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Title: Functional and Pharmacological Characterization of a Tyramine Receptor from the Southern Cattle Tick, Rhipicephalus microplus

item GROSS, AARON - Iowa State University
item KIMBER, MICHAEL - Iowa State University
item Temeyer, Kevin
item Li, Andrew
item Miller, Robert
item Perez De Leon, Adalberto - Beto
item COATS, JOEL - Iowa State University

Submitted to: Entomological Society of America Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/31/2013
Publication Date: N/A
Citation: N/A

Interpretive Summary: The southern cattle tick, Rhipicephalus (Boophilus) microplus, transmits the causative agents (Babesia spp) of cattle tick fever, a severe and frequently fatal disease of cattle. Although the southern cattle tick has been eradicated within the United States, it remains a continuing threat to the U.S. cattle industry because the tick is widespread in Mexico and other Latin American countries and has developed considerable resistance to several types of chemical acaricides used for tick control. Amitraz is one of the acaricides for which tick resistance has been reported in Mexico. Amitraz is believed to act by binding to octopamine receptors in the central nervous system of ticks. Previous research identified mutations in a presumptive octopamine receptor of amitraz-resistant ticks, however, the biochemical activity of this receptor and its potential involvement in resistance to amitraz was not demonstrated. We report new research to characterize this receptor biochemically and pharmacologically and its interaction with amitraz and related compounds to clarify the role of this receptor in tick resistance to amitraz.

Technical Abstract: The southern cattle tick, Rhipicephalus (Boophilus) microplus, vectors the causative agents (Babesia spp.) that result in cattle tick fever. The tick is a continuing threat to the United States, which currently maintains a permanent quarantine zone along the Texas-Mexico border. Detection of the southern cattle tick, inside or outside of this quarantine area, results in either chemical acaricide treatment or pasture vacation for several months. Recently, several tick populations resistant to various chemical acaricides have been detected in Mexico. This includes ticks that are resistant to amitraz, a formamidine insecticide, which is believed to work at octopamine receptors. Previously, a putative octopamine receptor was reported from susceptible and resistant populations of R. microplus. A two-site mutation has been observed in a G-protein-coupled receptor (GPCR), which preferentially responds to tyramine. However, characterization of this target as a potential resistance mechanism has not been investigated. Here we functionally and pharmacologically characterized this receptor. In addition, we characterized its interaction with formamidine parent compounds and metabolites.