Abstract
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-HT1B/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 language | English |
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Pages (from-to) | 391-402 |
Number of pages | 12 |
Journal | Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology |
Volume | 190 |
DOIs | |
Publication status | Published - May 2004 |
Keywords
- 5-HT
- autoreceptors
- neuromodulation Rana temporaria
- vertebrate locomotion
- XENOPUS-LAEVIS TADPOLES
- RANA-TEMPORARIA EMBRYOS
- DEPENDENT POTASSIUM CHANNELS
- SPINAL-CORD
- LOCOMOTOR PATTERN
- POSTEMBRYONIC DEVELOPMENT
- POSTNATAL-DEVELOPMENT
- SYNAPTIC DRIVE
- 5-HT7 RECEPTOR
- MOTOR PATTERN