Divergent actions of serotonin receptor activation during fictive swimming in frog embryos

D. L. McLean, K. T. Sillar*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


We have investigated the pharmacology underlying locomotor system responses to serotonin (5-HT) in embryos of the frog, Rana temporaria, to provide a comparison to studies in embryos of its close relative, Xenopus laevis. Our findings suggest that two divergent mechanisms underlie the modulation of locomotion by 5-HT in Rana. Bath-applied 5-HT or 5-carboxamidotyptamine, a 5-HT1,5A,7 receptor agonist, can modulate fictive swimming in a dose-dependent manner, increasing burst durations and cycle periods. However, activation of 5-HT1,7 receptors with R8-OHDPAT or 8-OHDPAT fails to mimic 5-HT, and in some cases exerts exactly the opposite response; decreasing burst durations and cycle periods. Elevating endogenous 5-HT levels by blocking re-uptake with clomipramine transiently increases burst durations. The receptors involved in this endogenous response include 5-HT1A receptors, as in Xenopus, but also 5-HT7 receptors. However, like the 8-OHDPAT enantiomers, prolonged re-uptake inhibition can result in a motor response in the opposite direction to exogenous 5-HT. This effect is not reversed by 5-HT1A and/or 5-HT7 receptor antagonism, implicating 5-HT1B/1D receptors. Remarkably, antagonism of these receptors using methiothepin unmasks a dose-dependent response to clomipramine, reminiscent of exogenous 5-HT. Our data suggest that 5-HT1A,7 and 5-HT 1B/1D receptors act as gain-setters of burst durations, whilst 5-HT5A receptors are involved in the effects of bath-applied 5-HT on locomotion.

Original languageEnglish (US)
Pages (from-to)391-402
Number of pages12
JournalJournal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology
Issue number5
StatePublished - May 2004


  • 5-HT
  • Autoreceptors
  • Neuromodulation
  • Rana temporaria
  • Vertebrate locomotion

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Animal Science and Zoology
  • Behavioral Neuroscience


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