Salicylate-Induced Changes in Hearing Thresholds in Mongolian Gerbils Are Correlated With Tinnitus Frequency but Not With Tinnitus Strength.

Tinnitus is an auditory phantom percept without external sound sources. Despite the high prevalence and tinnitus-associated distress of affected patients, the pathophysiology of tinnitus remains largely unknown, making prevention and treatments difficult to develop. In order to elucidate the pathophysiology of tinnitus, animal models are used where tinnitus is induced either permanently by noise trauma or transiently by the application of salicylate. In a model of trauma-induced tinnitus, we have suggested a central origin of tinnitus-related development of neuronal hyperactivity based on stochastic resonance (SR). SR refers to the physiological phenomenon that weak subthreshold signals for given sensors (or synapses) can still be detected and transmitted if appropriate noise is added to the input of the sensor. The main objective of this study was to characterize the neurophysiological and behavioral effects during salicylate-induced tinnitus and compare these to the conditions within the trauma model. Our data show, in line with the pharmacokinetics, that hearing thresholds generally increase 2 h after salicylate injections. This increase was significantly stronger within the region of best hearing compared to other frequencies. Furthermore, animals showed behavioral signs of tinnitus during that time window and frequency range as assessed by gap prepulse inhibition of the acoustic startle reflex (GPIAS). In contrast to animals with noise trauma-induced tinnitus, salicylate-induced tinnitus animals showed no correlation between hearing thresholds and behavioral signs of tinnitus, indicating that the development of tinnitus after salicylate injection is not based on SR as proposed for the trauma model. In other words, salicylate-induced tinnitus and noise trauma-induced tinnitus are not based on the same neurophysiological mechanism.

Dietary Supplementation of Lion's Mane Medicinal Mushroom, Hericium erinaceus (Agaricomycetes), and Spatial Memory in Wild-Type Mice.

Hericium erinaceus is an edible and medicinal mushroom with potential neuroprotective effects. The study of H. erinaceus has attracted considerable attention during the past 10 years, particularly with regard to its potential utility in the treatment of motor dysfunction, Alzheimer disease, and other forms of dementia. We previously determined that oral supplementation with H. erinaceus results in significant improvements in novelty-seeking behavior and novel object recognition in mice. In this study, H. erinaceus was added to the diets of wild-type mice for 2 months, and effects on spatial memory were evaluated by means of a Y maze and an object location task. We found that H. erinaceus increased general locomotor activity but had no effect on spatial memory. Thus, oral supplementation with H. erinaceus yields specific and selective improvements in recognition memory without altering spatial working memory, which supports the hypothesis that recognition memory can be modeled as a dual process. In this model, the perirhinal cortex supports the recognition of individual items as part of a circuit involved in familiarity with an encountered stimulus, whereas the hippocampus supports recollected associations and relationships between stimuli.