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 arborizations 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 glomeruli was not counted in males because they were 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.
Highlights
Global climate change is increasing the complexity of the problem with ticks and tick-borne diseases (PÉREZ DE LEÓN et al, 2012; DANTAS-TORRES, 2015; MOYER, 2015)
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
Summary
Global climate change is increasing the complexity of the problem with ticks and tick-borne diseases (PÉREZ DE LEÓN et al, 2012; DANTAS-TORRES, 2015; MOYER, 2015). Tick olfactory receptors reside mainly in the Haller’s organ that is located on the dorsal surface of tarsus I of both forelegs and these receptors detect volatile molecules (HAGGART & DAVIS, 1980; STEULLET & GUERIN, 1992; STEULLET & GNERIN, 1994a, b; LEONOVICH, 2004; SOARES & BORGES, 2012). Taste receptors are present in the distal segment of the palps and chelicerae, and the tip of tarsus I on the legs. These taste receptors detect non-volatile compounds (WALADDE & RICE, 1977; WALADDE, 1982; WALADDE & RICE, 1982; TAYLOR et al, 1991; GRENACHER et al, 2001; SOARES et al, 2013; FERREIRA et al, 2015). Ticks integrate the sensory information received by olfactory and taste receptors and transmit these to the synganglion, which is the tick’s central nervous system
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