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  • Title: A paradoxical locomotor response in serotonin 5-HT(2C) receptor mutant mice.
    Author: Heisler LK, Tecott LH.
    Journal: J Neurosci; 2000 Apr 15; 20(8):RC71. PubMed ID: 10751458.
    Abstract:
    Paradoxical behavioral responses to nonselective neuropsychiatric drugs are frequently encountered and poorly understood. We report that a single receptor gene mutation produces a paradoxical response to the nonspecific serotonin receptor agonist m-chlorophenylpiperazine (mCPP). Although this compound normally suppresses locomotion, it produces hyperactivity in mice bearing a targeted mutation of the 5-HT(2C) receptor gene. This effect was blocked by pretreatment with a 5-HT(1B) receptor antagonist, indicating that the behavioral consequences of mCPP-induced 5-HT(1B) receptor stimulation are unmasked in animals devoid of 5-HT(2C) receptor function. Furthermore, this paradoxical response to mCPP was reproduced in wild-type C57BL/6 mice by previous pharmacological blockade of 5-HT(2C) receptors, indicating that the mutant phenotype does not result from perturbations of brain development. These effects of 5-HT1B and 5-HT(2C) receptor antagonists likely reflected blockade of pharmacological actions of mCPP, because these compounds did not alter locomotor activity levels when administered alone. Thus, mCPP interacts with distinct 5-HT receptor targets that produce opposing effects on locomotor activity levels. A paradoxical behavioral response is produced by the genetic inactivation of the target that produces the prevailing effect of the drug in the wild-type animal. This genetically based paradoxical drug effect provides a model for considering the effects of genetic load on neurobehavioral responses to drugs.
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