Inhibition of short-term memory formation in the chick by blockade of extracellular glutamate uptake

Injection of monosodium glutamate (40 nmol/hemisphere) into the intermediate hyperstriatum ventrale of the day-old chick inhibits the formation of short-term memory for a single trial learning that discriminates between colours of beads. These experiments showed that an excess of glutamate close to learning could be damaging to memory. In the present experiments we have blocked the normal reuptake of glutamate and suggest that glutamate release plays a role in normal learning. Removal of glutamate, released from presynaptic neurones during learning, is achieved by various neuronal and astrocytic glutamate transporters. By blocking the primarily astrocytic removal of glutamate by the injection of L-aspartic acid beta-hydroxamate, we effectively increased extrasynaptic levels of glutamate and inhibited short-term memory in a similar manner to central injection of 40 nmol glutamate per hemisphere. These experiments suggest that glutamate release within 2.5 min of the learning experience is an important feature of short-term memory formation. (C) 2003 Elsevier Inc. All rights reserved.