Effect of Circadian Phase on Performance of Rats in the Morris Water Maze Task

Abstract

The authors examined spatial working memory in the Morris water maze during the activity and rest periods of Wistar rats. Wheel-running activity was measured continuously as a marker of circadian phase. To minimize possible masking effects on performance, animals were placed in constant dim light the day before testing and tested in similar light conditions. Three experiments were run, each of them using animals varying in their previous experience in the water maze. Half of the animals of each experiment were tested 2 to 3 h after activity onset (active group), and the other half were tested 14 to 15 h after activity onset (inactive group). In the three experiments, a significant phase effect was observed in the animals' performance in the water maze; animals tested in the active phase showed steeper acquisition curves. These phase effects on performance are due to the animals' search pattern and not to a better acquisition and maintenance of spatial information; rats tested in the inactive phase found the platform faster on the first trial of the test, when the information on the location of the platform had not been presented to the animals. This effect vanished as the amount of training in the pool increased. Finally, swimming speed also showed a temporal effect, suggesting the existence of a phase effect for motivation to escape from the water; rats tested during their inactive phase tended to swim faster. All together, the data suggest a modulating effect of the biological clock on performance in the water maze, particularly when the animals are less experienced.

The Circadian Clock Modulates Core Steps in Long-Term Memory Formation inAplysia

“…In mice, the circadian clock modulates contextual fear conditioning and hippocampal long-term potentiation (Valentinuzzi et al, 2001;Chaudhury and Colwell, 2002;Chaudhury et al, 2005). Some circadian modulation of memory also has been observed in rats (Valentinuzzi et al, 2004). Despite the behavioral evidence for circadian modulation of memory, little molecular evidence exists demonstrating an interaction between the circadian oscillator and downstream targets involved in memory formation.…”

Circadian regulation of insect olfactory learning

“…In some instances, the circadian phase may function as a context for learning (time stamping) so that recall and performance are better at 24-h intervals after learning (1)(2)(3)(4). In other cases, performance may be modulated by the circadian phase independent of the phase of learning (5), and there have been several recent reports that memory acquisition or consolidation may depend on the circadian phase of training in mollusks (6)(7)(8), rodents (9,10), and humans (11). Finally, there have been reports that disruption of the circadian system by phase shifting (jet lag) can impair memory (12,13).…”

Synchrony and desynchrony in circadian clocks: impacts on learning and memory

“…In rodents, acquisition of hippocampal-dependent learning paradigms such as Morris water maze, contextual fear conditioning, and the radial arm maze, is higher during the night (Hauber and Bareiss 2001;Valentinuzzi et al 2001Valentinuzzi et al , 2004. Similarly in hippocampal long-term potentiation, the amplitude of population spikes is significantly greater during the night .…”