Lateralized fascia dentata lesion and blockade of one hippocampus: Effect on spatial memory in rats

Unilateral blockade of the dorsal hippocampus by tetrodotoxin makes it poss ible to form lateralized spatial memories, which rapidly transfer to the na ive hippocampus when training continues with intact brain. Unilateral X-ray irradiation of newborn rats causes irreversible destruction of granule cel ls in the ipsilateral fascia dentata (FD). Possible compensation of poor te aming in the lesioned hemisphere by commissural transfer of memories from t he intact hippocampus was examined in seven rats with unilateral FD lesion, which were first trained in the Morris water maze to asymptotic performanc e (mean escape latency 6 +/- 1 s). Subsequent testing during functional abl ation either of the intact or of the lesioned hippocampus by tetrodotoxin r evealed escape latencies 35 +/- 8 s or 8 +/- 1 s, respectively. Probe trial tests during inactivation of the intact and lesioned hippocampus showed ta rget quadrant preference of 32 +/- 2% or 54 +/- 3%, respectively. The resul ts indicate: (a) that one intact hippocampus alone can support the water ma ze task, (b) that no, or only a very weak, memory trace is available in the lesioned hippocampus. It is concluded that the above results are due to th e inability of the FD lesioned hippocampus to process the information recei ved from the ipsilateral entorhinal cortex. Hippocampus 1998;8:647-650. (C) 1998 Wiley-Liss, Inc.