Environmental noise can alter endocrine, reproductive and cardiovascular function, disturb sleep/wake cycles, and can mask normal communication between animals. These outcomes indicate that noise in the animal facility might have wide-ranging affects on animals, making what laboratory animals hear of consequence for all those who use animals in research, not just the hearing researcher. Given the wide-ranging effects of noise on laboratory animals, routine monitoring of noise in animal facilities would provide important information on the nature and stability of the animal environment. This special issue will highlight the need for more thorough monitoring and will serve as an introduction to noise and its various effects on animals.

The purpose of this article is to provide directors of animal care facilities with a basic understanding of some of the principles of acoustics and the measurement of sound. This knowledge likely will enable directors to work effectively with sound and hearing specialists at their institutions to monitor and control the acoustic environments of laboratory animal facilities.

Any attempt to assess the effects of sounds on animals must consider species differences in hearing abilities. Although the hearing ranges of most species overlap to a large degree, considerable variation occurs in high- and low-frequency hearing as well as in absolute sensitivity. As a result, a sound that is easily audible to one species may be less audible, or even inaudible, to another. The purpose of this review is to describe the variation in the hearing ranges of common laboratory animals.

The auditory system of rodents and other animals is affected by numerous genetic and environmental variables. These include genes that cause hearing loss, exposure to noise that induces hearing loss, ameliorative effects of an augmented acoustic environment on hearing loss, and effects of background noise on arousal. An understanding of genetic and environmental influences on hearing and auditory behavior is important for those who provide, use, and care for laboratory animals.

Many laboratory rodents emit ultrasonic vocalizations. The purpose of this review is to highlight the types and functions of ultrasonic vocalizations emitted by laboratory rats and mice. Rats emit 3 types of ultrasonic vocalizations, depending on the animal's age, its environmental conditions, and its affective state. Rat pups emit a 40-kHz vocalization when they are separated from their mothers. Adult rats emit a 22-kHz vocalization in anticipation of inescapable aversive stimuli. These two types of vocalizations reflect a negative affective state of the animal. Rats produce a 50-kHz vocalization under nonaversive conditions, and these vocalizations reflect a positive affective state of the animal. Adult mice produce several different types of ultrasonic calls that can be classified as different syllables. Mice produce ultrasonic vocalizations during nonaggressive interactions, particularly during mating behaviors, but these vocalizations are not indicators of negative or positive affect. Therefore, the function of ultrasonic vocalizations in adult mice is likely only to facilitate or inhibit social interactions. Understanding the types and functions of ultrasonic vocalizations emitted by laboratory rodents may enable researchers and animal care personnel to use vocalizations as an indicator of an animal's behavior and affect.

Noise has both auditory and extra-auditory effects. Some of the most deleterious extra-auditory effects of noise are those leading to sleep disturbances. These disturbances seem to be related to both endogenous (physical parameters) and exogenous (sex, age) factors of noise. Despite correlative relations between noise level and awakenings, the scientific community has not reached consensus regarding a specific action of these factors on the different sleep stages. In animal research, 2 complementary main fields of research exist. One is focused on the positive modulation of sleep by repeated tone stimulation. The other concerns noise-related sleep disturbances. The few studies that have investigated noise-related sleep disturbances suggest the following conclusions. First, sleep disturbances are greater upon exposure to environmental noise, whose frequency spectrum is characterized by high and ultrasonic sounds, than white noise. Second, unpredictability and pattern of noise events are responsible for extractions from both SWS and PS. Third, chronic exposure to noise permanently reduces and fragments sleep. Finally, in chronic noise exposure, an inter-individual variability in SWS deficits is observed and correlated to a psychobiological profile related to an incapability to face stressful situations. Based on results from other research, acute noise-related sleep perturbations could result from an imbalance in the sleep–wake cycle in favor of arousing ascending systems. Chronic noise-related sleep disturbances may arise due to imbalance of the sleep-wake cycle and malfunctioning of the hypothalamo-pituitary-adrenal axis which may both contribute to the development of pathology.

Here we discuss the importance of monitoring noise in contemporary animal facilities. Noise surveys and monitoring should be an integral part of an institution's Occupational Health and Safety Program. If noise levels equal or exceed 85 dB, then a Hearing Conservation Program must be initiated in accordance with Occupational Safety and Health Administration standards. The tenets of a comprehensive Hearing Conservation Program are outlined.

