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Representative Results






Multi-unit Recording Methods to Characterize Neural Activity in the Locust (Schistocerca Americana) Olfactory Circuits

Published: January 25th, 2013



1Department of Biomedical Engineering, Washington University in St. Louis

We demonstrate variations of the extracellular multi-unit recording technique to characterize odor-evoked responses in the first three stages of the invertebrate olfactory pathway. These techniques can easily be adapted to examine ensemble activity in other neural systems as well.

Detection and interpretation of olfactory cues are critical for the survival of many organisms. Remarkably, species across phyla have strikingly similar olfactory systems suggesting that the biological approach to chemical sensing has been optimized over evolutionary time1. In the insect olfactory system, odorants are transduced by olfactory receptor neurons (ORN) in the antenna, which convert chemical stimuli into trains of action potentials. Sensory input from the ORNs is then relayed to the antennal lobe (AL; a structure analogous to the vertebrate olfactory bulb). In the AL, neural representations for odors take the form of spatiotemporal firing patterns distributed across ensembles of principal neurons (PNs; also referred to as projection neurons)2,3. The AL output is subsequently processed by Kenyon cells (KCs) in the downstream mushroom body (MB), a structure associated with olfactory memory and learning4,5. Here, we present electrophysiological recording techniques to monitor odor-evoked neural responses in these olfactory circuits.

First, we present a single sensillum recording method to study odor-evoked responses at the level of populations of ORNs6,7. We discuss the use of saline filled sharpened glass pipettes as electrodes to extracellularly monitor ORN responses. Next, we present a method to extracellularly monitor PN responses using a commercial 16-channel electrode3. A similar approach using a custom-made 8-channel twisted wire tetrode is demonstrated for Kenyon cell recordings8. We provide details of our experimental setup and present representative recording traces for each of these techniques.

1. Odor Preparation and Delivery

  1. Dilute odor solutions in mineral oil by volume to achieve the desired concentration level. Store a 20 ml mixture of mineral oil and the odorant in a 60 ml glass bottle. Insert two syringe needles into a rubber stopper (gauge 19), one from the bottom and the other from the top, to provide an inlet and an outlet line. Seal the glass bottle with this rubber stopper and attach a custom designed activated carbon filter to the inlet line (Figure 1A).
  2. The c.......

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Odor-evoked responses of a single ORN to two different alcohols are shown in the Figure 3D. Depending on the recording location (sensilla type, placement of the electrode) multi-unit recordings can be achieved.

A raw extracellular waveform from an AL recording is shown in Figure 6A. Action potentials or spikes of varying amplitudes originating from different PNs can be observed in this voltage trace. Although the locust antennal lobe has excitatory projection .......

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Most sensory stimuli evoke combinatorial responses that are distributed across ensembles of neurons. Hence, simultaneous monitoring of multi-neuron activity is necessary to understand how stimulus-specific information is represented and processed by neural circuits in the brain. Here, we have demonstrated extracellular multi-unit recording techniques to characterize odor-evoked responses at the first three processing centers along the insect olfactory pathway. We note that the techniques presented here have been used in .......

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The authors would like to thank the following for funding this work: generous start-up funds from the Department of Biomedical Engineering in Washington University, a McDonnell Center for Systems Neuroscience grant, a Office of Naval Research grant (Grant#: N000141210089) to B.R.


