Fear‐Potentiated Startle in Mice

William A. Falls1

1 The University of Vermont, Burlington, Vermont
Publication Name:  Current Protocols in Neuroscience
Unit Number:  Unit 8.11B
DOI:  10.1002/0471142301.ns0811bs19
Online Posting Date:  August, 2002
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Pavlovian fear conditioning is frequently used to assess the behavioral, physiological, genetic and molecular correlates of learning and memory. In the typical Pavlovian conditioned fear procedure a neutral stimulus, such as a tone, is paired with a mildly aversive stimulus such as a foot shock. The tone conditioned stimulus (CS) comes to elicit a variety of behaviors that are indicative of learned fear. One of the more prominent of these behaviors is a potentiated acoustic startle response. While fear‐potentiated startle in mice is qualitatively similar to that in rats, the stimulus parameters and procedures for producing optimum fear‐potentiated startle in mice differ considerably from those used in rats. Procedures outlined in this unit include initial assessment of startle, fear conditioning and fear‐potentiated startle testing. Special attention is paid to the parameters that affect the magnitude of fear‐potentiated startle and procedures designed to systematically examine these parameters are included.

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Table of Contents

  • Commentary
  • Literature Cited
  • Figures
  • Tables
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Basic Protocol 1:

  • 8‐ to 24‐week old mice (strains that have been examined include both male and female BALB/cJ, C3H/HeSnJ, C57BL/6J, CBA/J and DBA/2J; all available, e.g., from Jackson Laboratory)
  • Startle apparatus to condition fear and measure startle amplitude: e.g., Med Associates
  • Software‐based sound pressure level (SPL) meter (Med Associates)
  • Constant current shock source: e.g., Med Associates
  • Med Associates shock calibration hardware
  • Software for startle measurement, presentation and sequencing of all stimuli: Med Associates
  • Fine sandpaper
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  •   FigureFigure 8.11.1 Med Associates startle apparatus. The startle apparatus consists of up to 8 sound attenuating cubicles. Each cubicle contains a stabilimiter that consists of an acrylic cylinder mounted on top of a load cell platform and a stimulus panel that is composed of two speakers.
  •   FigureFigure 8.11.2 An example of an analog representation of a startle response recorded from the stabilimiter. Startle responses are transduced by the load cell, amplified, and digitized over a range of 4096 units. Startle amplitude is typically defined as the largest peak‐to‐peak response occurring within 100 msec after the onset of the startle stimulus.
  •   FigureFigure 8.11.3 Bar graph of the noise burst intensity function data shown in Table . In this experiment, 3‐month‐old male ( n = 5) and female ( n = 5) C57BL/6J mice were given the noise burst intensity function test as described in the protocol. Each data point is the peak‐to‐trough startle amplitude recorded in the first 100 msec after the onset of the startle stimulus. Mean startle amplitude is computed for each noise burst intensity and over all three intensities for each mouse. Group averages are computed across all mice. No sex differences were found. Startle amplitude is generally monotonically related to startle stimulus intensity.
  •   FigureFigure 8.11.4 A graphical representation of the fear‐potentiated startle test. The test is depicted on a time line with time moving left to right and top to bottom. The test begins with a 5‐min acclimation period (shown as a broken line). This is followed by 9 leader startle stimuli, 3 each at 100, 105, and 110 dB. The leaders are followed by 18 additional startle stimuli, 6 at each of 100, 105, and 110 dB. One half of the startle stimuli occur at the offset of the 30‐sec, 12‐kHz, 70‐dB tone CS and the remaining half occur in the absence of the tone. The inter‐trial interval (defined as the interval between startle stimuli) is 1 min. As in the initial startle test, each startle stimulus is a noise burst 20 msec in duration with a 0‐msec rise/fall time. Startle is sampled for 100 msec beginning at the onset of each startle stimulus and startle amplitude is defined as the largest peak‐to‐trough response occurring within the 100‐msec sample.
  •   FigureFigure 8.11.5 Bar graph of the fear‐potentiated startle data shown in Table . The tone CS produced little or no change in startle amplitude prior to fear conditioning. However, after fear conditioning the tone produced a significant enhancement of startle amplitude (i.e., fear‐potentiated startle).
  •   FigureFigure 8.11.6 Unconditioned effect of 30‐sec, 70‐dB tones on startle amplitude in three inbred strains of mice. Startle was elicited in the presence and absence of 4, 8, 12, and 16‐kHz tones. In C57 mice, the tones enhanced startle and in C3H mice the tones had little effect on startle, whereas in 129 mice 12 and 16‐kHz tones suppressed startle amplitude. These unconditioned effects can mask subsequent fear‐potentiated startle.
  •   FigureFigure 8.11.7 Change in percent fear‐potentiated startle from the pre‐training to the post‐training tests in C57 and 129 mice trained with either 0.2, 0.4, or 0.6‐mA shock intensities. The change in percent fear‐potentiated startle was computed by subtracting percent fear‐potentiated startle in the pre‐training test from the percent fear‐potentiated startle in each post‐training test.


Literature Cited

Literature Cited
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