Regulation of tick attachment and rapid blood feeding through the dopamine receptors of the Asian longhorned tick, Haemaphysalis longicornis

The salivary secretion of ixodid ticks is regulated by several neuropeptides or neurotransmitters that interact with their receptor, G protein-coupled receptors (GPCRs). The orchestration of dopamine receptor (D1) and invertebrate specific D1-like dopamine receptor (InvD1L) is known to precisely control tick salivary secretion via the collection of primary saliva in the lumen and the expulsion of collected saliva, respectively. The two dopamine receptors (Haelo-D1 and Haelo-InvD1L) of Haemaphysalis longicornis were identified as 1278 bp (426 aa) and 1362 bp (454 aa) in length, respectively. Transcripts of D1 and InvD1L were profiled from the synganglion and salivary glands of female ticks at different stages of feeding (unfed, 3, 18, 60, 96 hours post-blood meal, and replete). Haelo-D1 and Haelo-InvD1L were significantly up-regulated during the early stage of blood-feeding in female ticks. Knockdown of Haelo-D1 and Haelo-InvD1L resulted in a significant reduction in dopamine-mediated salivation in partially fed female ticks, as well as a prolonged host-attachment period of unfed females of up to 53 hours. Additionally, the entire blood-feeding, from tick attachment to detachment, process was delayed by up to about 3 days by knockdown of Haelo-D1 and Haelo-InvD1L. In contrast to the period of tick blood-feeding, fully engorged RNAi ticks weighed 77mg to 120mg less after blood-feeding compared to control ticks. These results suggest that dopamine-mediated salivary secretion controls host-attachment in the early stage of tick blood-feeding, while regulating the amount of ingested blood in the rapid stage of tick blood-feeding.