The Role of Biogenic Amines and Dopamine Receptors in Envenomation by the Parasitoid Wasp Ampulex compressa
The parasitoid wasp Ampulex compressa uses a unique biochemical strategy to exploit the American cockroach Periplaneta americana as a food source for its offspring. The wasp injects venom directly into the brain and subesophageal ganglion of the cockroach, which leads to a bout of grooming which lasts approximately 30 minutes. The cockroach subsequently falls into a state of hypokinesia, which is characterized by reduction of escape responses and inability to generate spontaneous movements. We investigated potential mechanisms of action for these venom-induced behaviors, focusing predominantly on the possible roles of the biogenic amine dopamine. Reserpine injection produces similar behavioral phenotypes to stung cockroaches by depleting presynaptic stores of biogenic amines. We determined that levels of dopamine, serotonin, octopamine, or tyramine in the head and thoracic ganglia were not depressed in stung cockroaches, but were dramatically reduced in reserpinized animals. We also investigated the effects of Ampulex venom and two major venom peptides (DG2847 and DG2807) on dopamine receptors in relation to sting-induced grooming and hypokinesia induction. The full-length cDNA encoding the D2-like dopamine receptor from Periplaneta americana (PeaD2R) was sequenced and cloned into a vector for expression in Chinese Hamster Ovary (CHO-K1) cells. Three dopamine receptors from Drosophila melanogaster (dDA1, DAMB, and D2R) were also cloned. Using an aequorin-based cell luminescence assay, pharmacological profiles were generated for each receptor using various synthetic dopamine receptor agonists and antagonists in order to determine the specificity of these compounds on each receptor subtype. The D2-selective compound sulpiride, when preinjected into cockroach hemolymph, significantly reduced sting-induced grooming. Dopamine, a neurotransmitter that has been implicated in sting-induced grooming, was determined to be present in milked venom by high performance liquid chromatography with electrochemical detection. We also investigated functional properties of Ampulex venom and venom peptides. We determined that neither Ampulex venom, nor the venom peptides, possessed antimicrobial activity, or induced cell death in vitro. Milked venom and the venom peptides induced a decrease in ligand-induced luminescence when incubated with CHO-K1 cells. This suggests that calcium mobilization is being altered when exposed to venom, which may disrupt signaling pathways in the central nervous system.