Abstract
We have studied the influence of pre-training psychological stress on the expression of c-fos mRNA following long-term spatial memory retrieval. Rats were trained to learn the location of a hidden escape platform in the radial-arm water maze, and then their memory for the platform location was assessed 24 h later. Rat brains were extracted 30 min after the 24-h memory test trial for analysis of c-fos mRNA. Four groups were tested: (1) Rats given standard training (Standard); (2) Rats given cat exposure (Predator Stress) 30 min prior to training (Pre-Training Stress); (3) Rats given water exposure only (Water Yoked); and (4) Rats given no water exposure (Home Cage). The Standard trained group exhibited excellent 24 h memory which was accompanied by increased c-fos mRNA in the dorsal hippocampus and basolateral amygdala (BLA). The Water Yoked group exhibited no increase in c-fos mRNA in any brain region. Rats in the Pre-Training Stress group were classified into two subgroups: good and bad memory performers. Neither of the two Pre-Training Stress subgroups exhibited a significant change in c-fos mRNA expression in the dorsal hippocampus or BLA. Instead, stressed rats with good memory exhibited significantly greater c-fos mRNA expression in the dorsolateral striatum (DLS) compared to stressed rats with bad memory. This finding suggests that stressed rats with good memory used their DLS to generate a non-spatial (cue-based) strategy to learn and subsequently retrieve the memory of the platform location. Collectively, these findings provide evidence at a molecular level for the involvement of the hippocampus and BLA in the retrieval of spatial memory and contribute novel observations on the influence of pre-training stress in activating the DLS in response to long-term memory retrieval.
Highlights
A major goal in the study of the neurobiology of memory is to determine aspects of neural activity that are associated with different components of cognitive processes, such as the acquisition, consolidation, and retrieval phases of memory processing
We have studied the expression of c-fos mRNA associated with long-term spatial memory retrieval in rats administered water maze training under control conditions, and in rats which had been stressed before training began
This putative stress-induced shift to a non-hippocampal brain memory system, such as the dorsolateral striatum (DLS), may have enabled a subset of the stressed rats to remember the location of the hidden platform, despite their exhibiting a lack of increased c-fos mRNA transcription in their hippocampus and basolateral amygdala (BLA) at the time of memory retrieval
Summary
A major goal in the study of the neurobiology of memory is to determine aspects of neural activity that are associated with different components of cognitive processes, such as the acquisition, consolidation, and retrieval phases of memory processing. Much of the research linking neuroplasticity to memory has focused on the hippocampus (Szapiro et al, 2002; Miyamoto, 2006; Bekinschtein et al, 2008). In rodents, this temporal lobe structure plays a critical role in spatial learning and memory (Morris et al, 1982, 1986; Guzowski and McGaugh, 1997; Kesner et al, 2004; Martin and Clark, 2007; Bird and Burgess, 2008). Most of the work has focused on the necessary role of the hippocampus in memory formation, research has demonstrated an involvement of the rodent (Riedel et al, 1999; Corcoran and Maren, 2001; Jezek et al, 2002; Szapiro et al, 2002; Micheau et al, 2004; Sutherland et al, 2010) and human (Dolan and Fletcher, 1999; Bosshardt et al, 2005; Rekkas and Constable, 2005; Moscovitch et al, 2006; Cabeza and St Jacques, 2007; Nadel et al, 2007; Spiers and Maguire, 2007a,b) hippocampus in long-term memory retrieval
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