Control of environmental factors, such as noise, in animal facilities is important to ensure that research animals respond consistently to experimental procedures and that experimental results are not confounded by outside influences. A survey of personnel involved with animal facilities (173 respondents) showed that almost all agreed with this statement. However, 48% thought that one or more environmental factors in their facilities could be stressing the animals, and a majority of respondents reported generation of audible noise from people (72% of respondents), fans (61%), and squeaky carts (56%). The presence of these noises was correlated with the perception of noise as a problem because of its psychologic and physiologic effects on the animals. The amount of time respondents spent in the facilities was strongly correlated with their perception of noise as a problem, with veterinarians spending the most time and perceiving the most problems, and professors and assistant/associate professors spending the least and perceiving the fewest. Therefore, they may lack key knowledge that can affect their research goals. In addition, because faculty are the least aware of noise as a potential problem but are primarily responsible for designing experiments, research involving animals may be confounded by noise as an unknown variable. This effect may lead to unnecessary numbers of animals being required to achieve statistical significance and possibly to erroneous interpretation of results. On the basis of the findings of this survey, we present recommendations for improving the environment, particularly for decreasing the noise level, in animal facilities.

Daily vacuuming of floors and flat-shelf racks is a standard procedure in our rodent housing rooms. To determine whether the noise produced by this activity is a potential stressor to animals used for transgenic and knockout mouse production, we measured the sound levels in our genetically engineered mouse facility under ambient conditions and at the in-cage and room levels during vacuuming. Spectral analysis showed that vacuuming produces a multitonal, low-frequency noise that is not attenuated by microisolation caging with bedding material. Comparison of cage-level spectral analysis results with age-specific audiograms of C57Bl/6 and CD1 mice showed that vacuuming produces frequencies audible to C57Bl/6 mice at 3 and 6 mo of age and to CD1 mice at 1 mo of age. These findings suggest that vacuuming in animal rooms could be a source of stress to animals with these genetic backgrounds.

Housing rats in an environment with high personnel activity increases microvascular leakiness to albumin in the mesenteric microcirculation and causes mast cell degranulation. In this study, rats were exposed to daily 15-min episodes of 90-dB SPL noise to determine whether similar effects occurred and whether vitamin E with α-lipoic acid or Traumeel (a homeopathic anti-inflammatory–analgesic) reduced these effects. Groups of rats fed a control diet (1000 IU/kg vitamin E) only, the control diet with Traumeel, or a diet with 10,000 IU/kg vitamin E and 1.65 g/kg lipoic acid were exposed to daily noise for 3 to 5 wk; a fourth group of rats, fed control diet, was housed with no excess noise. The rats were anesthetized, the superior mesenteric artery cannulated, and a portion of the microvasculature perfused for 1 min with fluoroscein isothiocyanate–albumin before fixing for microscopy. All groups exposed to excess noise had significantly more leaks per venule length and greater leak area per venule length than did the quiet group. However, the number and area of leaks in the rats that received Traumeel or vitamin E were significantly smaller than those in rats exposed to noise only. In addition, mast cell degranulation was significantly lower in rats given Traumeel. Thus exposure of rats to excessive noise produces structural damage in the mesenteric microvasculature that is significantly reduced by dietary supplements.

Is music just noise, and thus potentially harmful to laboratory animals, or can it have a beneficial effect? Research addressing this question has generated mixed results, perhaps because of the different types and styles of music used across various studies. The purpose of this study was to test the effects of 2 different types (vocal versus instrumental) and 2 genres (classical vocal versus 'easy-listening' vocal) of music on social behavior in 31 female and 26 male chimpanzees (Pan troglodytes). Results indicated that instrumental music was more effective at increasing affiliative behavior in both male and female chimpanzees, whereas vocal music was more effective at decreasing agonistic behavior. A comparison of 2 genre of vocal music indicated that easy-listening (slower tempo) vocal music was more effective at decreasing agonistic behavior in male chimpanzees than classical (faster tempo) vocal music. Agonistic behavior in females remained low (<0.5%) throughout the study and was unaffected by music. These results indicate that, like humans, captive chimpanzees react differently to various types and genres of music. The reactions varied depending on both the sex of the subject and the type of social behavior examined. Management programs should consider both type and genre when implementing a musical enrichment program for nonhuman primates.