Rustom et al (2004) found a new form of intercellular communication–tunneling nanotubes (TNTs). These are 50 to 200 nm in diameter and a length of several times that, and are used to transport organelles, as witnessed by enhanced green flourescent protein staining. When they treated cells with a substance to depolymerize F-actin, no TNTs were formed, suggesting that acting-driven cell protusions contribute to the mechanism behind their formation.
The original finding was done in neuroendocrine cells, and the potential complications this process could add to brain signalling are non-trivial. Indeed, Gousset et al (2009) recently found that certain prions can commandeer the TNT system to move from the lymphoid system where they enter, to the peripheral nervous system, and finally to the CNS, where they do their damage in the rare Cruetzfeldt-Jakob disease. The moral of the story is that the brain is complicated.
Rustom A et al. 2004 Nanotubular highways for intercellular organelle transport. Science 303:1007-10. doi:10.1126/science.1093133.
Gousset K et al. 2009 Prions hijack tunnelling nanotubes for intercellular spread. Nature Cell Biology, Article in Press. doi:10.1038/ncb1841.