Effects of Stress and Hippocampal NMDA Receptor Antagonism on Recognition Memory in Rats

Abstract

Exposures to uncontrollable stress have been shown to alter ensuing synaptic plasticity in the hippocampus and interfere with hippocampal-dependent spatial memory in rats. The present study examined whether stress, which impairs hippocampal long-term potentiation (LTP), also affects (nonspatial) hippocampal-dependent object-recognition memory, as tested on the visual paired comparison task (VPC) in rats. After undergoing an inescapable restraint-tailshock stress experience, rats exhibited markedly impaired recognition memory at the 3-h (long) familiarization-to-test phase delay but not at the 5-min (short) delay. In contrast, unstressed control animals showed robust recognition memory (i.e., they exhibited reliable preferences for novel over familiar objects) at both short-and long-delay periods. The impairing effect of stress on long-delay recognition memory was transient because 48 h after undergoing stress experience, animals performed normally at the long delay. Similar to stress, microinfusions of DL-2-amino-5-phosphonovaleric acid (APV), a competitive N-methyl-D-aspartate receptor (NMDAR) antagonist that blocks LTP, into the dorsal hippocampus selectively impaired object-recognition memory at the long-delay period. Together, these results suggest that stress and intrahippocampal administration of APV affect recognition memory by influencing synaptic plasticity in the hippocampus.[The following individuals kindly provided reagents, samples, or unpublished information as indicated in the paper H. Blair.]

Behavioral deficits in sepsis-surviving rats induced by cecal ligation and perforation

“…These findings are relevant since the novel object recognition task in rodents is a nonspatial, nonaversive memory test, in contrast to our previous reports (21,22). In addition, the object recognition task has also been increasingly used as a powerful experimental tool to assess drug effects on memory and to investigate the neural mechanisms underlying learning and memory (24,25,(32)(33)(34)(35).…”

Metabolic and behavioral deficits following a routine surgical procedure in rats

“…Three way ANOVA for percent asymmetry with factors of Group, Brain Region and Time revealed a significant main effect for Group (F [1,264] = 154.96, P < 0.001) and Region (F [10,264] = 7.46, P < 0.001) but no main effect for Time (F [1,264] = 0.19, P = 0.657). A significant interaction occurred between Group and Brain Region (F [1,11] = 11.96, P < 0.001), where the most impacted regions were the primary motor cortex followed by the primary sensory and frontal cortices (F [3,11] =45.1, P<0.001). Two-way repeated measures analysis of percent asymmetry data from only cannulated animals that completed both scans were performed for each region, where factors were Group and Time.…”

“…Many cortical brain regions are pivotal to the formation of memories and brain plasticity [3,7,29] and intracranial surgery usually involves cortical regions even if the target is subcortical. For example, a surgical implant targeting the striatum passes through the motor and sensory cortices of the rat, and we have shown that these areas as well as distal cortical areas show a persistent metabolic decline long after the cannulation.…”

Environmental enrichment reduces the mnemonic and neural benefits of estrogen

“…A preference for the novel object during the choice phase was assessed using one-sample t-tests to determine whether time spent with the novel object differed significantly from the chance value of 15 s (Baker and Kim, 2002;Frick and Gresack, 2003). This type of t-test was used because time spent with the novel object is not independent from time spent with the familiar object, as the total time exploring must equal 30 s. For the same reason, one-sample t-tests were used to determine whether time spent with the northwest object during the sample phase differed significantly from 15 s.…”