Tick neurobiology: recent advances and the post-genomic era

Abstract

Increasing worldwide resistance to acaricides necessitates greater research on the identification of potential acaricide targets in ticks to aid in the control of these serious pests of medical and veterinary importance. Historically, and most likely in the future, acaricide targets are largely of neural origin, but our knowledge of tick neurobiology is surprisingly limited. The tick central nervous system is a fused nerve mass, termed the synganglion. Tick synganglion material is relatively easily accessible to most researchers and employing modern amplification methods of complementary-DNA construction is readily amenable for gene cloning investigations. The various tick neurotransmitter systems are described with emphasis on our current knowledge of both existing and potential acaricide targets at the molecular level. We describe the impact of mass gene sequencing (expressed sequence tag and genome projects), advances in bioinformatics and RNA-interference on target identification and validation.

Synganglion histology in different stages of Rhipicephalus sanguineus ticks (Acari: Ixodidae)

“…These data corroborate findings by Binnington and Obenchain (1982), Roshdy and Marzouk (1984), Binnington (1986), El Shoura (1989, Sonenshine (1991), Prullage et al (1992), and Lees and Bowman (2007) for other species of ticks.…”

“…According to Sonenshine (1991), peripheral nerves emerge from these ganglia, being responsible for the innervation of the appendixes, muscles, sensorial structures, tegument in addition to several internal organs. Several ganglia were found in the neuropile region of the individuals here analyzed, corroborating findings by other authors for other species of ticks (Roshdy and Marzouk 1984;Lees and Bowman 2007). According to Sonenshine (1991), optical, cheliceral, and palpal ganglia would be found in the supraesophageal region, while in the subesophageal region, the pedal, olfactory, and opisthosomal ganglia would be found.…”

“…from larval to adult stage, not presenting morphological changes during the differentiation of this tissue. In addition, no differences were observed in the morphology of the nervous tissue between unfed and fed ticks, corroborating data by Lees and Bowman (2007) for other species of ticks.…”

“…According to Coons and Alberti (1999) and Lees and Bowman (2007), this location allows the synganglion to be constantly supplied by hemolymph, which would allow the absorption and/or secretion of certain substances directly in the hemolymph. According to Battsetseg et al (2009), the synganglion of ticks are also responsible for the synthesis of kynurenine aminotransferase (KAT) molecule, an enzyme involved in tryptophan catabolism.…”

Increased expression of ATG genes during nonfeeding periods in the tickHaemaphysalis longicornis

“…Most hard tick species have a life span of several years in nature and of six to seven months under standardized laboratory conditions. 2,3 Nevertheless, ticks feed only three times in a lifetime: After hatching from an egg, the tick feeds initially as a larva, then as a nymph, and finally as an adult. The adult tick dies soon after oviposition.…”