Astrocytes and interneurons in memory processing in the chick hippocampus: roles for G-coupled protein receptors, GABA(B) and mGluR1.

Glutamate and GABA acting at mGluR1 and GABA(B) receptors, respectively, have roles in memory processing in the hippocampus up to 35 min after bead discrimination learning in the young chick. Activation of mGluR1 receptors is important at 2.5 and 30 min after training, but modulation of these receptors between these two times has no effect on memory. This timing is similar to the action of glutamate on NMDA receptors. The GABA(B) antagonist, phaclofen, and the inhibitor of astrocytic oxidative metabolism, fluoroacetate, inhibited memory when injected between 2.5 and 30 min. Paradoxically, a high dose of the GABA(B) agonist, baclofen, also inhibited memory, but a low dose promoted memory consolidation--an effect possibly caused by too much information and loss of the 'message'. These results are interpreted in terms interactions between interneurons, astrocytes and pyramidal cells and demonstrate the importance of all cell types in memory processing in the hippocampus.