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lab.png Jewel Wasps (Ampulex compressa) are amazing creatures and their form of parental care has received quite some attention not only by scientists but also from the general media, and rightfully so. This parasitoid wasp serves for its young by hunting cockroaches as food. But it doesn't serve the cockroach to the offspring in pieces. No, it first performs brain surgery on the 'roaches to render them docile and then lays an egg onto the pacified animal from which a larva will hatch which then burrows into the cockroach to eat it from the inside, without any countermeasures of the cockroach. If you don't believe me, believe the History channel:

What does the wasp do to the cockroach brain to so pervasively change the way it works? Last week, Ram Gal and Frederic Libersat came a step closer to answering this question. They report in the journal PLoS One that The animal searches for specific brain regions with its stinger to inject its mind-altering venom. Insect brains have a hole in the middle, where the first part of its gut, the esophagus pases through. The part of the brain that is above the esophagus is called the supraesophageal ganglion and the part below is called the subesophageal ganglion. The researchers already knew that one target for venom injection was the supraesophageal ganglion from a previous study. For the new study, one of their experiments was to have wasps sting cockroaches in which the experimenters had removed the subesophageal ganglion. They found that the duration of the sting was extended to over three minutes, where usually it only lasts for less than 40 seconds. Maybe the wasp kept searching for the missing ganglion before it gave up?

To further test if indeed the subesophageal ganglion may be the target of venom injection, the researchers injected both Procaine, a local anesthetic and wasp venom which they had milked from the animals, into the cockroach subesophageal ganglion. The result was the same for cockroaches injected with venom or with Procaine: both substances, when injected into the subesophageal ganglion, rendered the 'roaches docile, greatly reducing their spontaneous and elicited walking distances. Moreover, the researchers recorded that neural activity in the subesophageal ganglion was greatly reduced in stung and Procain injected animals, compared to controls. Interestingly, injecting the substances into the supraesophageal ganglion did not have any dramatic effects, raising the question of why the animal stings there as well. The authors discuss this as follows:
The exact role of the SupEG in the venom-induced manipulation of the cockroach motor behavior remains, as yet, rather elusive. Several possibilities can be offered, such as a role in evoking the excessive grooming behavior seen in stung cockroaches [13], or importance for venom-induced changes in cockroach metabolism [11]. It is also possible that the SupEG, in concert with the SEG, plays a role in inducing certain aspects of venom-induced hypokinesia either directly, by affecting specific circuitries in this ganglion, or indirectly, by affecting ascending SEG interneurons which, in turn, modulate SupEG circuitries that control motor behavior. A direct effect of the venom on the SupEG apparently contradicts previous studies which showed that decerebrated insects (i.e., those without a SupEG) tend to walk uninhibitedly (see, for instance, [23], [24], [38][41]), suggesting a generally inhibitory effect of this ganglion on locomotion. However, it has also been shown that certain structures within the SupEG, and especially the Central Body Complex, affect some finer aspects of locomotion, including the frequency, duration and coordination of walking, turning behavior and obstacle climbing [19], [22], [23], [35], [42][46]. The venom could thus, in principle, specifically manipulate these SupEG structures, in addition to manipulating SEG activity, to further control the initiation of locomotory behavior in the cockroach prey.

Apart from the fascinating biology, this paper is interesting also from a more conceptual point of view. The authors do not shy away from using terms one may find controversial such as 'drive' and 'free will', e.g. in the first paragraph of their discussion:
Cockroaches stung by the parasitoid Jewel Wasp (A. compressa), although not paralyzed, loose the ability to self-initiate locomotion for several days [18]. This deficit cannot be attributed to an overall sleep-like state for three main reasons. First, the deficit is highly specific, in that the threshold for initiation of other motor behaviors (such as righting, swimming, flight, etc.) is little affected [10]. Second, stung cockroaches do not assume a typical ‘quiescent’ position [28] and occasionally move their antennae in an exploratory manner. Third, when startled by a supra-threshold stimulus, stung cockroaches respond by jumping in place but do not perform the stereotypic subsequent run [14]. Thus, and since the sensory and motor systems per se are fully functional in stung cockroaches [12], [14], the wasp venom appears to specifically decrease the cockroach's drive for walking. The fact that the wasp injects its neurotoxic venom directly into the cockroach's cerebral ganglia to ‘hijack the cockroach's free will’ allows us to explore the neuronal substrate responsible for this unique behavioral manipulation.

They also cite our study on spontaneous flight behavior and use the term 'rest state' which is something we are actively studying in our own experiments, ever since I read about Marcus Raichle's work on the default mode network in humans. Clearly, general brain organization is centered around the spontaneous activity of brains and how it is modulated by sensory stimuli. More and more researchers are realizing this fundamental aspect now. This, for a neurobiological study highly unusual model system provides yet one more piece of evidence that there is a pervasive and radical paradigm shift in the neurosciences in that the conceptual framework is moving away from brains as passive stimulus-response systems towards a view of brains as active organs which probe the environment by spontaneous actions and then evaluate its responses via sensory systems (brains as output/input devices).

Gal, R., & Libersat, F. (2010). A Wasp Manipulates Neuronal Activity in the Sub-Esophageal Ganglion to Decrease the Drive for Walking in Its Cockroach Prey PLoS ONE, 5 (4) DOI: 10.1371/journal.pone.0010019
Posted on Wednesday 14 April 2010 - 11:07:06 comment: 0

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