Step-by-step approach: Stereotaxic surgery for in vivo extracellular field potential recording at the rat Schaffer collateral-CA1 synapse using the eLab system

Abstract

In vivo extracellular field potential recording is a commonly used technique in modern neuroscience research. The success of long-term electrophysiological recordings often depends on the quality of the implantation surgery. However, there is limited use of visually guided stereotaxic neurosurgery and the application of the eLab/ePulse electrophysiology system in rodent models. This study presents a practical and functional manual guide for surgical electrode implantation in rodent models using the eLab/ePulse electrophysiology system for recording and stimulation purposes to assess neuronal functionality and synaptic plasticity. The evaluation parameters included the input/output function (IO), paired-pulse facilitation or depression (PPF/PPD), long-term potentiation (LTP), and long-term depression (LTD).•Provides a detailed picture-guided procedure for conducting in vivo stereotaxic neurosurgery.•Specifically covers the insertion of hippocampal electrodes and the recording of evoked extracellular field potentials.

Keywords: CA1; Hippocampus; In vivo hippocampal extracellular local field potentials recording; Local field potential measurement; Schaffer collaterals; Stereotaxic techniques.

Graphical abstract

Fig. 1

(A) Illustrates the anatomy of the hippocampus and entorhinal cortex pathways. The axons of pyramidal cells from the entorhinal cortex's second layer (II) enter the hippocampus and synapses with the granule cells of the DG and the pyramidal cells of the CA3 region, forming the Perforant pathway. The axons of the granule cells of the DG (Mossy Fiber) then synapse with the pyramidal cells of the CA3 region. The axons from CA3 pyramidal cells (Schaffer collaterals) enter the CA1, synapsing with the proximal dendrites of the CA1 area. The CA1 axons then project back to the deeper layer of the entorhinal cortex (layer V), creating an anatomical and functional loop. Also, the axons from layer III of the entorhinal cortex (Temporoamonic pathway) enter the CA1 and synapse with the distal dendrites. (B) The figure also includes a schematic view of (i) an animal placed onto a stereotaxic device, (ii) the exposed skull, determination of the bregma and lambda, finding the coordinate of Schaffer collaterals and CA1, (iii) drilling the marked location, and (iv) insertion of both stimulatory and recording electrodes. This figure was created with BioRender.com.

Fig. 2

The two-arm stereotaxic device is equipped with three micromanipulators that enable movement in three dimensional spaces along the X (medio-lateral/ML), Y (antero-posterior/AP), and Z (dorso-ventral/DV) axes. The device includes microdrive screw adjustments for the AP, ML, and DV axes ([1], [2], [3]), also ear bars (4), an incisor bar (5), and two holders for left and right device arms (6).

Fig. 3

A picture-guided neurosurgery was performed prior to electrode insertion. (A) The rat was mounted onto a two-arm stereotaxic device, with the left side ear bar in place, while the left hand supports the animal. (B) The right ear bar was then loosened and placed into the auditory canal. (C) The rat's tongue was retracted to the side using forceps. (D) The scalp was excised using fine scissors; (E, F) the bregma (Br) and lambda (La) were identified and temporarily marked using a pointer (gauge 27); (G) a dental micromotor hand drill was used to perform craniotomy and make four pilot holes at the corners of the marked locations (right side for Schaffer collaterals, and left side for CA1) and; (H) the dura mater was pierced using a needle (gauge 27).

Fig. 4

Inserting stimulation and recording electrodes. (A) Replace the guide cannula with the bipolar stimulation electrode on the right arm of the stereotaxic frame; (B) Place the tip of the stimulation electrode on the bregma; (C) Insert the stimulation electrode after calculating the coordinates; (D) Place the recording electrode on the left arm of the device (angled at 52.5 degrees); (E) Place the tip of the recording electrode on the bregma; (F) Insert the recording electrode after calculating the coordinates.

Fig. 5

View the eLab design protocol page for the followingparameters: (A-1) Stimulation parameters. (A-2) Recording parameters. (B) Mixer section to activate stimulator. Refer to the text for more details. (C) A putative waveform with the definition of the protocol parameters.

Fig. 6

Histological image of the right hippocampus. In the top photos, the stimulatory electrode was placed on the Schaffer collaterals (left) and the recording electrode was placed on CA1 (right). In the bottom photos, red stars indicate the coordinates of Schaffer collaterals (left) and CA1 (right) on the Paxinos atlas.

Fig. 7

(A) EPSPs recorded from the IO 100-1000, with 10 different intensities labeled as a-j. (B) Paired pulses were recorded at intervals of 10, 20, 30, 50, 70 and 100 ms, labeled as a-f. (C) EPSPs were recorded before LTP / LTD induction (a), after LTP induction (b), and after LTD induction (c).