Different physiological roles of two dopamine receptors in salivation of the blacklegged tick, Ixodes scapularis Say

Ticks are obligatory ectoparasites of many vertebrates and transmit the pathogens that cause diseases including the Lyme disease, the most commonly reported vector-borne disease in the upper Midwest and Northeast of the United States.  Tick salivary secretion is crucial for successful feedings of ticks.  Ticks inject bioactive salivary components into the host to compromise the immune responses of the host and to remove excessive water and ions after the ingestion of large amount of blood meal.  Control of the salivary glands involves dopamine that is the most potent salivation inducer.  We has previously characterized two dopamine receptors expressed in the salivary glands of blacklegged tick (Ixodes scapularis Say) and named each as dopamine receptor (D1) and invertebrate-specific dopamine receptor (InDR) based on their sequence similarities to the vertebrate dopamine receptors.  We have identified receptor-specific antagonists and agonists by using functional expressions of the dopamine receptors in a mammalian cell line.  The pharmacological tools were also used for in vitro assays, monitoring the changes of volume in the salivary glands acini under microscope and measuring the amount of salivary secretion in isolated salivary glands.  We propose that D1 receptor activates fluid transport and InDR controls (or modulates) the activity of acinar valve. Understanding the mechanism of fluid secretion of tick salivary glands will lead us to the development of novel methods for disruption of tick feeding, thus allowing for the prevention of pathogen transmission.