Is waning of a 5-hydroxytryptamine (5-HT)-mediated syndrome due to 5-HT2 receptor down-regulation?

The 5-hydroxytryptamine (5-HT) uptake inhibitor, paroxetine (11.6 mg/kg i.p.), given to rats pretreated with the monoamine oxidase inhibitor, phenelzine, 18 h (46.8 mg/kg i.p.) and 90 min (11.7 mg/kg i.p.) before, evoked a 5-HT-dependent syndrome which included wet-dog shakes (WDS). The frequency of WDS declined over the ensuing 3 h, at which time cortical 5-HT2 receptors showed a significant (30%) decrease in number. A second injection of paroxetine given at this time did not evoke a significant increase in the number of WDS, suggesting that spinal 5HT2 receptors might also have been down-regulated at the same time.