Chronic Recording of Extracellular Neuronal Activity in Behaving Animals

Ronald Szymusiak1, Douglas Nitz2

1 University of California, Los Angeles, California, 2 Neurosciences Institute, La Jolla, California
Publication Name:  Current Protocols in Neuroscience
Unit Number:  Unit 6.16
DOI:  10.1002/0471142301.ns0616s21
Online Posting Date:  February, 2003
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Two methods for recording extracellular neuronal activity in unanesthetized, unrestrained rats are described in this unit. Both use chronically‐implanted bundles of fine microwires to record electrophysiological activity. One method provides recordings of single and/or multiple unit activity from individual wires in a bundle (monotrode). Discrimination of individual neuronal potentials is based on action potential amplitude, or on a combination of action potential amplitude and shape. The second method uses a 2‐ to 4‐microwire array (stereotrode‐tetrode) to yield multiple unit recordings. Discrimination of individual neuronal potentials is based on action potential shapes and the relative amplitude of action potentials recorded simultaneously on the different wires in the array. These methods can provide stable, long‐term recording of neuronal activity during a variety of behavioral paradigms.

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Table of Contents

  • Strategic Planning
  • Basic Protocol 1: Surgical Implantation of Microwire Bundles and Data Acquisition in Rats
  • Support Protocol 1: Preparation of Microwire/Microdrives
  • Support Protocol 2: Analyses for Single‐ and Multiple‐Unit Recording Data
  • Basic Protocol 2: Surgical Implantation of Stereotrodes/Tetrodes and Data Acquisition in Rats
  • Support Protocol 3: Fabrication of Stereotrodes/Tetrodes
  • Support Protocol 4: Single‐Unit Wave Form Discrimination or “Cluster Cutting” for Stereotrode/Tetrode Recordings
  • Commentary
  • Figures
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Basic Protocol 1: Surgical Implantation of Microwire Bundles and Data Acquisition in Rats

  • Rats (Sprague‐Dauley, male or female, 250 to 350 g; Charles River)
  • Anesthetic (ketamine/xylazine; 80:10 mg/kg)
  • Alcohol swabs
  • Dental acrylic and solvent (methylmethacrylate; Co‐Oral‐Ite Dental)
  • Miniature electrical connector with 4 to 7 contacts
  • Solder (“44” Kester Solder)
  • Rat stereotaxic frame
  • Scalpel
  • Microdrives (see protocol 2)
  • Small machine screws for anchoring dental acrylic to skull (00 × ⅛‐in.; Morris Precision Screws & Parts)
  • Moto‐tool and grinding disk (Dremel)
  • Disposable 24‐G syringe needle
  • Stainless steel cannula (24‐G and 21‐G; ThinWall)
  • Microwires (see protocol 2)
  • Polyethylene tubing (0.023‐in. i.d. and 0.038‐in o.d.)
  • 3‐ml syringes
  • Low‐noise wire for recording cables (Filotex; Etude 22595, Alcatel)
  • Low‐noise electrical switching device, any type (e.g., rotary, sliding, patch panel)
  • Electrically shielded recording/observation chamber (grounded aluminum or copper screen) of sufficient size to permit expression of the behaviors under investigation. Animals should be able to be continuously observed during recording, either through a window in the chamber or via video camera.
  • Low‐noise electrical commutator or slip ring (optional)
  • AC‐coupled differential amplifiers (e.g., model 1700; A.M. Systems)
  • Oscilloscope (digital or analog; storage oscilloscope is optimal)
  • Computer‐based data acquisition/analysis system, including A/D board and software (e.g., CED 1401 Neurophysiological Interface and Spike 2 software; Cambridge Electronic Design)
  • Window discriminator (optional; e.g., model S8; S‐A Instruments)

