Neural control of salivary glands in ixodid ticks

Abstract

Studies of tick salivary glands (SGs) and their components have produced a number of interesting discoveries over the last four decades. However, the precise neural and physiological mechanisms controlling SG secretion remain enigmatic. Major studies of SG control have identified and characterized many pharmacological and biological compounds that activate salivary secretion, including dopamine (DA), octopamine, γ-aminobutyric acid (GABA), ergot alkaloids, pilocarpine (PC), and their pharmacological relatives. Specifically, DA has shown the most robust activities in various tick species, and its effect on downstream actions in the SGs has been extensively studied. Our recent work on a SG dopamine receptor has aided new interpretations of previous pharmacological studies and provided new concepts for SG control mechanisms. Furthermore, our recent immunohistochemical studies have suggested that multiple neuropeptides are involved in SG control. Myoinhibitory peptide (MIP) and SIFamide have been identified in the neural projections reaching the basal cells of acini type II and III. Pigment-dispersing factor (PDF)-immunoreactive neural projections reach type II acini, and RFamide- and tachykinin-immunoreactive projections reach the SG ducts, but the chemical nature of these immunoreactive materials are unidentified yet. Here, we briefly review previous pharmacological studies and provide a revised summary of SG control mechanisms in ticks.

The Essential Role of Tick Salivary Glands and Saliva in Tick Feeding and Pathogen Transmission

“…In particular, two neuropeptides, myoinhibitory peptide (MIP) and SIFamide, have been found to be co-expressed in the pair of giant neurons in the synganglion whose axonal projections reach the basal regions of type II and III acini (Šimo et al, 2009a,b, 2011, 2012, 2013, 2014a). The SIFamide receptor, as evidenced by immunostaining, was found in proximity to the acinar valve (basal region of acini), suggesting its role in control of this structure (Šimo et al, 2009b, 2013).…”

Receptors for the neuropeptides, myoinhibitory peptide and SIFamide, in control of the salivary glands of the blacklegged tick Ixodes scapularis

“…Aminergic and peptidergic neuronal cells were characterized by immunohistochemistry (IHC) (Hummel et al, 2007; Šimo et al, 2009a; 2009b; 2011b). Our previous study utilized 15 different antibodies, which were originally raised against neuropeptides in many different species of insects and crustaceans, and found that the synganglion was rich in neuropeptides (Šimo et al, 2009a); these findings were confirmed by a peptidomic analysis (Neupert et al, 2009), as well as an analysis of homology-based neuropeptide gene prediction (Christie, 2008; Šimo and Park, unpublished data).…”

Structural characterization and modeling of the Borrelia burgdorferi hybrid histidine kinase Hk1 periplasmic sensor: A system for sensing small molecules associated with tick feeding

“…One provocative possibility is that one or more of Hk1's PBPs bind neurotransmitters, which are derived from amino acids and would be released by the host in response to tissue injury (i.e., formation of the feeding lesion) (Askenase et al, 1995; Dai et al, 2010; Theoharides et al, 2012). Tick saliva also contains a plethora of bioactive molecules, including dopamine and dopamine sulfate (Koci et al, 2014; Simo et al, 2012; Simo et al, 2011; Yalcin et al, 2010). Interestingly, using qRT-PCR, we recently reported significantly greater induction of c-di-GMP-dependent genes by B. burgdorferi in feeding nymphs compared to larvae (Caimano et al, 2015).…”