Wireless Electrophysiological Recording of Neurons by Movable Tetrodes in Freely Swimming Fish

Summary

A novel wireless technique for recording extracellular neural signals from the brain of freely swimming goldfish is presented. The recording device is composed of two tetrodes, a microdrive, a neural data logger, and a waterproof case. All parts are custom-made except for the data logger and its connector.

Abstract

The neural mechanisms governing fish behavior remain mostly unknown, although fish constitute the majority of all vertebrates. The ability to record brain activity from freely moving fish would advance research on the neural basis of fish behavior considerably. Moreover, precise control of the recording location in the brain is critical to studying coordinated neural activity across regions in fish brain. Here, we present a technique that records wirelessly from the brain of freely swimming fish while controlling for the depth of the recording location. The system is based on a neural logger associated with a novel water-compatible implant that can adjust the recording location by microdrive-controlled tetrodes. The capabilities of the system are illustrated through recordings from the telencephalon of goldfish.

Introduction

Fish are the largest and most diverse group of vertebrates, and like other vertebrates they exhibit complex cognitive abilities such as navigating, socializing, sleeping, hunting, etc. Nevertheless, the neural mechanisms governing fish behavior remain for the most part unknown.

In the past few decades, extracellular recordings from immobilized fish have primarily been implemented to investigate different aspects of the neural basis of behavior^1,2. Although this technique is appropriate for some sensory systems, investigation of the full spectrum of the neural basis of behavior is di....

Protocol

All surgery procedures must be approved by the local ethics committees on animal welfare (e.g., IACUC).

1. Construction of the Microdrive Housing

1. To construct the housing, cut a 1 mm wide brass plate into a 19 mm x 29 mm x 1 mm plate using a saw. Cut two 5.5 mm slits on each of the long sides perpendicular to the edge, such that each slit is 6.5 mm away from the narrow sides (Figure 2A).
2. Using pliers, fold the area between the slits on the long sides inward, then fold the bottom part inward and the upper side outward to obtain the housing (Figure 2

Results

During a recording session the goldfish swam freely in a square water tank while the neural activity in its telencephalon was recorded. The goal of these experiments was to study how the neural activity of single cells determines the fish's behavior. To do so, spiking activity needed to be identified in the recorded data. The brain activity, while being recorded, was digitized at 31,250 Hz and high-pass filtered at 300 Hz by the data logger. Then, offline, a band-pass filter (300ͨ.......

Discussion

This protocol details the steps involved in implanting a tetrode array into the telencephalon of freely swimming goldfish. This technique implements a neural logger that amplifies and records the signals acquired from up to 16 channels along with a microdrive that can adjust the tetrode position in the brain. The microdrive makes it possible to adjust the position in the brain to optimize the recording.

This protocol can easily be modified for recording from other brain regions (see Vinepinsky.......

Materials

Name	Company	Catalog Number	Comments
0.7 mm round drill bits			Compatible with the drill.
15-blade Scalpel	Sigma-Aldrich
16 channel PCB board	Neurlynx	EIB-16
1X3M phillips flat head screws			Stainless steel. Any type.
1X3M phillips round head screws			Stainless steel. Any type.
27 cm X 19 cm X 1 mm brass plate			See Figure 2
2X6M phillips flat head screws			Stainless steel. Any type.
3140 RTV coating	Dow Crowning	2767996
75 µm Silver wire	A-M Systems
Brass machine screws #00-90		947-1006
Brass plates 7.5mm X 2.5mm X 0.6mm			A 3D drawing is provided. See supplementary 1
Coated Tungsten wire 25µm	California Fine Wire Company	5000160	Depending on the appication the tetrodes can be fabricated from any type of wire. Popular wires are nicrome wires that can be found with lower diameters (eg. A-M systems, 762000)
Coated Tungsten wire 50µm	A-M Systems	795500	Can be replaced with any other wire with low impedance
Cyanoacrilic glue
Dental Burnisher	ComDent UK		Any small sterille stainless-still tool will do.
Dental cement - GCFujiPLUS	GC	431011	Other dental cements would probably will work as well although we have never tried any other.
Dental drill or nail polish drill			Dental drills are expensive, a nail polish drill can be a cheap replacement.
Drill bit #65		947-65
Fast curing epoxy			Any 5 minutes curing epoxy can be used here.
Logger box with O-ring sealing			A 3D drawing is provided. See supplementary 1-3. The box should be machine fabricated (do not use 3D printers). Use transperant material, to be able to see the indicator LEDs on the logger.
Motorized turning device			Custom made as described in "open ephys" website. Can also be purchusaed from neurolynx ("Tetrode Spinner 2.0") or bulit by other means.
Mouselog-16 Neural logger	Deuteron Technologies Ltd		There are several neural loggers available on the market, including: SpikeGadget (UH32 32channels) and Neurologger 2/2A/2B of Alexei Vyssotski. It should be noted that weight is not a major contraint since it can be counterbalanced with floating Styrofoam
MS-222	Sigma Aldrich	E10521	Ethtl 3-aminobenzoate methanesulfonate 98%
Nano-Z plating	White Matter LLC		The nano-Z can be bought from several supllieres. Any impedance meter can be used, e.g. IMP-1 / 6662 / 2788, BAK Electronics.
PCB pins	Neurlynx	Neuralynx EIB Pins
Polymide tubing 250µm	A-M Systems	822000
Rechargable battery			3.7 Lipo battery, 370 mAh. Holds about 6 hours of recording. Smaller or larger battries can be used to reduce the weight or extend recording time.
Silicone tubing 0.64 mm	A-M Systems	806100
Stainless steel 1.5 mm	A-M Systems	846000
Sudium Bicarbonate	Sigma Aldrich	S9625
Tap #00-90		947-1301
Vaseline			Any type of soft petroleum skin protectant can be used here.