Submitted to: Experimental and Applied Acarology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/8/2007
Publication Date: 12/10/2007
Citation: Hummel, N.A., Li, A.Y., Witt, C.M. 2007. Serotonin-like immunoreactivity in the central nervous system of two Ixodid tick species. Experimental and Applied Acarology. 43(4):265-278. Interpretive Summary: Ticks are among the most significant vectors of human and animal disease causing organisms. Due to severe problems of resistance to all major classes of acaricides, fundamental study on the physiology and molecular biology of tick species is necessary in order to develop novel tick control and eradication technology. Serotonin is an important molecule that has been shown to play critical physiological roles in invertebrates. A study was conducted to determine if serotonin is present in the nervous system of the winter tick, Dermacentor albipictus and the lone star tick, Amblyomma americanum. We used the immunocytochemical techniques to detect the presence of serotonin in the synganglion (CNS) of unfed adult R. microplus. The results indicate serotonin is present in many cells in specific regions of the tick brain, suggesting that serotonin may be involved in the control and/or modulation of feeding behavior and in regulating locomotion. To our knowledge, this is the first report of the detection of serotonin in ticks using the immunocytochemical technique. The findings from this study advance our knowledge of tick physiology, and may help in the effort to identify novel targets for the development of new tick control technologies.
Technical Abstract: Immunocytochemistry was used to detect the presence of serotonin-like immunoreactive (5HT-IR) neurons and neuronal processes in the central nervous system (CNS), the synganglion, of two Ixodid tick species; the winter tick, Dermacentor albipictus and the lone star tick, Amblyomma americanum. Serotonin-like immunoreactive neurons were identified in the synganglion of both tick species. D. albipictus has a significantly higher number of 5HT-IR neurons than A. americanum. The number of 5HT-IR neurons is significantly different between sexes in D. albipictus but is not significantly different between sexes in A. americanum. 5HT-IR neurons that are located in the cortex of the synganglion project processes into various neuropils, invading neuromeres in the supraesophageal ganglion including the protocerebrum, postero-dorsal, antero-dorsal and cheliceral neuromeres. In the subesophageal ganglion, dense 5HT-IR neuronal processes are found in the olfactory lobes, pedal, and opisthosomal neuromeres. Double-labeling with neurobiotin backfilled from the first leg damaged at the Haller’s organ revealed serotoninergic neuronal processes surrounding the glomeruli in the olfactory lobe. The high number of the 5HT-IR neurons and the extensive neuronal processes present in various regions of the synganglion suggest that serotonin plays a significant role in tick physiology.