The physiological events regulated by neuropeptide signaling via GPCR in different phases of tick blood feeding

Tick salivary secretion is known to be regulated by various neuropeptides and their receptors (G protein-coupled receptors, GPCRs) via the peptidergic axonal projection from the synganglion. During the slow phase (4-5 days after blood feeding) of tick blood feeding, two dopamine receptors, the dopamine receptor (D1) and the invertebrate specific D1-like dopamine receptor (InvD1L), orchestrate the dynamic response of type III acini for salivation, which is controlled by inward fluid transport and expulsion of primary saliva, respectively. However, the physiological role of other neuropeptides and GPCRs during tick feeding remains unclear. To investigate the physiological role of neuropeptides and GPCRs during different phases of tick blood-feeding, salivary glands were prepared from unfed, 3, 18, 60, and 96 h post blood feeding, as well as engorged Haemaphysalis longicornis to profile differentially expressed transcripts. The results showed high expression levels of the Bursicon receptor and Ast-B receptor in the salivary glands of engorged H. longicornis. The results suggest a link correlation between the degeneration of salivary glands and neuropeptide signaling. However, further studies, such as RNAi, are needed to clarify this relationship. Additionally, proteomic analysis may provide further insights into the physiological role of neuropeptides and GPCRs during tick feeding.