Is the loudness dependence of auditory evoked potentials modulated by the selective serotonin reuptake inhibitor citalopram in healthy subjects?

The loudness dependence of auditory evoked potentials (LDAEP) has been discussed as a non-invasive in vivo marker of central serotonergic function. Evidence for this has been found in animal studies, but studies in humans provide less consistent results. In this study, the relationship between LDAEP and directly modulated central serotonergic activity in healthy subjects was investigated. In a single-blind cross-over design, the LDAEP of female participants (age: 24.0 +/- 2.3 years) was measured under two conditions: (1) infusion of 20 mg citalopram diluted in 250 ml 0.9% saline and (2) infusion of 250 ml 0.9% saline as placebo. LDAEP was measured at five different time points before, during and up to 60 min after drug/placebo administration and dipole source analysis was performed. The increase of the central serotonin activity in response to citalopram was not accompanied by a significant change of the LDAEP compared to the placebo condition. The result underlines that the acceptance of LDAEP as a marker of central serotonergic function still needs further discussion.