Pharmacological manipulation of ultrasound induced defence behaviour in the rat

Rats exposed to aversive stimuli display species specific defence behaviour as part of their natural survival strategy. One component of this behaviour is the production of ultrasonic calls in the 20 to 27-kHz range, which are thought to serve a communicative role. The present study has examined the behavioural effects of exposing rats to artificially generated ultrasound and the ability of three distinct pharmacological agents to modify this response. Single tone 20 kHz ultrasound exposure for 1 min produced intensity-related locomotor behaviour, characteristic of defence behaviour, which could be measured using a computer tracking system, This was significantly reduced by peripheral pretreatment with the benzodiazepine, diazepam (0.3 and 3.0 mg/kg IP). Pretreatment with the 5-HT agonist 1-(3-chlorophenyl) piperazine (mCPP) (0.5-2.0 mg/kg IP) produced a dose-related reduction in the ultrasound-induced response, The alpha(2) adrenoceptor antagonist, yohimbine (0.5-5.0 mg/kg IP), caused an increase in the response at the lower dose (0.5 mg/kg) and a decrease at the two higher doses (2.0 and 5.0 mg/kg). The,resent findings suggest that defence behaviour in the rat can be artificially produced by 20 kHz ultrasound; this is sensitive to pharmacological manipulation and may offer a novel animal model of aversive behaviours that are associated with human panic.