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

The natural startle reflex, characteristic of both animalsand humans, is a short and intense defense reaction in responseto an unexpected strong external stimulus. In experiments, thisreflex is often triggered by a short sound stimulus (acoustic startlereflex—ASR). The amplitude of the ASR and the degree of its dependenceon modulating factors, such as the preceding weak stimulus (prepulse),serve as markers of the state of sensorimotor gating regulationand are widely used in neuropsychiatry and neurophysiology to assessdisorders of mental functions. The amplitude value of the ASR isa critical factor of assessment, and the accuracy of its determinationdepends on many technical conditions: the design of the experimentalsetup, the type and location of the mechanical-electrical sensor,the method of digitization and presentation of primary data, theprotocol of the experiment, etc. This issue describes a methodologicaldevelopment 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 methodologyon a group of outbred rats (Wistar), it was found that (1) the methodologyallows us to assess the heterogeneity of the group by the amplitudeof the ASR and to perform the corresponding phenotypic clusteringof the animals and (2) repeated, after 7 days, testing of ASR andPPI in the same animals does not disturb their initial clusteringand does not significantly change the measured parameters. Theseobservations allow us to consider the methodology applicable tosequential testing of the same group of animals before and afterexperimental exposure, taking into account the dependence of theresult on the cluster membership of the subgroups determined duringthe first test.