Synaptic Interactions in Scorpion Peg Sensilla Appear to Maintain Chemosensory Neurons within Dynamic Firing Range

Abstract

Scorpions have elaborate chemo-tactile organs called pectines on their ventral mesosoma. The teeth of the comb-like pectines support thousands of minute projections called peg sensilla (a.k.a. “pegs”), each containing approximately 10 chemosensory neurons. Males use pectines to detect pheromones released by females, and both sexes apparently use pectines to find prey and navigate to home retreats. Electrophysiological recordings from pegs of Paruroctonus utahensis reveal three spontaneously active cells (A1, A2, and B), which appear to interact synaptically. We made long-term extracellular recordings from the bases of peg sensilla and used a combination of conditional cross-interval and conditional interspike-interval analyses to assess the temporal dynamics of the A and B spike trains. Like previous studies, we found that A cells are inhibited by B cells for tens of milliseconds. However, after normalizing our records, we also found clear evidence that the A cells excite the B cells. This simple local circuit appears to maintain the A cells in a dynamic firing range and may have important implications for tracking pheromonal trails and sensing substrate chemistry for navigation.

Mechanosensory pathways of scorpion pecten hair sensillae—Adjustment of body height and pecten position

“…Similar multisegmental pathways associated with mechanosensory sensillae on the body have been described previously in other scorpion species (Babu et al, 1993;Kasaiah et al, 1989;Palka & Babu, 1967). In conclusion, this pathway supports functionality of the fascinating pecten organs in the context of mating and navigation (Gaffin et al, 2021;Gaffin & Brownell, 1992;Gaffin & Brayfield, 2017;Krapf, 1986;Melville et al, 2003;Musaelian & Gaffin, 2020;Steinmetz et al, 2004).…”

“…Each peg sensilla consists of a firm shaft in which the dendrites of several chemosensory neurons communicate with the environment through a distally located slit opening, while the dendrite of one single mechanosensory neuron innervates the base of the shaft (Brownell, 1988(Brownell, , 1998Foelix & Müller-Vorholt, 1983;Gaffin & Brayfield, 2017;Gaffin & Shakir, 2021;Hughes & Gaffin, 2019;Melville, 2000;Wolf, 2008Wolf, , 2017.…”

“…The ventral surfaces of the pecten teeth are studded with bimodal peg sensillae (Figure 2), resulting in a large area for sensillae presentation and allowing a high sensitivity for chemical and textural cues. Each peg sensilla consists of a firm shaft in which the dendrites of several chemosensory neurons communicate with the environment through a distally located slit opening, while the dendrite of one single mechanosensory neuron innervates the base of the shaft (Brownell, 1988, 1998; Foelix & Müller‐Vorholt, 1983; Gaffin & Brayfield, 2017; Gaffin & Shakir, 2021; Hughes & Gaffin, 2019; Melville, 2000; Wolf, 2008, 2017).…”

Evidence of learning walks related to scorpion home burrow navigation

“…Based on these data, it has been estimated that the pectines can conservatively detect from 10 12 to 10 40 different patterns ( Gaffin and Brayfield, 2017 ). Further, neurons in peg sensilla interact synaptically ( Gaffin and Brownell, 1997a ; Foelix and Müller-Vorholt, 1983 ; Melville, 2000 ; Gaffin, 2002 ), which appears to reduce sensory adaptation through a local feedback loop and may improve information fidelity for navigation ( Gaffin and Shakir, 2021 ).…”

Scorpion envenomation in Brazil: Current scenario and perspectives for containing an increasing health problem

“…However, very little is known about scorpions pherormone communication to make use of this approach. Nevertheless, the presence of pectens, sophisticated chemotactile organs in scorpions, points that this could be an important field of study that can be addressed for controlling scorpions’ infestation [ 146 ].…”