Endocannabinoids are fat-soluble chemicals used for local signaling, most notably retrograde signaling among neurons: they can send signals backwards. They're hydrophobic, diffusing well through cell membranes but not traveling well in water. This makes them useful for sending very short-distance signals.
http://en.wikipedia.org/wiki/Endocannabinoid_system
Endocannabinoids are fat-soluble chemicals used for local signaling, most notably retrograde signaling among neurons: they can send signals backwards. They're hydrophobic, diffusing well through cell membranes but not traveling well in water. This makes them useful for sending very short-distance signals.