Enhancement of the acoustic startle reflex by an alarm pheromone in male rats.
Recently, we reported that an alarm pheromone released from the perianal region of male rats aggravated stress-induced hyperthermia and increased defensive and risk assessment behaviors in recipient male rats. Based on these results, we hypothesized that the primary effect of the alarm pheromone is to increase anxiety; however, there is still no clear evidence for this pheromone effect. Therefore, we examined this issue by assessing the effect of the alarm pheromone on the acoustic startle reflex (ASR), which is a useful index for studying negative emotions such as anxiety in rats. The alarm pheromone enhanced the ASR for 105-dB auditory stimuli, but not for those of 90 and 120 dB, when these three intensities of sound were used randomly. The same results were obtained when one of these three intensities was used repeatedly. In addition, pretreatment with diazepam (i.p.) at doses of 0.7 and 2.0 mg/kg suppressed the ASR of the pheromone recipients, whereas the lower dose (0.2 mg/kg) slightly attenuated the pheromone effect and the control injection (vehicle) had no effect. These results indicate that the alarm pheromone enhances the ASR by increasing anxiety in recipient rats, suggesting that the primary effect of the alarm pheromone is to increase the anxiety level.
Laboratory of Veterinary Ethology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. ahinaga@mail.ecc.u-tokyo.ac.jp <ahinaga@mail.ecc.u-tokyo.ac.jp>
Hideaki
H
Inagaki
Yasushi
Y
Kiyokawa
Takefumi
T
Kikusui
Yukari
Y
Takeuchi
Yuji
Y
Mori
D000161:Acoustic Stimulation / Q000379:methods; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003975:Diazepam / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D008297:Male; D011897:Random Allocation; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D013216:Reflex, Startle / Q000187:drug effects* / Q000502:physiology; D012724:Sex Attractants / Q000378:metabolism* / Q000494:pharmacology*
D006993:Hypnotics and Sedatives; D012724:Sex Attractants; D003975:Diazepam