Development of the auditory startle reflex in juvenile Wistar rats
The Auditory Startle Reflex (ASR) is a transient motor response mediated by the brainstem to an unexpected, intense acoustic stimulus. It represents a sensitive, non-invasive measurement of central nervous system activity and can be applied to assess auditory function and cerebral gating ability. During ASR measurement, the latency, intensity and duration of the reaction to a sudden short acoustic signal is quantified, the habituation to a repeated signal is assessed and the pre-pulse inhibition (the reduced startle reflex after a "warning" signal) can be measured. Increases in the response to acoustic stimuli and a shorter latency are described in Attention-Deficit Hyperactivity Disorder (ADHD) and fragile X-syndrome while a decrease or lack in habituation can be seen in post-traumatic stress disorder and schizophrenia. In order to track the development of reflex response in juvenile rats, litters of juvenile Wistar WU were exposed to a pre-defined program of acoustic stimuli at 10, 15, 20, 40 and 60 days post partum (pp) and the intensity and duration of the response to acoustic stimuli as well as the progress in pre-pulse inhibition and habituation were measured. Our results demonstrate the practicability of ASR measurements as early as day 10 pp with a coordinated animal response showing a significant pre-pulse inhibition around day 15 pp, in coincidence with ear and eye opening. During the juvenile period of hyperactivity and -reactivity (around day 15-20 pp) the juvenile rats show high intensity reactions with a long duration. The development of a gender-specific response starts around day 40 pp in coincidence with sexual maturation, with females demonstrating a higher degree of habituation and pre-pulse inhibition. Adult-like patterns of habituation can be assessed by day 60 pp. In contrast to general experimental habit (assessing ASR at weaning and day 60 pp), our data demonstrate the practicability of ASR measurement at day 15 pp with comparable results, enabling an earlier assessment of cerebral function.