The Guinea Pigs Deserve a Hearing
Many years ago I remember seeing in a physiology textbook two photographs
of a guinea pig’s inner ear, taken under a microscope before
and after exposure to destructively loud noise. The first image
showed the sensitive cochlear hairs arranged in neat rows; in the
second they looked like a stand of trees flattened by a violent
hurricane.
Unfortunately, such experiments are still being done today. A Boolean
search of “loud noise AND hearing loss” on the National
Institutes of Health’s PubMed database revealed about 35 animal
studies between 1976 and 2004, most of which involved exposing the
subjects to loud noise. Guinea pigs were the most often-used species
(20 studies), then cats (8), monkeys (2), and one each of mice,
chinchillas, pigeons, and lizards. A modified search would no doubt
turn up other studies.
Here’s a brief sampling from the animal protocols, spanning
two decades:
- Guinea pigs were exposed to loud pure tones. The effects on
their inner ear structure and function were assessed at different
times thereafter.1
- Blood flow to the inner ear was measured in 15 guinea pigs
using an implanted probe during delivery of sounds up to 120 dB
intensity.2
- The brains of 45 guinea pigs were electrically monitored during
exposure to loud noise. The animals were then killed and their
brain tissue analyzed for potential resistance to oxygen toxicity.3
The study of hearing loss and its treatment lends well to human
clinical methods, because human patients can verbally report their
hearing experiences to an experimenter. Here are three recent
examples of clinical studies turned up by my search:
- Three hearing aid circuits were compared for various parameters,
including overall sound quality, using 360 hearing-impaired human
volunteers.4
- Nine human patients with deafness in one ear were evaluated
for sound localization and speech perception, first with a conventional
hearing aid, then with a bone-anchored hearing aid (BAHA) implanted
in the deaf ear.5
- Male aircraft factory workers (n=94) were screened to examine
possible genotypic, demographic (age) and behavioral (smoking)
predispositions to noise-induced hearing loss (NIHL).6
Other clinical approaches included preventive studies, individual
case studies, and surgical interventions (including veterinary).
Overall, there appears to be little connection between the animal
and human research, and it’s unclear to what degree, if any,
the animal studies inform clinicians. One thing is certain: the
animal research—unlike the clinical—is not performed
to the benefit of its subjects.
It makes far more sense to try to prevent hearing loss through
public education. Several of the clinical studies I reviewed assessed
the effects of loud music on party-goers and concert-goers and the
failures of at-risk workers to deploy noise-protective equipment.
Convincing people at rock concerts to wear earplugs, for instance,
would be a good start.
References
1. Robertson D. Combined electrophysiology and ultrastructure of
acoustic trauma in the guinea pig cochlea. Arch Otorhinolaryngol.
1981;230(3):257-63.
2. Okamoto A, Hasegawa M, Tamura T, Homma T, Komatsuzaki A. Effects
of frequency and intensity of sound on cochlear blood flow. Acta
Otolaryngol. 1992;112(1):59-64.
3. Shupak A, Tal D, Pratt H, Sharoni Z, Hochman A. Attenuation of
cerebral oxygen toxicity by sound conditioning. Otol Neurotol. 2004
Mar;25(2):186-92.
4. Noffsinger D, Haskell GB, Larson VD, Williams DW, Wilson E, Plunkett
S, Kenworthy D. uality rating test of hearing aid benefit in the
NIDCD/VA Clinical Trial. Ear Hear. 2002 Aug;23(4):291-300.
5. Bosman AJ, Hol MK, Snik AF, Mylanus EA, Cremers CW. Bone-anchored
hearing aids in unilateral inner ear deafness. Acta Otolaryngol.
2003 Jan;123(2):258-60.
6. Fortunato G, Marciano E, Zarrilli F, Mazzaccara C, Intrieri M,
Calcagno G, Vitale DF, La Manna P, Saulino C, Marcelli V, Sacchetti
L. Paraoxonase and superoxide dismutase gene polymorphisms and noise-induced
hearing loss. Clin Chem. 2004 Nov;50(11):2012-8. Epub 2004 Sep 02.
Media
Center | Health | Research
| About PCRM | Catalog
| Join Us | Search
| Site Index | Home
The site does
not provide medical or legal advice. This Web site is for information purposes
only.
Full Disclaimer | Privacy Policy
|
Animal
Experimentation Issues 
