Impaired, spared, and enhanced ACh efflux across the hippocampus and striatum in diencephalic amnesia is dependent on task demands

Abstract

Diencephalic amnesia manifests itself through a host of neurological and memory impairments. A commonly employed animal model of diencephalic amnesia, pyrithiamine-induced thiamine deficiency (PTD), results in brain lesions and impairments similar in nature and distribution to those observed in humans with Wernicke–Korsakoff syndrome (WKS). In the current investigation, 2 separate experiments were conducted in which acetylcholine (ACh) efflux was assessed in the hippocampus and striatum of PTD-treated and pair-fed (PF) control male Sprague–Dawley rats. The goal was to determine under what behavioral conditions and in which brain structures ACh efflux was spared, impaired, or adaptively enhanced. In Experiment 1, rats were assessed on a spontaneous alternation task; in Experiment 2, rats were tested on a T-maze discrimination task that could be learned via a hippocampal- or striatal-based strategy. In Experiment 1, PTD-treated rats were impaired on the spontaneous alternation task and ACh efflux in the hippocampus during testing was significantly reduced, but spared in the striatum. In Experiment 2, PTD- and PF-treated rats did not differ in the number of trials to criterion, but PTD-treated rats demonstrated greater reliance upon egocentric cues to solve the task. Furthermore, ACh efflux in the striatum was greater during maze learning in the PTD-treated animals when compared to the PF animals. These results suggest that there is behavioral and systems level plasticity that can facilitate the use of alternative strategies to solve a task following diencephalic damage and WKS.