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.