Constitutive and Acquired Serotonin Deficiency Alters Memory and Hippocampal Synaptic Plasticity

Neuropsychopharmacology. 2017 Jan;42(2):512-523. doi: 10.1038/npp.2016.134. Epub 2016 Jul 27.

Abstract

Serotonin (5-HT) deficiency occurs in a number of brain disorders that affect cognitive function. However, a direct causal relationship between 5-HT hypo-transmission and memory and underlying mechanisms has not been established. We used mice with a constitutive depletion of 5-HT brain levels (Pet1KO mice) to analyze the contribution of 5-HT to different forms of learning and memory. Pet1KO mice exhibited a striking deficit in novel object recognition memory, a hippocampal-dependent task. No alterations were found in tasks for social recognition, procedural learning, or fear memory. Viral delivery of designer receptors exclusively activated by designer drugs was used to selectively silence the activity of 5-HT neurons in the raphe. Inhibition of 5-HT neurons in the median raphe, but not the dorsal raphe, was sufficient to impair object recognition in adult mice. In vivo electrophysiology in behaving mice showed that long-term potentiation in the hippocampus of 5-HT-deficient mice was altered, and administration of the 5-HT1A agonist 8-OHDPAT rescued the memory deficits. Our data suggest that hyposerotonergia selectively affects declarative hippocampal-dependent memory. Serotonergic projections from the median raphe are necessary to regulate object memory and hippocampal synaptic plasticity processes, through an inhibitory control mediated by 5-HT1A receptors.

MeSH terms

  • Animals
  • Excitatory Postsynaptic Potentials
  • Female
  • Hippocampus / physiology*
  • Long-Term Potentiation
  • Male
  • Memory / physiology*
  • Memory Consolidation / physiology
  • Mice, Knockout
  • Neuronal Plasticity*
  • Raphe Nuclei / physiology
  • Receptor, Serotonin, 5-HT1A / physiology
  • Recognition, Psychology / physiology
  • Serotonergic Neurons / physiology*
  • Serotonin / physiology*
  • Transcription Factors / genetics

Substances

  • Fev protein, mouse
  • Transcription Factors
  • Receptor, Serotonin, 5-HT1A
  • Serotonin