Concurrent activation of hippocampal glycine and polyamine sites of the N-methyl-D-aspartate receptor synergistically reverses working memory deficits in rats.

Intrahippocampal administration of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (0.18 microg/side) significantly increased the number of errors in the working memory task with a three-panel runway setup. The increase in working memory errors by intrahippocampal MK-801 was significantly attenuated by concurrent infusion of D-cycloserine (1.0 microg/side) or spermidine (10 microg/side), agonists of the glycine and polyamine modulatory sites on the NMDA receptor/channel complex, respectively. Combined injection of the behaviorally ineffective doses of 0.1 microg/side D-cycloserine and 0.32 microg/side spermidine synergistically reduced intrahippocampal MK-801-induced increase in working memory errors. The combination of D-cycloserine and spermidine also synergistically attenuated the increase in working memory errors resulting from intrahippocampal injection of the muscarinic acetylcholine receptor antagonist scopolamine (3.2 microg/side). These results suggest that positive modulation of the NMDA receptor/channel through activation of the glycine and polyamine sites can synergistically compensate deficiency of hippocampal NMDA and muscarinic receptor-mediated neurotransmission involved in working memory function.