Like melatonin, agomelatine (S20098) increases the amplitude of oscillations of two clock outputs: melatonin and temperature rhythms.

Depression and biological rhythms disturbances are strongly associated. Agomelatine is an antidepressant with melatoninergic MT1-MT2 agonist and serotoninergic 5-HT2c antagonist properties. Both melatonin and 5-HT are known to modulate circadian rhythmicity controlled by the endogenous clock located in the suprachiasmatic nuclei (SCN). The aim of the present study was to compare the effect of an acute injection of agomelatine (Ago), melatonin (MLT) or an antagonist 5-HT2c (S32006), on the rhythms of two robust clock outputs: the pineal MLT secretion and the body temperature rhythm (Tc). Daily endogenous MLT profiles were measured using transpineal microdialysis over 4 consecutive days in rats maintained on a 12 h light/12 h dark cycle. Simultaneously, Tc was recorded. The drugs were injected subcutaneously at three doses (1, 2.5 or 5 mg/kg) at the onset of darkness. Both Ago and MLT, at the dose of 2.5 mg/kg, increased the amplitude of the peak of MLT secretion and this effect was observed 2 d after injection. Moreover, both drugs induced a dose-dependent advance of the rhythm onset which resulted in lengthening of the MLT peak. S32006 had no effect on the rhythm of MLT. Ago, MLT and S32006 increased the amplitude of the rhythm of Tc. These data suggest a central action of Ago, directly on the SCN, via melatoninergic receptors responsible for both the increased amplitude of MLT rhythm and the phase advance. The increase in the amplitude of the body temperature could involve both MLT agonist and/or 5-HT2c antagonist properties of Ago.