title: Differential processing of laser stimuli by Aδ and C fibres in major depression.
abstract: Clinical studies have revealed that up to 92% of major depressed patients report pain complaints such as back or abdominal pain. Furthermore, patients suffering from depression exhibit increased superficial pain thresholds and decreased ischemic (deep) pain thresholds during experimental pain testing in comparison to healthy controls. Here, we aimed to investigate a putative role of Aδ- and C-fibre activation in altered pain perception in the disease. Laser-evoked potentials (LEPs) of 27 unmedicated depressed patients and 27 matched controls were recorded. Aδ and C fibres were activated separately. Amplitudes and latencies of N2 and P2 peaks of Aδ- (Aδ-LEP) and C-fibre- (C-LEP) related LEPs were evaluated. Depressed patients showed significantly decreased Aδ-LEP amplitudes (N2 peak: P=0.019; P2 peak: P=0.024) and delayed C-LEP latencies (P2 peak: P=0.0495; N2 peak: P=0.0556). In contrast, C-LEP amplitudes and Aδ-LEP latencies were unaffected. Our results might be suggestive of the differential impact of physiological changes on pain processing in depression. Thus, Aδ-LEP might reflect the physiological correlate of the augmented superficial pain thresholds during depression. On the contrary, the C-fibre component mediates the facets of pain processing, outlasting the stimulation period, and has been shown to be exaggerated in chronic pain states. Therefore, the functional over-representation of the C-fibre component found in our study might be a possible link between depression and associated pain complaints.
authors.affiliation: Pain & Autonomics - Integrative Research (PAIR), Department of Psychiatry and Psychotherapy, Philosophenweg 3, University Hospital, Jena, Germany Biomagnetic Center, Department of Neurology, University Hospital, Jena, Germany Institute of Psychology, University of Oldenburg, Oldenburg, Germany Department of Biological and Clinical Psychology, Institute of Psychology, Friedrich-Schiller-University, Jena, Germany.
authors.forename: Janneke
authors.initials: J
authors.lastname: Terhaar
authors.forename: Filipa Campos
authors.initials: FC
authors.lastname: Viola
authors.forename: Marcel
authors.initials: M
authors.lastname: Franz
authors.forename: Sandy
authors.initials: S
authors.lastname: Berger
authors.forename: Karl-Jürgen
authors.initials: KJ
authors.lastname: Bär
authors.forename: Thomas
authors.initials: T
authors.lastname: Weiss
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001703:Biophysics; D003865:Major Depressive Disorder / Q000473:pathology*; D004569:Electroencephalography / Q000379:methods; D005073:Evoked Potentials, Somatosensory / Q000502:physiology / Q000528:radiation effects; D005260:Female; D006801:Humans; D007834:Lasers / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000187:drug effects* / Q000502:physiology; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology / Q000528:radiation effects*; D010147:Pain Measurement; D058748:Pain Perception / Q000528:radiation effects; D017288:Pain Threshold / Q000502:physiology* / Q000528:radiation effects; D010775:Photic Stimulation; D011930:Reaction Time