Dorsal hippocampal CA1 NMDA receptors mediate the interactive effects of quetiapine and lithium on memory retention in male rats

Lithium and quetiapine are administered simultaneously as a treatment for bipolar disorder. The concurrent use of these two drugs has been observed to affect the neurobiological mechanisms underlying learning and memory. To clarify the precise mechanisms involved, we evaluated the possible role of the dorsal hippocampal CA1 NMDA receptors in the interactive effects of lithium and quetiapine in memory consolidation.  The dorsal hippocampal CA1 regions of adult male Wistar rats were bilaterally cannulated, and a single-trial step-through inhibitory avoidance apparatus was used to assess memory consolidation.  Post-training administration of certain doses of lithium (20, 30, and 40 mg/kg, IP) diminished memory consolidation. Post-training administration of higher doses of quetiapine (5, 10, and 20 mg/kg, IP) augmented memory consolidation. Post-training administration of certain doses of quetiapine (2.5, 5, 10, and 20 mg/kg) dose-dependently restored lithium-induced memory impairment. Post-training microinjection of ineffective doses of the NMDA (10-5 and 10-4 µg/rat, intra-CA1) plus an ineffective dose of quetiapine (2.5 mg/kg) restored the lithium-induced memory impairment. Post-training microinjection of ineffective doses of the noncompetitive NMDA receptor antagonist, MK-801 (0.0625 and 0.0125 μg/rat, intra-CA1), diminished the quetiapine-induced (10 mg/kg) memory improvement in lithium-induced memory impairment. These findings suggest a functional interaction between lithium and quetiapine through hippocampal CA1 NMDA receptor mechanisms in memory consolidation.