Are mechanoreceptors involved in the neural circuitry of scorpion peg sensilla ?

Scorpion pectines are paired, ventral appendages that extend from their eleventh body segment. Each pecten resembles a comb with a jointed spine connecting numerous teeth. The ventral surface of each tooth contains a dense patch of truncated hairs, called peg sensilla. Morphological and electrophysiological studies have concluded that numerous chemoreceptive neurons are present in each peg while only one mechanoreceptor is present. Synaptic interactions between chemosensitive cells have been identified via cross-correlation analysis; however, the mechanoreceptor has received very little attention, and it is unknown if it is part of the peg circuitry. Our research focused on the general characteristics and roles of the mechanoreceptors in peg sensilla of the desert grassland scorpion (Paruroctonus utahensis). Extracellular electrophysiological recordings were obtained from the bases of individual pegs during mechanical stimulation. These recordings were then segregated into individual cellular firings using wave-form analysis, which showed the existence of four different waveforms (three chemoreceptors and one mechanoreceptor). Cross-correlation analysis did not reveal signs of synaptic interaction between the mechanoreceptor and two of the chemoreceptors while a third was inconclusive. Taken together with previous morphological studies it appears that the chemoreceptors and mechanoreceptors form synaptically isolated neural populations in scorpion peg sensilla.