Late-term moderate prenatal alcohol exposure impairs tactile, but not spatial, discrimination in a T-maze continuous performance task in juvenile rats

Abstract

Existing maze apparatuses used in rodents often exclusively assess spatial discriminability as a means to evaluate learning impairments. Spatial learning in such paradigms is reportedly spared by moderate prenatal alcohol exposure in rats, suggesting that spatial reinforcement alone is insufficient to delineate executive dysfunction, which consistently manifests in humans prenatally-exposed to alcohol. To address this, we designed a single-session continuous performance task in the T-maze apparatus that requires rats to discriminate within and between simultaneously-presented spatial (left or right) and tactile (sandpaper or smooth) stimuli for food reinforcement across four sequential discrimination stages: simple discrimination, intradimensional reversal 1, extradimensional shift, and intradimensional reversal 2. This design incorporates elements of working memory, attention, and goal-seeking behavior which collectively contribute to the executive function construct. Here, we found that rats prenatally-exposed to alcohol performed worse in both the tactile intradimensional reversal and extradimensional shift; alternatively, rats prenatally-exposed to alcohol acquired the extradimensional shift faster when shifting from the tactile to spatial dimension. In line with previous work, moderate prenatal alcohol exposure spared specifically spatial discrimination in this paradigm. However, when tactile stimuli were mapped into the spatial dimension, rats prenatally-exposed to alcohol required more trials to discriminate between the dimensions. We demonstrate that tactile stimuli can be operantly employed in a continuous performance T-maze task to detect discriminatory learning impairments in rats exposed to moderate prenatal alcohol. The current paradigm may be useful for assessing features of executive dysfunction in rodent models of fetal alcohol spectrum disorders.