ORIGINAL PAPER Synganglion histology in different stages of Rhipicephalus sanguineus ticks (Acari: Ixodidae) Gislaine Cristina Roma & Pablo Henrique Nunes & Rafael Neodini Remédio & Maria Izabel Camargo-Mathias Received: 17 October 2011 / Accepted: 13 December 2011 / Published online: 5 January 2012 # Springer-Verlag 2012 Abstract The present study performs a morpho-histological description of the central nervous system of Rhipicephalus sanguineus ticks in order to analyze if there are differences in this tissue among larvae, nymphs, and adults. The results showed that the central nervous system in all the life stages of R. sanguineus consists of a mass of fused nerves named synganglion. Externally, this organ does not present segmen- tation, consisting of a single structure located ventromedially in the third anterior of the body. This organ is externally covered by the neural lamella or neurilemma, a uniform and acellular layer. Below, there is the periganglionic membrane or perineurium, formed by glial cells, which are characterized by their elongated nuclei. The esophagus penetrates the syn- ganglion dividing it in two regions: supraesophageal, which is the smaller of the two and consists of a protocerebrum, a single dorsal ganglion located anteriordorsally to the esopha- gus; and the subesophageal, which is the largest part of the synganglion, located in the posterior region and ventral to the esophagus. Internally, the synganglion is subdivided in an external cortical region—which contains the cellular body of the nervous cells—and an internal neuropile formed by a set of neural fibers and it is constituted by bilaterally symmetric ganglia, from where nerves emerge towards several parts of the body. The results here obtained showed that there are no differences in the morpho-histology of this tissue in different life stages of R. sanguineus, suggesting that the initial struc- ture is maintained during the whole life cycle of the tick, i.e., from larval to adult stage. Introduction The tick Rhipicephalus sanguineus is originally from the African continent and is currently found in all countries of America, probably being the species of higher occurrence in the world (Paz et al. 2008). In Brazil, in the early twentieth century, this species presented a restricted distribution, being present only in some states (Aragão 1936); however, it is today present in all the Brazilian territory (Labruna 2004). The medical-veterinary importance of R. sanguineus lies in the fact of this ectoparasite is the main vector and reser- vatory of Ehrlichia canis, being also responsible for the transmission of other pathogens such as Babesia canis, Babesia caballi, and Babesia equi (Sexton et al. 1976), as well as Hepatozoon canis (Craig 1990). Some studies have also reported that R. sanguineus would be a potential vector agent of Leishmania chagasi, causative agent of canine visceral leishmaniasis (Coutinho et al. 2005), in addition to being considered a potential transmitter of rickettsial infec- tion, causative agent of Brazilian Spotted Fever for the human being (Dantas-Torres et al. 2006; Louly et al. 2006; Cunha et al. 2009; Ogrzewalska et al. 2010). G. C. Roma (*) : R. N. Remédio : M. I. Camargo-Mathias Departamento de Biologia, Instituto de Biociências, Universidade Estadual Paulista “Júlio de Mesquita Filho”, UNESP, Avenida 24 A, 1515, 13506-900 Rio Claro, São Paulo, Brazil e-mail: gislaineroma@yahoo.com.br P. H. Nunes Departamento de Medicina Veterinária Preventiva e Saúde Animal, Faculdade de Medicina Veterinária e Zootecnia, USP, Avenida Prof. Orlando Marques de Paiva, 87, 05508-270 São Paulo, SP, Brazil Parasitol Res (2012) 110:2455–2463 DOI 10.1007/s00436-011-2785-6