Taurine Effects on Emotional Learning and Memory in Aged Mice: Neurochemical Alterations and Differentiation in Auditory Cued Fear and Context Conditioning

Abstract

Previously we have shown FVB/NJ mice given taurine acutely (i.e. 43 mg/kg/s.c. [aTau]) is anxiolytic, whereas chronically (0.05% w/v for >4 weeks [cTau]) produces anxiogenic phenotypes under select aversive behavioral experiments, but negated emotional contributions to acquisition learning and retention. Hyperexcitability induced in c-Tau mice is further exacerbated under stressful conditions compromising discrimination between cognitive vs. emotional learning. In the present study, we investigated differences between a-Tau and c-Tau mice using the auditory cued tone (ACTC) and context conditioning (CC) tests. Consistent with previous results, a-Tau mice exhibit less fear and increased inhibition, whereas c-Tau mice exhibit increased fear and decreased inhibition to ACTC and CC. Once fear conditioned, taurine mice become hypersensitive to novel environments and ACTC. Taurine brain levels are noted to increase in response to stressors as a neuroprotective mechanism against hyperexcitability. We suggest that c-Tau mice have increased accumulation of cysteamine (Cyst) and depleted somatostatin (SS) expression resulting in fear disregulation through GABAergic projection neurons in the limbic system, which are not seen in a-Tau mice. Our findings suggest that taurine causes not only varied phenotypic profiles of emotional fear learning, but are further complicated by the inability to associate cues with aversive stimuli due to potential auditory sensory overloading.