Serotonin and acetylcholine are crucial to maintain hippocampal synapses and memory acquisition in rats.

Treatment with serotonin and acetylcholine depletors reduced the number of synapses in the rat hippocampus. Animals that received the drug treatment lost a substantial number of synapses and showed an apparent impairment in memory acquisition. Although the animals were behaviorally impaired following the treatment, spatial memory was nonetheless eventually attained despite the disappearance of long-term potentiation. These data suggest that synapses in the hippocampus that are normally maintained by serotonin and acetylcholine are crucial for normal acquisition of spatial memory. The number of synapses maintained by biogenic amines may be a basic mechanism for neurobehavioral plasticity.