Acoustic Startle Reflex of Wistar Rats. Methodical Elaboration and Validation in Experiment

The natural startle reflex, characteristic of both animals and humans, is a short and intense defense reaction in response to an unexpected strong external stimulus. In experiments, this reflex is often triggered by a short sound stimulus (acoustic startle reflex—ASR). The amplitude of the ASR and the degree of its dependence on modulating factors, such as the preceding weak stimulus (prepulse), serve as markers of the state of sensorimotor gating regulation and are widely used in neuropsychiatry and neurophysiology to assess disorders of mental functions. The amplitude value of the ASR is a critical factor of assessment, and the accuracy of its determination depends on many technical conditions: the design of the experimental setup, 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 describes a methodological development for measuring ASR and its prepulse inhibition (PPI), which includes an original working chamber, hardware and software, and an optimal testing protocol. During validation of the methodology on a group of outbred rats (Wistar), it was found that (1) the methodology allows us to assess the heterogeneity of the group by the amplitude of the ASR and to perform the corresponding phenotypic clustering of the animals and (2) repeated, after 7 days, testing of ASR and PPI in the same animals does not disturb their initial clustering and does not significantly change the measured parameters. These observations allow us to consider the methodology applicable to sequential testing of the same group of animals before and after experimental exposure, taking into account the dependence of the result on the cluster membership of the subgroups determined during the first test.