Restoration of mnemonic function in rats with glutamergic temporal systems disrupted: dose and time of glycine injections.

Disruption of the connections between the temporal cortex (TC) and lateral entorhinal cortex (LEC) in rats causes impaired memory accompanied by decreased levels of glutamate in these neocortical areas. Administration of glutamergic agonists to rats with TC/LEC disruptions improves retroactive memory. The purpose of this study was to test effects of glycine on proactive memory. The results show that a relatively large dose of glycine (750 mg/kg) injected just prior to training enhanced both acquisition and retention of a discrimination task in TC/LEC rats. Glycine given 1 day prior to training impaired the initial phase of acquisition but improved retention (Experiment 1). Injection of glycine immediately following training or just prior to retrieval reinstated normal mnemonic function in TC/LEC animals, whereas glycine given midway between learning and retention had no such effect (Experiment 2). A potential mnemonic model function of TC/LEC lesion is suggested, and possible beneficial effects of glycine on patients with Alzheimer's disease are discussed.