Support Protocol 1: Preparation of Microwire/Microdrives

  • Enamel glue (e.g., Epoxylite, Epoxylite Corp.)
  • Chemical wire stripper (e.g., Strip‐X; G.C. Electronics)
  • Alcohol swab
  • Normal saline
  • Nichrome microwire (19‐ to 32‐µm uninsulated diameter), double formvar‐insulated, stress relieved, and wound on a large spool to minimize curling (California Fine Wire)
  • Wooden jig (Fig. ), made in‐house
  • 32‐ to 64‐µm support nichrome wire
  • 100°C oven
  • Jeweler's forceps
  • Watch glass
  • Stainless steel soldering flux (e.g., EutecSol Flux; Eutectic Corp.) and rosin core solder
  • Cotton swab
  • Dissecting microscope
  • Fine surgical scissors
  • Impedance meter (e.g., Model BL‐2000; Winston Electronics)
  • 21‐G and 24‐G thin‐wall stainless steel tubing
  • 24‐G needles
  • Moto‐tool with a grinding disk
  • Machine screws, washers, and nuts (all sizes 0 to 80) and a compression spring (Small Parts)

Support Protocol 2: Analyses for Single‐ and Multiple‐Unit Recording Data

  • Rat (adult, 250 to 350 g)
  • 0.9% saline, sterile
  • 0.9% solution of agarose gel (melting point 38°C), kept in a 42°C water bath
  • Dental cement
  • Microdrive (Kopf Instruments or Advanced Machining and Tooling)
  • Stereotrodes or tetrodes (see protocol 5)
  • Stereotaxic manipulator (Kopf Instruments)
  • Surgical instruments
  • 27‐ and 21‐G needles and syringe
  • Anchor screws (00 × ⅛‐in.; Morris Precision Screws and Parts)
  • Miniature electrical connector with sufficient contacts to accommodate the number of wires to be used (Omnetics)
  • Additional reagents and equipment for general surgical procedures (see protocol 1)

Basic Protocol 2: Surgical Implantation of Stereotrodes/Tetrodes and Data Acquisition in Rats

  • Glue or tape
  • Epoxy
  • Gold‐plating solution (Gold NC, Sifco)
  • Round L‐shaped bar, ∼5 mm in diameter with 8‐in. (∼20‐cm) sides
  • Magnetic stir plate
  • Small iron‐containing bar, 3 mm × 8 cm (a size 30 drill bit works well)
  • Flat‐lipped bulldog clip
  • Nichrome or tungsten wire insulated with polyimide: 25‐µm (California Fine Wire) for stereotrodes or 12‐µm (Kanthal H.P. Reid) for tetrodes
  • Heat gun with back‐reflecting attachment (Steinel)
  • Tungsten‐carbide scissors (Fine Science Tools)
  • Solder
  • Microdrive
  • Hollow plastic cylinder, 1 cm diameter × 5 cm long
  • Stainless steel wire
  • Stereotaxic apparatus
  • Stimulus isolation unit (World Precision Instruments)
  • Impedance meter
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Literature Cited

Literature Cited
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   Eichenbaum, H. and Davis, J.L. 1998. Neuronal Ensembles: Strategies for Recording and Decoding. John Wiley & Sons, New York.
   Guzman‐Marin, R., Alam, M.N., Szymusiak, R., Drucker‐Colin, R., Gong, H., and McGinty, D. 2000. Discharge modulation of rat dorsal raphe neurons during sleep and waking: Effects of preoptic/basal forebrain warming. Brain Res. 875:23‐34.
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   McGinty, D. and Szymusiak, R. 1988. Neuronal unit activity patterns in behaving animals: Brainstem and limbic system. Ann.Rev. Psychol. 39:135‐168.
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   McNaughton, B.L., O'Keefe, J., and Barnes, C.A. 1983. The stereotrode: A new technique for simultaneous isolation of several single units in the central nervous system from multiple unit records. J. Neurosci. Methods 8:391‐397.
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   Nitz, D.A. and McNaughton, B.L. 1999. Hippocampal EEG and unit activity responses to modulation of serotonergic median raphe neurons in freely behaving rat. Learning and Memory 6:153‐167.
   Poe, G., Nitz, D.A., McNaughton, B.L., and Barnes, C.A. 2000. Experience‐dependent phase reversal of hippocampal neuron firing during REM sleep. Brain Res. 855:176‐180.
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Key References
   Eichenbaum and Davis, 1998. See above.
  A good review of different spike data analysis methods. Also, provides good descriptions of unit recording methods as applied in different laboratories.
   McNaughton, 1983. See above.
  The first stereotrode paper.
   Rieke, et al. 1999. See above.
  A good review of different spike data analysis methods.
   Wilson, M. and McNaughton, B.L. 2000. Dynamics of hippocampal ensemble code for space. Science 261:993‐994.
  The first tetrode recording paper.
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