Abstract
This study examined the role of the serotonin 5-HT2 receptor in motor function by examining the effect of antagonists on the motor performance of a cranial nerve reflex, the nictitating membrane (NM) reflex of the rabbit. The NM reflex was elicited by varying intensities of a tactile stimulus and the magnitudes of the elicited responses were measured at each intensity. Dose-response curves were obtained for the effects of several 5-HT2 receptor antagonists on response magnitude. d-Bromolysergic acid diethylamide (BOL), LY-53,857 and ketanserin had no significant effect on the magnitude of the NM reflex, indicating that they are neutral antagonists. However, the 5-HT2 receptor antagonists ritanserin, MDL-11,939 and mianserin produced a significant reduction in response magnitude with no significant effects on response frequency, suggesting that they were acting as inverse agonists at the 5-HT2 receptor. The reduction in reflex magnitude produced by mianserin (10 µmol/kg) was fully blocked by BOL (5.8 µmol/kg), supporting the conclusion that mianserin was producing a reduction in reflex magnitude through an effect at the 5-HT2 receptor. The occurrence of inverse agonism suggests the possible existence of constitutive activity in vivo. We conclude that the 5-HT2 receptor (either 2A or 2C) plays an important role in motor function, perhaps by providing a tonic influence on motor systems.
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Received: 12 February 1998 / Final version: 2 July 1998
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Harvey, J., Welsh, S., Hood, H. et al. Effect of 5-HT2 receptor antagonists on a cranial nerve reflex in the rabbit: evidence for inverse agonism. Psychopharmacology 141, 162–168 (1999). https://doi.org/10.1007/s002130050820
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DOI: https://doi.org/10.1007/s002130050820