Date of Award

1-1-2009

Document Type

Campus Access Thesis

Department

Psychology

Sub-Department

Experimental Psychology

First Advisor

Charles F. Mactutus

Abstract

Prepulse inhibition (PPI), employed as a measure of sensorimotor gating, is operationally defined by the presentation of a weak (prepulse) stimulus immediately prior to a startling stimulus, causing a reduction in the magnitude of the startle response. Alterations in gating are observed in individuals with neuropsychiatric disorders such asTourette's syndrome and Huntington's Disease, as well as neurodevelopmental disorders such as schizophrenia, and ADHD , and in rats after treatment with certain classes of drugs, including dopamine agonists. Because of the relative loss of PPI in inherited developmental disorders such as schizophrenia, there is great interest in understanding the developmental features of PPI (the present study) as well as its neurochemical regulation. Despite the growing wealth of PPI literature, the majority of the published papers are limited to testing one sensory system at one age. The present study is a continuation of our research assessing whether PPI response curves differ as a modality of the prepulse as well as the maturation of such curves across early development. In the present study, we replicated an earlier study (Parisi and Ison, 1979, 1981) to include three different sensory system prepulse stimuli across three different ages (postnatal days (PD)15, 18, 31, 35, and PD 90) in Long- Evans rats. Peak amplitude and latency response curves were assessed for visual and auditory prepulse modalities across interdigitated trials for auditory (85dB(A) prepulse white noise) and visual (200 lux, white LED) prepulses (20 msec) for PPI [70dB(A) background, 5-min acclimation period, 6 ASR trials, 72 PPI trials (ISIs of 0, 8, 40, 80, 120, and 4000 ms, 6-trial blocks, v Latin square design)]. Peak amplitude curves for tone and tactile were similar in shape across age with peak inhibition observed at 40 msec. Latency curves for tactile were similar in shape across age. Latency curves for tone revealed a difference between the younger (PD 18) and older (PDs 35 and 90) animals, highlighting the relatively early maturation in the auditory sensory system. However, a profound difference across age was found in visual PPI peak amplitude and latency curves. Animals at PD 18 and 35 show a low, flat amplitude, whereas the adult animals show a more defined curve with peak inhibition observed at 40 msec. The prominent developmental differences suggest that the younger animals are not processing the visual prepulse as well as the adult animals due to the relatively late maturation of the visual sensory system in the rat. Collectively, these results indicate PPI response curves are contingent on the maturation level of the sensory system of interest. The more precise characterization of the development of PPI across sensory modality should enhance the utility of the PPI model for neuropsychiatric and developmental disorders and studies of its neurochemical regulation.

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