AN EXAMINATION OF THE RELATIONS BETWEEN HIPPOCAMPAL LONG-TERM POTENTIATION, KINDLING, AFTERDISCHARGE, AND PLACE LEARNING IN THE WATER MAZE

Two approaches were used to study the relations between the acquisitio n of place learning in the Morris water maze and long-term potentiatio n (LTP), kindling, and afterdischarge (AD). In the first, the possibil ity of behavioral LTP in the dentate gyrus field potential evoked by s timulation of the perforant path was evaluated in rats that showed rob ust place learning in the water maze. There was no effect of place lea rning on the field potential, and field potential measures did not cor relate with place learning acquisition measures. In the second approac h, the effect of bilateral saturation of LTP on subsequent place learn ing in the water maze task, begun within 5 minutes of the last LTP ses sion, was evaluated. The effect of kindled seizures evoked bilaterally from the perforant path, or of a single unilateral AD, on acquisition of the water maze task (begun within 10 minutes) were also evaluated. Bilateral LTP saturation did not affect place learning, and the bilat eral LTP group learned as readily as controls. In contrast, the kindle d and AD groups were severely impaired in their performance of the pla ce learning task. A second day of training in the water maze without a ny further electrical stimulation indicated that these groups had acqu ired considerable information on the first day of maze training and we re not distinguishable from controls on the second day of training. Th is indicated that the deficit in these groups on the first day of trai ning was temporary and likely resulted from a temporary perturbation o f normal brain function due to the seizures. The results indicate that bilateral saturation of LTP in the dentate gyrus does not affect plac e learning in the water maze. They also indicate that recent hippocamp al seizures, but not kindling, disrupt place learning in this task.