltage
sensitive ionchannels in the dendrites can cause an active
One role of backprops is the unblocking of NMDA-channels at synapses,
allowing them to open when they are activated by glutamate released from
the presynapse. This coincidence of pre- and post-synaptic activity can
lead to changes in the strength of the involved synapses.
You might want to have a look at:
M. London and M. Häusser. Dendritic computation. Annual Reviews
Neuroscience, 28:503-532, 2005.