The Hidden Effects of Noise on Lab Animals

By: Tara Gandhi

Turner, Jeremy G, et al. “Hearing in Laboratory Animals: Strain Differences and Nonauditory Effects of Noise.” Comparative Medicine, vol. 55, no. 1, Feb. 2005, p. 12, pmc.ncbi.nlm.nih.gov/articles/PMC3725606/.

A lab animal in a petri dish, under the conditions of a trial. This Image was made with AI, and does not represent the research paper/experiment in any way

Introduction:

This article aims to investigate the causes of noise in laboratory environments, along with its effects on laboratory animals. The treatment and welfare of lab animals has been a cause for concern for a multitude of reasons, from a lack of safety to mental distress caused by experimentation and questionable experimentation methods as well. However, one of the most overlooked factors in the lives of lab animals is what they hear. Humans and animals have vastly different auditory ranges. Humans can hear sounds from a range of 20 Hz to 20,000 Hz. On the other hand, the auditory ranges of animals such as mice can extend as high as 90,000 Hz. Experimenters often overlook the impact of environmental noises, produced by both humans and animals, on laboratory animals, as many of these sounds fall beyond the range of human hearing. 

Nevertheless, it is essential to note that prolonged exposure to a wide range of noises can negatively impact lab animals in several ways, including developmental issues, permanent damage, and in severe cases, even death.

Causes of environmental noise:

First, let's explore the different sources of noise in laboratories. Technical devices (air conditioners, air handlers, ventilated racks) and various electronic devices (computers, phones, et cetera) and scientific instruments like MRI machines all produce sounds that humans can hear. However, these don't affect us as much, compared to animals like rats, which are impacted due to their small size and vast hearing range. As they possess the ability to pick up on ultrasonic sounds (sound waves with frequencies higher than 20,000 Hz), an activity as simple as snapping a wire-top cage lid to a plastic shoebox cage can produce an intense noise of nearly 100 dB (dB is the unit in which sound is measured) at frequencies up to 40 kHz. Moreover, other human activities, such as the opening and closing of doors, pushing carts, and even talking, can have severe repercussions on animals. The animals themselves also contribute to the sounds by climbing, chewing, rattling cages, and their vocalisations. This seems like a noisy enough environment already, but the design of the facilities, which feature concrete and epoxy surfaces, amplifies noise, increasing the reverberation of even the tiniest sounds. 

Auditory Effects of Noise Exposure

The effects of these intense noise exposures can damage the cochlea (spiral shaped organ in the inner ear, responsible for hearing) and inner ear of animals , leading to various adverse effects, such as Temporary Threshold Shift (TTS), which is a reversible form of hearing loss after prolonged exposure to volumes over 85dB. However, more severe cases can lead to Permanent threshold shift (PTS), which is irreversible damage that occurs with exposure to sounds exceeding 100 dB.  Susceptibility to TTS and PTS depends on the health, and species of an animal, however mammals are more prone to it due to their sophisticated auditory system.Moreover, prolonged exposure to loud noises can lead to partial deafness, which can weaken the sensory input that reaches the brain, altering the excitation cycles (the firing of neurons/sending of messages) and the control over the animal’s brain activity. As a result, with less auditory input, the brains of the animals may compensate by creating too much or too little noise in the head, which manifests as Hyperacusis (a condition where ordinary sounds are painfully loud) and Tinnitus (the perception of a buzzing sound when none is present). 

Furthermore, rats, mice, guinea pigs, and hamsters are observed to experience a phenomenon known as audiogenic, or noise-induced, seizures. These seizures are triggered by sudden, sharp sounds like jingling keys and can lead to a higher mortality rate, rewiring of the brain to have a lower threshold for future seizures, and may also impair the cognitive ability of the animals. Additionally, if lab animals are exposed to brief, loud noises during the critical early periods of their life, their susceptibility to seizures will increase. For example, a strain of lab mice, when exposed to 123dB of sound for 2 minutes, for a period of 2-3 weeks, had a 75% chance of experiencing seizures and death when exposed again later, showing the fatal impact of loud noises on animals.  

Non-Auditory Effects:

Apart from auditory and neural effects, excessive exposure to noise in lab animals can also affect multiple organ systems by activating the autonomic nervous system (a part of the nervous system that controls automatic, unconscious body functions) and the hypothalamic–pituitary–adrenal axis (a stress response system). 

It also has cardiovascular repercussions, such as increased heart rate and Vasoconstriction (narrowing of blood vessels), which  in the long term, causes hypertension (constant high blood pressure). Additionally, it can lead to increased levels of Norepinephrine, Cortisol, and Corticosterone, (stress hormones), potentially causing diseases and leading to elevated stress levels in the future. 

Lastly, it can affect pregnant animals by increasing the fetal mortality rate and even leading to offspring with poor learning abilities. Overall, it can also slow healing and mask animal communication, altering social behaviour. 

Solutions:

To combat this, experts suggest considering the species and strain of animals used in labs, and accordingly adjusting the frequencies, vibrations and intensity of sound in the environment. It is also recommended to separate nosy and quiet animals, along with minimising unnecessary noise, and the ultrasonic frequencies in the lab. 

Conclusions:

In conclusion, auditory strains in laboratory environments are a pressing issue that affects nearly every aspect of the animal's body, from its brain to its heart and especially their auditory system. It is an often-overlooked and detrimental aspect of their health. Controlling sound levels and frequencies is the way forward to minimise harm to laboratory animals and to make a significant contribution to biomedical research. 

Additional Sources:

1. Bosco, Francesca, et al. “Audiogenic Epileptic DBA/2 Mice Strain as a Model of Genetic Reflex Seizures and SUDEP.” Frontiers in Neurology, vol. 14, 23 Aug. 2023, www.ncbi.nlm.nih.gov/pmc/articles/PMC10481168/, https://doi.org/10.3389/fneur.2023.1223074.

2. Ryan, Allen F., et al. “Temporary and Permanent Noise-Induced Threshold Shifts.” Otology & Neurotology, vol. 37, no. 8, Sept. 2016, pp. 271–275, www.ncbi.nlm.nih.gov/pmc/articles/PMC4988324/, https://doi.org/10.1097/mao.0000000000001071.

3. Ventola, C Lee. “The Antibiotic Resistance Crisis: Part 1: Causes and Threats.” Pharmacy and Therapeutics, vol. 40, no. 4, Apr. 2015, p. 277, pmc.ncbi.nlm.nih.gov/articles/PMC4378521/.