COGNITIVE AND MNEMONIC DYSFUNCTIONS IN RATS WITH HIPPOCAMPAL-ENTORHINAL LESIONS - ATTENUATING EFFECTS OF GLYCINE INJECTIONS

Transections of the fiber connections between the temporal cortex (TC) and the lateral entorhinal cortex (LEC) result in decreased concentra tion of glutamate in TC and LEC, and also result in impaired memory. A dministration of glutamatergic agonists such as glycine restores mnemo nic function in rats with TC/LEC lesions. Because TC/LEC transections combined with damage to the predominantly glutamatergic hippocampus (H ipp) can severely impede both the acquisition and retention of a discr imination task, it appeared pertinent to examine the impact of glycine on rats with combined lesions. The results from Experiment 1 show tha t one injection of glycine made rats with Hipp + TC/LEC lesions indist inguishable from controls in acquiring and retaining the discriminatio n task. The complete restoration of functions may be associated with t he incomplete lesions used in the combination. To highlight this issue , rats with total hippocampal lesions were treated with the same proce dure (Experiment 2). The results show that glycine-treated rats displa yed only some improvement in learning the task. The findings are discu ssed in terms of the localization of mitigating processes and the pote ntial clinical relevance of agonists that enhance glutamatergic neurot ransmission.