Neuronal projections from the Haller's organ and palp sensilla to the synganglion of Amblyomma americanum

Authors: BORGES, LIGIA - Brazil University; Li, Andrew; Olafson, Pia; RENTHAL, ROBERT - University Of Texas At San Antonio; Bauchan, Gary; Lohmeyer, Kimberly - Kim; Perez De Leon, Adalberto - Beto

Submitted to: Revista Brasileira de Parasitologia Veterinaria
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2016
Publication Date: 6/14/2016
Citation: Borges, L.M., Li, A.Y., Olafson, P.U., Renthal, R., Bauchan, G.R., Lohmeyer, K.H., Perez De Leon, A.A. 2016. Neuronal projections from the Haller's organ and palp sensilla to the synganglion of Amblyomma americanum. Revista Brasileira de Parasitologia Veterinaria. 25(2):217-224.

Interpretive Summary: The lone star tick is an important vector of pathogens that cause diseases affecting humans, livestock, and wildlife, including ehrlichiosis, tularemia, and Southern tick-associated rash illness. The bite of this tick species can also cause a person to develop allergy to red meat and meat products. Proper use of chemical repellents, such as DEET, can prevent tick bite and reduce the risk of disease transmission to humans. Ticks use carbon dioxide, body odors, and other chemical cures to find hosts and initiate blood feeding. Understanding host seeking behavior of ticks and the underlying physiological mechanisms would help develop novel repellent and antifeedant compounds to prevent tick bite. We conducted a study to investigate properties of receptor neurons associated with ticks’ sensory organs that are known to play a critical role in host detection. We labeled sensory neurons with a fluorescent dye, and used a confocal laser scanning microscope to visualize sensory neuron projections in tick’s central nervous system. The finding of distinct projections patterns of sensory neurons from the olfactory receptors and taste receptors indicates different information processing mechanisms are involved. Results from this study would aid discovery researches for specific chemicals that can either repel ticks or prevent ticks from biting people after they get on a person. The work is of interest to biologists, chemists, tick researchers, and chemical companies that develop new tick repellents.

Technical Abstract: The present study was conducted to elucidate the neuronal pathways between peripheral olfactory and taste sensilla and the synganglion in an Ixodidae tick species. The tarsus of the front legs (olfactory nerves) and the fourth palpal segment (gustatory nerves) of unfed Amblyomma americanum males and females were excised. A neuronal tracer, dextran tetramethylrhodamine, was used for filling of the sensory neurons. The synganglion preparations were examined using a confocal microscope. Neuronal barbarizations from the Haller’s organ were confined to the olfactory lobes and the first pedal ganglion. The estimated number of olfactory glomeruli ranged from 16 to 22 per olfactory lobe in the females. The number of glomeruliwas not counted in males because they were too densely packed. Sensory neurons associated with sensilla at the distal end of the palpal organ projected into the palpal ganglion in the synganglion through the palpal nerve. Gustatory sensory neurons associated with palpal sensilla projected into a commissure with several bulges, which are confined in the palpal ganglion. The findings of distinct projection patterns of sensory neurons associated with the Haller’s organ and palpal organ in the lone star tick from this study advanced our knowledge on mechanisms of sensory information processing in ticks.