Journal of Neuroscience, Vol 13, 1759-1766, Copyright © 1993 by Society for Neuroscience
Extended temporal gradient for the retrograde and anterograde amnesia produced by ibotenate entorhinal cortex lesions in mice
YH Cho, D Beracochea and R Jaffard
Laboratoire de Neurosciences Comportementales et Cognitives, CNRS URA 339, Universite de Bordeaux I, Talence, France.
Effects of ibotenic entorhinal cortex (EC) lesions on both retrograde and
anterograde amnesia in mice were assessed using two-choice discrimination
tasks learned at different intervals before surgery in two eight-arm radial
mazes. The results indicated that EC-lesioned mice were severely impaired
in postoperative retention of discrimination problems learned 3 d or 2
weeks prior to surgery, but showed no deficit on problems learned between
4, and up to 6 weeks before surgery, as compared to sham-operated controls.
When trained on a novel two-choice discrimination problem (not acquired
preoperatively), experimental subjects demonstrated quite normal rates of
acquisition, but were impaired in learning its reversal. Furthermore, they
exhibited a faster rate of forgetting (anterograde amnesia) relative to
controls over a 2- week retention interval. These results indicate that
approximately 4 weeks is required before memory for a two-choice spatial
discrimination problem no longer depends on the integrity of the entorhinal
cortex, and suggests that, beyond this time, an EC-independent memory
storage system is capable of supporting the retrieval of information. The
data, together with complementary behavioral results, are discussed in the
context of current theories of memory storage.