Acoustic startle reflex of Wistar rats. Methodical elaboration and validation in experiment

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Abstract

The natural fear reflex, characteristic of both animals and humans, is a short and intense defensive reaction in response to a strong and unexpected external stimulus. In experiments, this reflex is often triggered by a strong and short sound stimulus (acoustic flinch reflex – ASR). The amplitude of the ASR and the degree of its dependence on modulating factors, such as a previous weak stimulus (prepulse), serve as markers of the state of sensorimotor gating and are widely used in neuropsychiatry and neurophysiology to assess disorders of mental functions. The magnitude of the ASR amplitude is a critical evaluation factor, and the accuracy of its determination depends on taking into account many technical conditions: the design of the experimental installation, the type and location of the mechanical-electrical sensor, the method of digitization and presentation of primary data, the protocol of the experiment, etc. This issue presents a methodological development for measuring ASR and its prepulse inhibition (PPI), which includes an original working camera, hardware and software, as well as an optimal testing protocol. During validation the technique on a group of outbred rats (Wistar), it was found that (1) the technique allows us to assess the heterogeneity of the group by the amplitude of ASR and conduct appropriate phenotypic clustering, and (2) repeated, after 7 days, testing of ASR and PPI in the same animals does not violate their initial clustering and does not significantly changes the measured parameters. These observations allow us to consider the methodology applicable for sequential testing of one group of animals before and after any experimental exposure, taking into account the dependence of the result on the cluster membership of the subgroups determined during the first test.

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D. G. Semenov

Pavlov Institute of Physiology of the Russian Academy of Sciences

Author for correspondence.
Email: dsem50@rambler.ru
Russian Federation, St. Petersburg

A. V. Belyakov

Pavlov Institute of Physiology of the Russian Academy of Sciences

Email: dsem50@rambler.ru
Russian Federation, St. Petersburg

V. N. Chikhman

Pavlov Institute of Physiology of the Russian Academy of Sciences

Email: dsem50@rambler.ru
Russian Federation, St. Petersburg

S. D. Solnushkin

Pavlov Institute of Physiology of the Russian Academy of Sciences

Email: dsem50@rambler.ru
Russian Federation, St. Petersburg

References

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2. Fig. 1. Installation diagram for registering the ASR. 1 – Working chamber (detachable pipe), 1a – upper half, 1b – lower half, 1c – transparent plugs fixed to the upper half, 1d – opening line. 2 – Chamber base. 3 – Spring. 4 – Accelerometer sensor. 5 – Controller board. 6 – USB connector. 7 – Double bearing block. 8 – Upper (removable) part of the outer box. 9 – Lower part of the outer box. 10 – Video camera. 11 – Speakers. 12 – Fan. 13 – LED backlight. 14 – Connection to a PC and power supplies.

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3. Fig. 2. Graphical representation of the reactions of one rat to a series of double stimuli on the monitor screen. The horizontal axis shows the latent period values ​​of the muscle response peaks in “counts” from the onset of the weak stimulus (in this graphic derivation, 1 count = 6 ms), the leading edge of the strong stimulus is marked with an arrow. The vertical axis shows the amplitude of the responses in relative units. The right column shows the interactive selection of recording the reactions to the entire series of stimuli (a) or the reaction to a specific stimulus in the series (b). In the scan (b), the cursor moved to the peak shows its amplitude and latency. In the latency area “15”, a wave of response to a weak prepulse is noticeable, in the latency area “30”, the peaks of the earliest responses to a strong stimulus are located.

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4. Fig. 3. Clustering of the group of naive Wistar rats by the values ​​of ASR amplitudes and PPT strength. (a) – LR subgroup – on the left, HR subgroup – on the right. The lines connect the mean values ​​of ASR amplitudes for each animal, obtained for single strong stimuli (base) and for double stimuli (double). The gray dotted line connects the median values ​​for the subgroups with the indication of the values. (b) – clustering into LR and HR subgroups, obtained taking into account the mean ASR amplitudes for each of the successive strong stimuli (LR, n = 15; HR, n = 8; mean ± SEM; p < 0.001). (c) – comparison of the mean PPT values ​​of the two clusters (LR, n = 15; HR, n = 8; med ± SEM; p = 0.03).

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5. Fig. 4. Comparison of the values ​​of the ASR amplitudes during the first and repeated (after 7 days) testing. (a) – LR cluster, (b) – HR cluster. The designations are the same as in Fig. 3, a.

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