Receptor mediation of exaggerated responses to serotonin-enhancing drugs in serotonin transporter (SERT)-deficient mice

Meredith A. Fox, Catherine L. Jensen, Pamela S. Gallagher, Dennis L. Murphy

Research output: Contribution to journalArticlepeer-review

58 Scopus citations


Administration of serotonin-enhancing drugs induces a distinctive behavioral syndrome in rodents. We previously reported that mice with a targeted disruption of the serotonin transporter (SERT) display some of these behaviors spontaneously, in the absence of drug. In the current studies, we assessed the drug-induced serotonin syndrome in SERT wildtype (+/+), heterozygous (+/-) and knockout (-/-) mice. In SERT -/- mice, the monoamine oxidase inhibitor (MAOI) tranylcypromine (1 mg/kg) or the serotonin precursor 5-hydroxy-l-tryptophan (5-HTP; 80 mg/kg) led to markedly exaggerated serotonin syndrome behaviors relative to SERT +/+ mice, with an intermediate phenotype in SERT +/- mice. SERT +/+ mice developed significant serotonin syndrome behaviors only with the combination of the MAO-A/B inhibitor tranylcypromine (0.5 or 1 mg/kg) or the MAO-A-selective inhibitor clorgyline (1.2 mg/kg) plus 5-HTP. In evaluations of underlying mechanisms, pretreatment with the Htr1a receptor antagonist WAY 100635 (1 mg/kg), but not the Htr7 antagonist SB 269970 (3 mg/kg) or the Htr2a antagonist MDL 11,939 (5 mg/kg), markedly decreased the exaggerated 5-HTP-induced behaviors in SERT -/- mice. Subsequent experiments showed that the Htr1a agonist 8-OH-DPAT (1 or 2 mg/kg) elicited serotonin syndrome behaviors in a dose-dependent manner, blocked by WAY 100635 (1 mg/kg), in mice of all three genotypes, confirming the role of Htr1a receptors. The current data document markedly enhanced behavioral sensitivity to serotonin-enhancing drugs in SERT-deficient mice. These studies also show that the exaggerated behavioral responses observed in SERT +/- and -/- mice are mediated by postsynaptic Htr1a receptors, and suggest intact postsynaptic Htr1a function in SERT -/- mice.

Original languageEnglish (US)
Pages (from-to)643-656
Number of pages14
Issue number5
StatePublished - Oct 2007
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Cellular and Molecular Neuroscience
  • Pharmacology


  • 5-Hydroxy-l-tryptophan (5-HTP)
  • Serotonin 1a receptors (5-HT1A, Htr1a)
  • Serotonin 2a receptors (5-HT2A, Htr2a)
  • Serotonin 7 receptors (5-HT7, Htr7)
  • Serotonin syndrome
  • Serotonin transporter (SERT) knockout mice


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