Animals in laboratory facilities are exposed to sounds produced by animals and during animal care. Sounds are known to have various physiological effects on animals, but their behavioural consequences are far more obscure. This study was designed to evaluate these consequences. Rats of both sexes and various age groups were housed in a semianechoic soundproof chamber. They were exposed to six sounds: tearing (tearing of paper, noise type), harmonic tone (square wave), pure tone (sine wave), noise (white noise) and two rat screams. It was noticed that rats react with intense startle and flight response when they hear a sudden sound caused by the tearing of ordinary paper. In order to further assess the effect of this type of sound, an additional noise like sound, white noise, was chosen. Responses to sounds with line spectrum, like a rat's own ultrasonic vocalization, were studied by using harmonic tone and pure tone. The tones differed in ultrasonic component allowing assessment of this element as well. Conspecific distress calls were included in order to compare their effects to the fear response of tearing exposure. All sounds were Flayed both at 60 dB(R) and 80 dB(R), weighted according to the auditory sensitivity of rat. Exposure time was 1 s repeated ten times every 30 s. Behaviour was classified and coded from 0 to 7 consisting of no response, listening, movement, startle, and startle with freezing or flight. Vocalization was recorded simultaneously. A tearing sound and noise caused strong startle, flight and freezing at both sound pressure levels, and the structure of these sounds appeared to be a more important factor than the intensity used. Harmonic tone and pure tone induced weak startle, movement and listening or no response at low but stronger response at high sound pressure level. Rat screams elicited movement, listening or no reaction at both sound pressure levels. Rats adapted to all the sounds, although sounds with strong responses required longer adaptation than those eliciting weak responses. Adaptation 'memory' was short and response to the same type of sound was similar even on the following day. Within groups, rats in different cages or from different litters had similar responses. The responses of both sexes were also similar. Animal age was a determinant of response: sensitivity first increased and then decreased with age. Non-pregnant females responded more intensely than pregnant rats, and mothers had the weakest reactions of all the females. Exposure during foetal and suckling time did not change later reactions: the pup group with earlier exposure showed a similar response as pups without such an experience. Rats emitted both audible and ultrasounds. Vocalizations in all groups were occasional and mainly connected with fighting, although ultrasounds not connected with known reasons were also detected. No association was seen between sound exposures and vocalizations. In conclusion, various sounds induce different behavioural patterns in the laboratory rat. In a laboratory animal environment, emphasis should be placed on exclusion of sudden noise type sounds even at low sound pressure levels, while wave type sounds are tolerated by the animals at reasonably high sound pressure levels. Conspecific distress call had little alarm information, and it appears that handling and other routine care procedures resulting in vocalization in rats may not be harmful to other individuals. None of the experimental sounds caused any vocalization and consequently it seems unlikely that these types of sounds as long they an only present in the environment for brief periods have any major effect on communication.
