Startle responses, heart rate, and temperature in 5-HT1B receptor knockoutmice

Relative to wildtype mice, mice lacking 5-HT1B receptors (5HT-(1B) KO) exhi bit exaggerated heart rate and body temperature responses to environmental stimuli. In contrast, acoustic startle reactivity is reduced in 5-HT1B KO m ice. We combined heart rate and temperature measurement with startle respon se paradigms in order to elucidate this apparent contradiction. Habituation and footshock-induced sensitization paradigms modulate startle reactivity. Reduced startle reactivity and unaltered habituation in 5-HT1B KO mice wer e replicated. Heart rate and temperature were unaffected by startle stimuli , but increased markedly in response to transportation and handling procedu res. Footshocks caused a mild startle-sensitization and tachycardia in both genotypes. The physiological hyper-reactivity in 5-HT1B KO mice is a subtl e phenotypic difference that contrasts with the phenotypic decrease in star tle reactivity. NeuroReport 11:4097-4102 (C) 2000 Lippincott Williams & Wil kins.