The impact of high-frequency stimulation of the hippocampal Schaffer collateral pathway on the consolidation of spatial memory in male laboratory rats

The acquisition and consolidation of new tasks into long-term memory involve the appearance of sharp-wave ripples in the temporal lobe during resting or sleep, which play a crucial role in memory consolidation. Additionally, sharp-wave ripples, high-frequency waves in the molecular layer of the hippocampus, are associated with synaptic plasticity and memory consolidation. This study aims to investigate the impact of high-frequency electrical stimulation of the hippocampal Schaffer collateral (SC) pathway on memory consolidation in behaving rats.

Stereotaxic surgery was conducted to implant stimulating electrodes in the SC pathway and recording electrodes in the CA1 region of male Wistar rats. After confirming electrophysiological recording, electrodes were secured to the skull using dental cement. Two hours following each acquisition session rats underwent stimulation of the SC pathway with a frequency of 200 Hz to assess its effect on spatial memory formation. Spatial learning was then conducted using the Morris water maze over three consecutive days. Electrical stimulation occurred two hours post-learning on each day, and spatial memory was evaluated on the fourth day.

Stimulation of the SC pathway with high frequency resulted in long-term synaptic strengthening in CA1. However, behavioral testing revealed no significant difference in learning and spatial memory between the group receiving electrical stimulation and the control group.

These findings suggest that high-frequency stimulation of the SC pathway does not enhance memory, indicating that synaptic strengthening in the CA1 region does not necessarily translate into memory improvement.