BUFFALO, N.Y. -- A novel rat behavioral model of tinnitus that
will allow researchers to study this debilitating condition in a
manner never before possible and to test potential treatments has
been developed by researchers with the University at Buffalo's
Center for Hearing & Deafness.
Center researchers, who have been studying tinnitus for more
than a decade, will use this animal model to monitor the activity
of individual neurons in the animals' brains where the phantom
sounds of tinnitus are thought to occur in a new study funded by a
$167,000 grant from the American Tinnitus Association.
The novel behavior paradigm, which involved training the animals
to abstain from drinking when they perceive sound, is described in
the April issue of Hearing Research.
"Having this animal model to work with and to observe will allow
us to make significant strides in identifying the underlying neural
mechanisms of this condition," said Richard Salvi, Ph.D., director
of the Center for Hearing & Deafness and primary researcher on
the new study. "We hope this research will bring us closer to
finding a treatment for tinnitus and to providing relief to the
millions who suffer from it.
"The neural mechanisms that give rise to the phantom sound of
tinnitus are not well understood because of the limited number of
animal models available to work with," continued Salvi, professor
in the Department of Communicative Disorders and Sciences in the UB
College of Arts and Sciences. "This new model gives us the ability
to have an animal make a behavioral response to tell us it hears
the phantom sound of tinnitus and to measure what is going on in
the brain at the same time. No one has been able to do this before
in a 'behaving' animal."
The model was developed by Edward Lobarinas, a doctoral student
in the UB Department of Communicative Disorders and Sciences and a
member of the center. The rats were trained to drink from their
water dispenser during periods of quiet, but to refrain from
drinking during actual noise, defined as "licks in sound."
Once this pattern was established, researchers injected each
animal with saline or a solution containing increasing
concentrations of sodium salicylate, or aspirin, which is known to
induce the phantom sounds of tinnitus. Each dose of aspirin -- 50,
100, 150 and 350 milligrams per kilogram of body weight (mg/kg) --
was given for two days. Doses were separated by a week to allow
behavior to return to baseline between treatments. Researchers
hypothesized that when trained animals sensed the phantom sound of
tinnitus during quiet periods, they would interpret it as "real
sound" and would refuse to drink.
Results showed that when animals received saline or the 50 mg/kg
aspirin solution, they drank during quiet as they were conditioned
to do, indicating no evidence of tinnitus. The 100 mg/kg dose
produced a slight suppression of licking during quiet. However, the
150 mg/kg and 350 mg/kg treatments almost completely suppressed
licking during the quiet interval, indicating the rats were hearing
a phantom sound. The high dose of sodium salicylate produced
behaviors in quiet that were similar to a real sound of 40
decibels, Salvi said.
"This cessation of licking during quiet would appear to indicate
the animals are sensing a phantom noise, the condition that defines
tinnitus, although no noise was present," said Lobarinas. "After
the salicylate treatment ended, the rats gradually returned to
their normal conditioned behavior in two-to-three days, indicating
the disappearance of tinnitus."
With the two-year grant from the American Tinnitus Association,
the researchers will monitor and correlate changes in neural
activity in the auditory cortex, a region of the brain responsible
for processing and interpreting sound, by taking readings from
individual neurons before, during and after inducing tinnitus.
"We expect to see that a subpopulation of neurons in the
auditory cortex will increase their activity when the rats
experience tinnitus and that the activity will decrease when the
tinnitus disappears," said Salvi.
Additional researchers on the project to develop an animal
behavioral model of tinnitus were Wei Sun, research assistant
professor, and Ross Cushing, AuD, both in the UB Department of
Communicative Disorders and Sciences.
Their research was supported in part by grants from the National
Institute on Deafness and Other Communication Disorders and the
Royal National Institute for Deaf People.
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public university, the largest and most comprehensive campus in the
State University of New York.