Motivated attention and prepulse inhibition of startle in rats: Using conditioned reinforcers as prepulses.

In humans, prepulse inhibition (PPI) of startle is greater during attended prestimuli than it is during ignored prestimuli, whereas in rats, most work has focused on passive PPI, which does not require attention. In the work described in this article, researchers developed a paradigm to assess attentional modification of PPI in rats using motivationally salient prepulses. Water-deprived rats were either conditioned to attend to a conditioned stimulus (CS; 1-s, 7-dB increase in white noise) paired with water (CS+ group), or they received uncorrelated presentations of white noise and water (CSo group). After 10 conditioning sessions, startle probes (50 ms, 115 dB) were introduced, with the CS serving as a continuous prepulse. Three experiments examined PPI across a range of prepulse intensities (4-10 dB) and stimulus onset asynchronies (SOAs; 30-960 ms). PPI was consistently reduced in the CS+ group, particularly with a 10-dB prepulse and a 60-ms SOA. Thus, PPI in rats differed between attended and ignored prestimuli, but the effect was reversed in the results of research with humans. A fourth study eliminated the group difference by reversing the CS-water contingency. Methodological and motivational hypotheses regarding the current findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in prepulse inhibition (PPI) between Wistar and Sprague-Dawley rats clarified by a new method of PPI standardization.

Rat strain differences in the acoustic startle response (ASR) and prepulse inhibition (PPI) of that response are of increasing interest, especially as the genetics of PPI may provide an approach to studying the genetics of certain mental illnesses. However, strain differences in PPI are confounded by differences in ASR. To clarify this issue, the authors investigated the ASR and PPI across a range of startling stimulus intensities (70 dB-120 dB) in Wistar and Sprague-Dawley rats (N=96). Sprague-Dawleys showed more PPI of ASR capacity (response limit) than Wistars. In contrast, Wistars exhibited greater PPI than Sprague-Dawleys, as measured by an increase in response threshold. This dissociation suggests that PPI is more complex than that assessed by single startling stimulus intensity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory fear conditioning modulates prepulse inhibition in socially reared rats and isolation-reared rats.

Prepulse inhibition (PPI) is the reduction of the startle reflex when the startling stimulus is shortly preceded by a non-startling stimulus. Previous studies have shown that PPI in rats can be enhanced by auditory fear conditioning (AFC) but weakened by isolation rearing. This study investigated whether isolation rearing affects the effect of AFC on PPI. The results show that PPI was lower in isolation-reared rats than that in socially reared rats, and it was markedly enhanced by AFC in socially reared rats. However, the AFC-induced PPI enhancement in isolation-reared rats was much lower than that in socially reared rats. Moreover, the AFC-induced PPI enhancement was blocked by intraperitoneal injection (1 mg/kg) of the selective antagonist of metabotropic glutamate receptor subtype 5 (mGluR5), 2-methyl-6-(phenylethynyl)-pyridine (MPEP), 30 minutes before AFC. The baseline startle was also enhanced by isolation rearing. Thus, isolation rearing impairs not only PPI but also the AFC-induced PPI enhancement, which depends on mGluR5 activity. This study advances the animal model for investigating both neural bases and cognitive features of schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral effects of psychomotor stimulants in rats with dorsal or ventral subiculum lesions: Locomotion, cocaine self-administration, and prepulse inhibition of startle.

Compelling evidence suggests a primary role for the mesoaccumbens dopaminergic pathway in the behavioral effects of amphetamine and cocaine, but the roles of other projections to the accumbens, including those arising in the hippocampal formation, are less clear. The authors evaluated the effects of discrete excitotoxic lesions of either the dorsal or ventral subiculum on the locomotor activating, reinforcing, and sensorimotor gating-disruptive effects of psychomotor stimulant drugs. Whereas dorsal subiculum-lesioned rats were hyperactive in tests of exploratory locomotion and startle reactivity, ventral subiculum-lesioned rats exhibited an attenuated locomotor response to amphetamine, moderately impaired acquisition of cocaine self-administration, and reduced levels of prepulse inhibition of startle. These 2 behavioral profiles overlap considerably with those previously observed in rats with lesions of the rostrodorsal and caudomedial accumbens, respectively, and suggest that projections from dorsal subiculum to accumbens core and ventral subiculum to accumbens shell exert distinct influences on behavioral responses that are amplified by psychomotor stimulant drugs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)