[ihodes]

Here's the Nature paper if anyone's interested (from Dec 2010) http://www.nature.com/neuro/journal/v14/n2/full/nn.2728.html

We had known previously that the axons could send messenger proteins back to the soma (cell body), thus modulating transmitter productions, and could have an inhibitory or excitatory effect on the cell as a whole. We were also aware of axo-axonic synapses, whereby axons could inhibit other axons (among some other things).

EDIT: The above is just extremely brief background of well-known facts about axon messaging.