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Name Company Catalog Number Comments
Name Company Catalog Number Comments
      Electrophysiology Equipment
A.C. amplifier GRASS Model P55 for single sensillum recordings
Audio monitor (model 3300) A-M Systems 940000  
Custom-made 16 channel pre-amplifier and amplifier Cal. Tech. Biology Electronics Shop   for AL and MB recordings
Data acquisition unit National Instruments BNC-2090  
Fiber optic light WPI SI-72-8  
Light source 115 V WPI NOVA  
Manual micromanipulator WPI M3301R for locust brain recordings
Stereomicroscope1 on boom stand Leica M80 for locust brain recordings
Stereomicroscope2 Leica M205C for single sensillum recordings
Vibration-isolation table TMC 63-500 series  
Motorized micromanipulator Sutter Instruments MP285/T  
Oscilloscope Tektronix TD2014B  
      Electrodes/Construction Tools
16-channel electrode NeuroNexus A2x2-tet-3mm-150-121 for antennal lobe recordings
Borosilicate capillary tubes with filament, ID 0.69 mm Sutter Instruments BF120-69-10 for making glass electrodes
Micropipette puller Sutter Instruments P-1000  
Function generator Multimeter Warehouse SG1639A for gold-plating electrodes
Gold plating solution (non cyanide) SIFCO Industries NC SPS 5355  
Impedance tester BAK Electronics Inc. IMP-2 for gold-plating electrodes
Switch rotary Electroswitch C7D0123N for gold-plating electrodes
Pulse isolator WPI A365 for gold-plating electrodes
Q series electrode holder Warner Instruments 64-1091  
Silver wire 0.010" diameter A-M Systems 782500 ground electrode
8 pin DIP IC socket Digikey ED90032-ND  
Borosilicate capillary tubes with filament, ID 0.58 mm Warner Instruments 64-0787 twisted wire tetrode construction
Heat gun Weller 6966C  
Rediohm-800 wire Kanthal Precision Technologies PF002005  
Titer plate shaker Thermo Scientific 4625Q twisting wires
Carbide scissors, 4.5" Biomedical Research Instr 25-1000 for cutting twisted tetrode wires
Fine point tweezers HECO 91-EF5-SA for teasing tetrode wires apart
      Odor Delivery
6 ml syringe Kendall 1180600777 for custom designed activated carbon filter
Brown odor bottles Fisher 08-912-165  
Charcoal GAC-48C  
Desiccant Drierite 23005  
Drierite gas drying jar Fischer Scientific 09-204  
Heat shrink tubing 3M EPS-200 odor filter preparation
Hypodermic needle aluminum hub, gauge 19 Kendall 8881-200136 for providing inlet and outlet lines for odor bottles
Mineral oil Mallinckrodt Chemicals 6357-04 for odor dilution
Nalgene plastic tubing, 890 FEP Thermo Scientific 8050-0310 for carrier gas delivery
Pneumatic picopump WPI sys-pv820 for odor delivery
Polyethylene tubing ID 0.86 mm Intramedic 427421 for odor bottle outlet connections and saline profusion tubing
Stoppers Lab Pure 97041 for sealing odor bottles
Time tape PDC T-534-RP  
Tubing luer Cole-Parmer 30600-66  
Vacuum tube McMaster-Carr 5488K66  
100 x 15 mm petri dish VWR International 89000-304  
18 AWG copper stranded wire Lapp Kabel 4510013 wire insulation is used as rubber gaskets
22 AWG stranded hookup wire AlphaWire 1551 brain platform
Batik wax Jacquard 7946000  
Dental periphery Wax Henry-Schein Dental 6652151  
Electrowaxer Almore International 66000  
Epoxy, 5 min Permatex 84101  
Hypodermic needle aluminum hub Kendall 8881-200136  
Protease from Streptomyces griseus Sigma-Aldrich P5147 for desheathing locust brain
Suture thread non-sterile Fisher NC9087024 for tying the abdomen after gut removal
Vetbond 3M 1469SB for sealing amputation sites
Dumont #1 forceps (coarse) WPI 500335  
Dumont #5 titanium forceps (fine) WPI 14096  
Dumont #5SF forceps (super-fine) WPI 500085 desheathing locust brain
10 cm dissecting scissors WPI 14393 for removing legs and wings
Vannas scissors (fine) WPI 500086 for removing cuticle, cutting the foregut
      Saline Profusion
Extension set with rate flow regulator Moore Medical 69136 for regulating saline flow
IV administration set with Y injection site Moore Medical 73190 for regulating saline flow

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