STRAIN AND AGE-DIFFERENCES IN ACOUSTIC STARTLE RESPONSES AND EFFECTS OF NICOTINE IN RATS

Two experiments examined the effects of age, genetic strain, and nicot ine on acoustic startle response (ASR) amplitude and prepulse inhibiti on (PPI) in rats. ASR amplitude measures reactivity to external stimul ation, and PPI is used as an index of sensory gating related to attent ion. Both ASR amplitude and PPI have been previously reported to be in creased by nicotine in adult rats. Experiment 1 examined effects of ch ronically administered nicotine and saline on ASR and PPI in Wistar, L ong-Evans, and Sprague-Dawley rats (40 days of age). Experiment 2 exam ined the effects of chronically administered nicotine and saline in Sp rague-Dawley rats of two age groups: 40 and 70 days of age at the begi nning of the study. ASR amplitude differed significantly across strain s with the values for Wistar > Sprague-Dawley > Long-Evans, and there were no differences in percent of PPI among the three strains. In addi tion, results of Experiment 2 indicated that older rats had significan tly greater ASR amplitudes and PPI than younger rats. Consistent with previous reports, nicotine increased ASR and PPI in the older rats; ho wever, there were no significant differences in the younger rats. Ther efore, age and genetic strain are important variables in the analysis of nicotine's effects on startle behaviors in rats.