When a cockroach is stung by a jewel wasp, the hapless victim is in for a deeply unpleasant experience. After the venom has robbed the cockroach of its free-will to walk, the wasp leads the victim back to a burrow to be colonised by its larva and consumed from the inside out. How the wasp's venom turns cockroaches into zombies has long intrigued Frederic Libersat. Knowing that the venom seems to alter the activity of neurones that release the neurotransmitter octopamine, Libersat and his colleagues at Ben-Gurion University of the Negev decided to see whether the venom incapacitates its victims by interfering with octopamine release(p. 4411).
First the team tested whether the venom targeted the octopamine system by seeing if they could restore cockroach free-will by administering octopamine agonists (mimics) to stung cockroaches. Injecting octopamine agonists into the insect's circulatory system, the team restored the insect's ability to roam free. Next, knowing that octopamine releasing neurones were directly connected to regions of the brain targeted by the wasp attack, the team decided to try to reverse the toxin's effects by injecting an octopamine agonist directly into the stung brain regions. Amazingly, the zombies recovered significantly when injected in the protocereberum, part of the central brain, but not when injected in the subesophageal ganglion.
By directly replacing octopamine with the octopamine agonist in the protocereberum, the team had mostly restored the cockroaches ability to walk independently. Libersat and his team suspect that `venom injection into the head ganglia selectively depresses the motivation to move by modifying the release of octopamine as a neuromodulator in restricted regions of the cockroach brain'.