Animal Model for Tinnitus

Experimental equipment used in conducting tinnitus research with rats.

Tinnitus or "ringing in the ears" is a subjective experience that millions of people experience, and many people suffer greatly from tinnitus. In order to study the neural and physiological basis of tinnitus it is necessary the use animals. However, tinnitus is a subjective percept, so how does one know if an animal experiences tinnitus and if so if that experience is related to that perceived by humans? Dr. James Brennan, Dean of the Graduate School, Professor of Psychology and Adjunct Professor of Parmly, has developed a classical conditioning procedure using rats that indicates that under certain situations rats behave as if they are responding to sound even when no sound is present. An inference from this result is that the sound the rats are perceiving is a subjective experience like tinnitus. The behavior is elicited with administration of the compound, salicylate. Salicylate is the compound in aspirin which in large doses causes tinnitus in humans. In simple terms the rats are trained to stop drinking water whenever a sound is turned off for awhile. When rats are deprived of some water, they will drink water in the test chamber as long as a sound is present. They have been conditioned (by the delivery of mild shock) to stop licking when sound stops. Thus, rats put into a test cage without sound drink very little. If sound is turned on they start drinking. They also start drinking after they have been injected with the correct dose of salicylate, but not after injection with a placebo. Thus, the salicylate acts like sound in maintaining drinking. Dr. Brennan has shown that modulation of the calcium intake of the animal causes changes in the licking behavior following the salicylate injections. That is, calcium can sometimes cause the rats to stop drinking after the salicylate has caused them to drink. One can infer that the calcium might act to "block" the action of the salicylate in producing the tinnitus-like response in the rats. Since calcium is a major chemical in the maintenance of the nervous system, it is possible that some aspect of the chemical-calcium action of maintaining neural activity may be involved with the generation of tinnitus. This issue along with many others might be able to be addressed by this animal model of tinnitus.