Electrophysiology of Scorpion Peg Sensilla

Abstract

We describe a modification of an existing tip-recording technique 1,2 for electrophysiologically investigating short, peg-like sensory sensilla 3,4 . On the mid-ventral surface of all scorpions are two appendages called pectines, which have dense fields of mechano-and chemosensory peg sensilla 5,6 . One method for assessing chemoresponsiveness of these sensilla uses a tungsten electrode for extracellularly recording neural activity within a sensillum as a volatile odorant is introduced to the sensory field 5,7 . The limitations of this method include slow data collection and uncontrolled stimulant introduction to, and removal from, the peg field. To overcome these limitations, we developed a new tip-recording technique that uses nonpolar mineral oil as a medium through which to deliver water-based tastants to individual peg sensilla 8,9 . We have successfully applied this method to obtain sensillar chemoresponses to citric acid, ethanol, and salt. Here we describe the experimental protocol for such a study 9 . We think this new method may be useful for studying the response properties of other arthropod chemosensory systems, including those of insects 10, 11 and crustaceans 12. Video LinkThe video component of this article can be found at https://www.jove.com/video/2642/ Protocol 1. Pre-recording, Live Animal Preparation 1. Remove the scorpion from its home jar and place it in a pre-chilled glass container; next, place the jar containing the scorpion into a freezing environment (-5 °C) for a minimum of two minutes. This time may vary according to the age, size, species, etc. of the specific scorpion under study. But generally, the freezing environment phase is complete once the animal is motionless. 2. After two minutes, remove the immobilized scorpion from the cold glass container, and place it ventral side up on a microscope slide. Secure the stinger, tail, legs, and pedipalps with moldable clay (oil-based, Van Aken Plastalina). 3. Make a platform on which to put the scorpion's pectines. Adjust the platform's length and width according to the size of the pecten. Typically, our platforms are constructed out of microscope cover glass and are approximately 10(L) X 18(W) mm. 4. Adhere double-sided adhesive tape to the pecten platform, trimming the tape (if necessary) to fit. 5. To make a pectinal chamber, put three of the platform's four sides into pre-melted wax (we use 100% beeswax chips) to a depth of 3-4 mm.We melt the wax by placing the chips within a glass petri dish, located on a hot plate. Once the wax on the edges of the pectinal chamber is cooled to room temperature, this should create walls of wax about 1 mm high. 6. On the animal, locate the point of pectinal insertion, and place the un-waxed edge of the platform (tape side-up) just posterior to it. Afterward, stabilize the platform (so that it will not move later on) by gently pressing its right and left peripheral edges against the clay used to restrain the animal's legs. 7. Use fine-tipped forceps to carefully place the pecten or pectines in...

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

“…We feel confident that the signals we recorded emanated from neurons within the impaled sensillum. Pore-tip recordings using electrolyte-filled glass electrodes of pectines submerged in mineral oil show the same types of waveforms we saw in our recordings [5,24,25], which further corroborates that we were accessing neurons resident to the sensillum and not from neighboring sensilla. We saved the raw records using Spike2 software (Cambridge Electronics Design) and isolated the action potentials from background noise using the "New Wavemark" module.…”

“…In fact, the neural projection from peg sensilla is extensive, topographically arranged, and represents the largest input to the scorpion central nervous system [29][30][31][32]. Previous recordings from peg sensilla using a technique of recording from pectines submerged in mineral oil using electrolyte filled glass pipettes indicate that the neural responses of the A cells are largely similar among the peg population [5,24,25,33]. It seems possible that a simple, local feedback circuit helps prevent sensory adaptation [34] of the A cells.…”

Evidence of learning walks related to scorpion home burrow navigation

“…Our estimates of the pattern detection capacity of scorpion pectines are informed by electrophysiological studies showing that peg sensilla responded similarly to a variety of chemicals presented to the pore at the peg tip (Knowlton and Gaffin, 2009; 2010; 2011a;b; Gaffin and Walvoord, 2004). 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).…”

Evidence of learning walks related to scorpion home burrow navigation

“…This trade-off has been examined in various vision-based simulations ( Gaffin et al, 2015 ; Gaffin and Brayfield, 2016 ) and in a navigation simulation modeled on scorpion pectines ( Musaelian and Gaffin, 2020 preprint). Our estimates of the pattern detection capacity of scorpion pectines are informed by electrophysiological studies showing that peg sensilla responded similarly to a variety of chemicals presented to the pore at the peg tip ( Knowlton and Gaffin, 2009 , 2010 , 2011a , b ; Gaffin and Walvoord, 2004 ). 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 ).…”