Association between wind-up ratio and central serotonergic function in healthy subjects and depressed patients
Department of Psychiatry, Ruhr University Bochum, LWL University Hospital Bochum, Alexandrinenstrasse 1, 44791 Bochum, Germany. Neuroscience Letters
(Impact Factor: 2.03).
09/2011; 504(2):176-80. DOI: 10.1016/j.neulet.2011.09.033
Temporal summation of C-fiber evoked responses generates an increase in action potential discharge in second-order neurons and in perceived pain intensity (wind-up). This may be related to the central serotonergic system which modulates and partly inhibits sensory input. Aim of the study was to investigate the relationship between wind-up and serotonergic activity using loudness dependence of auditory evoked potentials (LDAEP). 18 healthy subjects were compared to 18 patients with major depression, a disease with a putative serotonin deficit. They were examined with quantitative sensory testing (QST) using the protocol of the German Research Network on Neuropathic Pain (DFNS), including the wind-up ratio (WUR), LDAEP, and psychometric measurements. We found a slight positive correlation between WUR and LDAEP both in healthy controls and depressed patients combined (r=0.340, p=0.043), indicating that WUR may be modulated by serotonergic activity. It can be concluded that inhibitory control to noxious stimuli is partly associated with the central serotonergic function as indicated by LDAEP.
Available from: Jason G Craggs
- "In other words, if the input stimulus yields an elevated pain rating (e.g., 100), then subsequent ratings can only stay the same or decrease and temporal summation cannot occur. Regarding stimulus modality, TSSP has been demonstrated using heat (Edwards and Fillingim, 2001; Granot et al., 2003), electrical (Pedersen et al., 1998), cold (Price et al., 2002), pinprick (Rolke et al., 2006; Uhl et al., 2011) and mechanical pressure stimuli (Staud et al., 2003; Nie et al., 2005). However, no study to date has directly compared TSSP response magnitude between two modalities, so it is unknown whether one type of stimulus confers an advantage over another in eliciting temporal summation, or whether there is intraindividual specificity of TSSP to stimuli. "
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Temporal summation of second pain (TSSP) is relevant for the study of central sensitization, and refers to increased pain evoked by repetitive stimuli at a constant intensity. While the literature reports on participants whose pain ratings increase with successive stimuli, response to a TSSP protocol can be variable. The aim of this study was to characterize the full range of responses to a TSSP protocol in pain-free adults.
Three hundred twelve adults received a train of brief, repetitive heat stimuli at a fixed temperature and rated the intensity of second pain after each pulse. TSSP response (Δ in pain ratings) was quantified using the most common methods in the literature, and response groups were formed: TSSP (Δ > 0), no change (Δ = 0), and temporal decrease in second pain (TDSP) (Δ < 0). A cluster analysis was performed on the Δ values to empirically derive response groups.
Depending on how TSSP response was quantified, 61-72% of the sample demonstrated TSSP, 11-28% had no change in pain ratings and 0-20% demonstrated TDSP. The cluster analysis found that the majority (59%) of participants fell in the no change cluster, 29% clustered into the TSSP group and 12% in the TDSP cluster.
Using a fixed thermal paradigm, pain-free adults exhibit substantial variability in response to a TSSP protocol not well characterized by group-mean slopes. Studies are needed to determine TSSP response patterns in clinical samples, identify predictors of response and determine the clinical implications of response variability.
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ABSTRACT: The objective of this study was to examine the subgroup of patients with chronic pruritus with dysesthetic subqualities for the presence of psychiatric comorbidities and to evaluate whether anxiety and depression make a difference in perception of somatosensory stimuli in quantitative sensory testing (QST). Forty-nine patients underwent routine diagnostics, a standardised QST testing battery, a psychosomatic evaluation for psychic comorbidities and filled out 2 questionnaires: the Patient Health Questionnaire for the assessment of depressive mood and the State Trait Anxiety Inventory. Twenty-seven (55.1%) of the sample had at least one psychiatric comorbid diagnosis. QST parameters were not correlated to anxiety and depression levels. We conclude that psychosomatic evaluation should become part of routine diagnostics of these patients in order to detect and treat psychiatric comorbidity. However, research on somatosensory aspects in these patients seems not to be affected by the levels of anxiety and depression.
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