Effects of a selective serotonin reuptake inhibitor escitalopram on the cutaneous silent period: a randomized controlled study in healthy volunteers.

The cutaneous silent period (CSP) involves a transient inhibition of the electromyographic (EMG) activity in the hand muscles induced by a painful electrical stimulation of the digital nerves. The neurotransmitters potentially involved in mediating the CSP have not been completely elucidated thus far. However, few studies suggest that the monoaminergic system may play a role in the CSP. We elicited CSPs in the first dorsal interosseous muscle of the right hand before and 3h after administration of a single oral dose of the selective serotonin reuptake inhibitor escitalopram (20mg) or placebo. The two experimental sessions (drug and placebo) were performed in a random order at ≥1-week intervals. All recordings were numbered anonymously and analysed offline in a blind manner by one investigator. A significant increase in the CSP duration was observed 3h after escitalopram administration (p=0.01), and no changes were observed in the reflex latency and subjective pain sensation (p>0.05). No significant changes were observed in the CSP duration in subjects who received the placebo (all, p>0.05). Our results indicate that escitalopram increases the central disposition of serotonin and increases the activity of the spinal inhibitory interneurons on the α-motoneurons of the hand muscles. Thus, our results indicate the involvement of the monoaminergic system in controlling the spinal pain mechanisms by supraspinal descending pathways originating from the brainstem neural structures.

Cutaneous silent period in hand muscles is lengthened by tramadol: Evidence for monoaminergic modulation?

The purpose of this study was to shed light on the neurochemical modulatory mechanisms of the noxious spinal inhibitory cutaneous silent period (CSP). We study the effects of 100mg of oral tramadol in 11 healthy volunteers. Tramadol has low affinity for opioid receptors and has the ability to inhibit serotonin and noradrenaline reuptake. We elicited CSPs in the first dorsal interosseus muscle and noxious withdrawal flexor reflexes (NWR) in the right biceps femoris muscle before, 30 min and each hour up to the 6th after tramadol. Subjective pain sensation was checked on an 11-point numerical scale. Tramadol increased duration of CSP, and reduced the NWR area under the curve maximally 2h after tramadol and paralleled the reduction of subjective pain perception. We suggest that the monoaminergic action of tramadol reinforces the activity of spinal inhibitory interneurons on α-motoneurons for the hand muscles.