5-HT1B receptor knockout, but not 5-HT1A receptor knockout mice, show reduced startle reactivity and footshock-induced sensitization, as measured with the acoustic startle response

To investigate whether the hyperreactivity to mild environmental and novel stimuli in 5-HT1B receptor knockout (1BKO) mice, as suggested by measures o f exploratory, aggressive, and impulsive behaviors, can be extended to phas ic stimuli, 1BKO and wildtype mice were tested in acoustic startle reactivi ty and plasticity paradigms, including habituation, prepulse inhibition, an d footshock-induced sensitization of the startle response. Furthermore, we compared 5-HT1A receptor knockout (1AKO) and 1BKO mice to further test the suggested opposite behavioral profiles in these two genotypes. Results show that startle reactivity and Footshock-induced sensitization was reduced in 1BKO mice, with no changes in habituation or PPI. In contrast, 1AKO mice d id not differ from WT mice in any of the measures. These results indicate t hat an absence of 5-HT1B receptors, but not of 5-HT1A receptors, affects th e modulation of startle reactivity and footshock-induced sensitization, wit hout influencing startle plasticity. Moreover, this study suggests that 1AK O mice display a distinct, but not opposite behavioral profile from 1BKO mi ce. Furthermore, it is concluded that the hyperreactivity in 1BKO mice cann ot be generalized to all stimuli, including the startling stimuli used in t his study, but is probably restricted to mild environmental stimuli only. ( C) 2001 Elsevier Science B.V. All rights reserved.