Single Sensillum Recordings for Locust Palp Sensilla Basiconica

Summary

This paper describes a detailed and highly effective protocol for single sensillum recordings from the sensilla basiconica on the palps of insect mouthparts.

Abstract

The palps of locust mouthparts are considered to be conventional gustatory organs that play an important role in a locust's food selection, especially for the detection of non-volatile chemical cues through sensilla chaetica (previously named terminal sensilla or crested sensilla). There is now increasing evidence that these palps also have an olfactory function. An odorant receptor (LmigOR2) and an odorant-binding protein (LmigOBP1) have been localized in the neurons and accessory cells, respectively, in the sensilla basiconica of the palps. Single sensillum recording (SSR) is used for recording the responses of odorant receptor neurons, which is an effective method for screening active ligands on specific odorant receptors. SSR is used in functional studies of odorant receptors in palp sensilla. The structure of the sensilla basiconica located on the dome of the palps differs somewhat from the structure of those on the antennae. Therefore, when performing an SSR elicited by odorants, some specific advice may be helpful for obtaining optimum results. In this paper, a detailed and highly effective protocol for an SSR from insect palp sensilla basiconica is introduced.

Introduction

Animals have evolved a range of chemosensory organs that sense exogenous chemical cues. In insects, the most important chemosensory organs are the antennae and the palps. On these organs, several types of chemosensory hairs, called chemosensory sensilla, are innervated by chemosensory neurons (CSNs) within the hairs. CSNs in chemosensory sensilla recognize specific chemical cues through signal transduction from chemical stimuli to electrical potentials that are subsequently transferred up to the central nervous systems^1,2,3.

CSNs express various ch....

Protocol

1. Preparation of Instruments and Insect

1. Preparing tungsten electrodes and stimuli solutions
   1. Fix a new tungsten wire (diameter of 0.125 mm, length of 75 mm) into a micromanipulator and sharpen it in a 10% (w/v) sodium nitrite (NaNO₂) solution in a syringe at 10 V provided by a power supply for about 1 min under a stereomicroscope (40X magnification).
   2. Dip the sharpened tungsten wire repeatedly into the 10% NaNO₂ solution, about 4 mm at 5 V in < 1 min (Figure 1A).
   3. Examine the diameter of the sharpened tungsten tip frequently under the stereomicroscope u....

Results

Two sensilla subtypes (pb1 and pb2) on the locust maxillary palp are identified based on different response dynamics to chemical odorants (10% 1-nonanol and 10% nonanoic acid). The neurons in pb1 produce significantly more spikes to 1-nonanol than to nonanoic acid while the neurons in pb2 are significantly less activated by 1-nonanol compared with nonanoic acid (Figure 4). Hexanal and E-2-Hexenal can evoke a locust palp opening response (POR)

Discussion

Insects rely on palps to detect food odors, and their palps are believed to play an important role in speciation^13,27. The palps are simple olfactory organs and are receiving increasing attention as an attractive model for the exploration of the neuromolecular networks underlying chemosensation²⁸.

Insect labellar and palp SSRs have been successfully performed on Drosophila melanogaster, Anopheles ga.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Tungsten wire	ADVENT	W559504	Used for making the electrode and fixing the palp
NaNO2	Sigma-aldrich	563218-25G	Used for sharpening the tungsten wire
AC Power Supply	Syntech	A2-70	Providing the voltage in sharpening the tungsten wire
Stereoscope	Motic	SMZ-163	Used for observing the sharpening of tungsten wire
Microscope	Olympus	W-51	Used for observing the sensilla on locust maxillary palp
Intelligent Data Acquisition Controller	Syntech	IDAC-4	Real-time on screen display of all signals before and during recording
Stimulus controller	Syntech	CS-55	Used for controlling the stimulus application
Electronic micromanipulator	C.M.D.T	CFT-8301D	Used for minor movement of the recording electrode
Micromanipulator	Narishige	MN-151	Used for minor movement of the reference electrode
Speaker	EDIFIER	R101T06	Connected with IDAC-4 and providing sound for the signal
Magnetic base	PDOK	PD-101	Used to hold the electrode, and stimulus delivery tube
Vibration Isolation Table	TianHe	HAP-100-1208	Used for isolating the vibration from the equipment
Glass slide	CITOGLAS	ZBP-407	Used for making the base for the MPH
Blu-tack	Bostik	Blu-tack-45g	Fixing the tungsten wire
Pasteur tube	YARE	WITEG	Placing the filter paper containing stimuli stimulus solutions