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. 2012 Jul;108(2):697-707.
doi: 10.1152/jn.00910.2011. Epub 2012 Apr 18.

Friction-based Stabilization of Juxtacellular Recordings in Freely Moving Rats

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Free PMC article

Friction-based Stabilization of Juxtacellular Recordings in Freely Moving Rats

Lucas Herfst et al. J Neurophysiol. .
Free PMC article

Abstract

Virtually nothing is known about the activity of morphologically identified neurons in freely moving mammals. Here we describe stabilization and positioning techniques that allow juxtacellular recordings from labeled single neurons in awake, freely moving animals. This method involves the use of a friction-based device that allows stabilization of the recording pipette by friction forces. Friction is generated by a clamplike mechanism that tightens a sliding pipette holder to a preimplanted pipette guide. The interacting surfaces are smoothed to optical quality (<5-nm roughness) to enable micrometer stepping precision of the device during operation. Our method allows recordings from identified neurons in freely moving animals, and thus opens new perspectives for analyzing the role of identified neurons in the control of behavior.

Figures

Fig. 1.
Fig. 1.
Mechanics of the friction-based device. A: top view of the assembled device. Boxes highlight the friction clamp (1), the central core (2) with friction interface indicated in red, and the pipette-holding arm (3). Modified from Burgalossi et al. (2011), with permission from Elsevier. B: 3-dimensional view of the assembled device with the recording pipette in position. The friction interface is highlighted in red. C: color-coded maximal translations of the device according to finite element method (FEM) simulation under the application of 106 mN (arrows), corresponding to the assumed 5 g maximal acceleration of the rat (see methods). The base of the pipette guide is the fixed point. Maximal translation of the pipette tip is shown. D: schematic representation showing the position of the individual implanted components relative to a rat's head.
Fig. 2.
Fig. 2.
Steps and performance of the juxtacellular recording technique in freely moving animals. A: schematic representation of the steps to perform juxtacellular recordings in freely moving animals. Time 0 refers to the initial establishment of the juxtacellular configuration. Note that the “agarose” step can also be performed before, and not necessarily after, establishing the juxtacellular configuration. Components modified from Burgalossi et al. (2011), with permission from Elsevier. B: recording electrode with long thin taper used for juxtacellular recordings. Inset: higher magnification of the tip. C: average firing rates computed during the 1st minute of juxtacellular recording (“initial”), “before labeling,” and “before release” of the animal from the head-fixation frame. The averages are calculated separately for all neurons (n = 83, black) and without the 2 fast-spiking cells (−FS) in our data set (n = 81, gray). Error bars represent SD. D: overview of the performance of the friction device for obtaining juxtacellular recordings in freely moving animals: 28% of the experiments were interrupted because of inability to obtain stable juxtacellular recordings (“aborted experiments”); the percentages for “anchoring-transfer losses,” “wake-up losses,” and “freely moving recordings” refer to the subset of experiments (72%) in which 1 stable juxtacellular recording in the target region was obtained and stabilization was attempted by application of acrylic (“anchoring attempts”).
Fig. 3.
Fig. 3.
Stability of spike signals during freely moving animal behavior. A: distribution of the initial peak-to-peak spike amplitudes, calculated as the average during the first 10% of each freely moving recording session. B: distribution of spike amplitudes over time for all freely moving recordings. Recording duration was normalized; bin size = 10%. Error bars represent SE. C and D, top: representative recordings where spike amplitudes were either stable (C) or slowly decreased during the freely moving recording session (D). On top, representative spike waveforms from the beginning and the end of each recording session are shown. Bottom: speed plots for the corresponding plots shown above (same timescale). E and F: representative raw spike traces for the recordings shown in C and D, respectively.
Fig. 4.
Fig. 4.
Juxtacellular recording durations during freely moving behavior. A: distribution of recording durations for all deliberately terminated freely moving juxtacellular recordings (n = 83). B: distribution of recording durations for a subset of unterminated freely moving juxtacellular recordings (n = 12) targeted to the dorsal hippocampus. C: average ± SD spike amplitudes (bin size = 1 min) for the longest freely moving unterminated recording shown in B (total duration = 3.3 h). Inset: superimposed normalized spike waveforms at the beginning (red) and end (black) of the recording session.
Fig. 5.
Fig. 5.
Identified silent cells in freely moving animals. A, left: reconstruction of the somatodendritic (red) and axonal (blue) morphology of a layer 5 pyramidal neuron in medial entorhinal cortex with a superimposed outline of small layer 2 patches (light brown) identified by cytochrome oxidase staining. D, dorsal; V, ventral; A, anterior; P, posterior. Right: micrograph of the biocytin-labeled neuron reconstructed on left. Scale bar, 50 μm. B, top: representative unfiltered and high-pass-filtered spike traces recorded from the cell shown in A before the animal woke up and explored the arena. A magnification of the spike is shown. Note the slow wave oscillations (∼1 Hz) during anesthesia in the unfiltered trace. Bottom: speed plot corresponding to the traces shown above. C, top: representative unfiltered and high-pass-filtered spike traces recorded during freely moving behavior from the same cell shown in A. Note the faster LFP oscillations compared with the anesthetized period and the absence of spikes. Bottom: speed plot corresponding to the traces shown above. D: trajectory of the rat (gray) during running in a 120 × 60-cm “O”-shaped maze. E: action potential firing (top) induced by squared current pulses of increasing amplitude (bottom) for the cell shown in A. These pulses were delivered at the end of the freely moving recording session to confirm the presence of the silent cell. Note that this cell kept discharging after the current pulse. Asterisks indicate stimulation artifacts (truncated for display purposes).

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