| Abstract No.: | B-D2148 |
| Country: | Canada |
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| Title: | THE EFFECTS OF LIPOPOLYSACCHARIDE ON THE TACTILE STARTLE RESPONSE AND PREPULSE INHIBITION: EVIDENCE FOR DECREASED STARTLE WITH SICKNESS
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| Authors/Affiliations: | 1 Andrew Lockey*; 1 Martin Kavaliers; 1 Klaus-Peter Ossenkopp;
1 The University of Western Ontario, London, ON, Canada
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| Content: | OBJECTIVES: This study examined the dose-dependent effects of Lipopolysaccharide (LPS) administration on the tactile startle response (TSR) and prepulse inhibition (PPI) in male Long-Evans rats. Testing was repeated 72 hours after initial exposure to LPS in order to assess tolerance effects. MATERIALS AND METHODS: The rats were injected intraperitoneally with LPS (50, 100 or 200 μg/kg in 0.9% saline, n = 8 for each) or saline vehicle (n = 10) at volumes of 1ml/kg body weight on 2 Test Days. At one hour after each treatment, subjects were placed in a non-novel startle box apparatus producing background white noise at 70 dB. The rats were then exposed to 10 startle-alone trials in order to acclimatize the rats and reduce variability in responses before test data was collected. Startle responses were recorded following air-puff-alone trials (15 psi) and trails containing auditory-prepulses of varying intensities (+3, +6 and +12 dB above background noise) presented 120ms before startle air-puff stimuli. RESULTS: The results revealed an effect of Prepulse Level, where trials with louder prepulses elicited greater inhibition of the startle response. The was also a Main Effect of Day such that prepulses of all intensities were more effective in inhibiting the startle response on the second test day relative to Test Day 1. Analysis of startle-alone trials indicated that the Amount of LPS produced a linear trend, with the 200 μg LPS group eliciting the lowest startle response and saline the highest. Also, a Day x Drug interaction was found, indicating that LPS produced a decrease in TSR on startle responses, but this decrease became less pronounced on the second test day. CONCLUSIONS: LPS reduced the behavioural TSR in a dose-dependent manner. The TSR showed tolerance to LPS administration, possibly due to less motor inhibition resulting from decreased immune activation. These startle-only results are consistent with our acoustic startle response data, indicating that the range of sickness behaviours following LPS-administration to adult rats includes a global decrease in motor responses including non-voluntary motor activity. Auditory prepulses were effective in producing inhibition of the tactile startle response; however, variability of prepulse effectiveness across test days suggests cross-modal prepulse measures are subject to significant modulation with repeated exposure. |
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