Synganglial Morphology and Neurosecretory Centers of Adult Amblyomma americanum (L.) (Acari: Ixodidae)

Abstract

Lone star ticks, Amblyomma americanum (L.), were processed by standard histological means for paraffin embedding, sectioning, and staining by the paraldehyde-fuchsin technique. The synganglion is highly condensed around the esophagus and possesses paired optic, cheliceral, palpal, pedal I-IV nerves, and opisthosomal nerves and a single unpaired esophageal nerve. Although optic nerves were observed leading from the eyes to the protocerebrum, distinct optic ganglia were not seen in any of the preparations examined. The paraldehyde-fuchsin technique revealed 14 neurosecretory centers (11 paired, 3 unpaired) within the synganglion, which are described in relation to the underlying neuropilar structure. A previously undescribed internal subesophageal center that consists of a single cell was observed within a cluster of perikarya lying posteriorly adjacent to the esophagus. A three-dimensional reconstruction of the internal neuropilar structure of the synganglion was made, and the included neurosecretory centers were mapped. Comparisons are made to previous work on other ticks, and physiological relationships are considered.

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

“…This study confirms that A. americanum olfactory sensilla project into olfactory lobes that, according to Prullage et al (1992) are paired structures containing numerous and dense clusters that reside beneath the ventral surface of the ventral neuropile pedal ganglia I and commissures connecting the pedals ganglia I and II. Further, the current work describes sensory neurons of the taste sensilla associated with the palpal organ of A. americanum that project into the palpal ganglion and do not extend to the olfactory lobes.…”

“…The general anatomical structures of the central nervous system have been described for several tick species (OBENCHAIN & OLIVER, 1976;MARZOUK et al, 1987;EL SHOURA, 1986;PRULLAGE et al, 1992;ROMA et al, 2012;SONENSHINE & ROE, 2014). In Argas persicus, the sensory projections of taste sensilla, located in the distal segment of the palp, extend to the subesophageal and palpal glanglia (SRIDHARAN et al, 1998).…”

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

“…The nervous system of the ticks, mainly adults, has been described by several authors (Obenchain and Oliver 1976;Roshdy and Marzouk 1984;Binnington 1986;El Shoura 1989;Sonenshine 1991;Oliver et al 1992;Prullage et al 1992); however, these descriptions were made a long time ago and need to be reviewed. In this sense, the present study performs a detailed morpho-histological description of this system in all life stages of R. sanguineus with the aim to fill the morphophysiological gaps left and analyze if there would be differences during the differentiation of this tissue.…”

“…This organ is ventrally located between the gnathosoma and the genital pore, approximately between the first and second pair of legs, being crossed by the esophagus, which divides it in two regions: (1) supraesophageal (anterior and dorsal to the esophagus) and (2) subesophageal (posterior and ventral to the esophagus) (Roshdy and Marzouk 1984;Sonenshine 1991;Prullage et al 1992). According to Severino et al (1984) and Sonenshine (1991), the structure of the nervous system of the ticks is similar between Argasidae and Ixodidae.…”

“…According to Sonenshine (1991), Oliver et al (1992) and Prullage et al (1992), the synganglion is externally covered by an acellular layer or neurilemma below which there is a periganglionic membrane or perineurium. Internally, this organ is divided in an external cortical region, which contains the bodies of nervous cells and an internal region known as neuropile, formed by the extension of nervous cells.…”