title: Vertex-recorded, rather than primary somatosensory cortex-recorded, somatosensory-evoked potentials signal unpleasantness of noxious stimuli in the rat.
abstract: In the present study, we investigated in the rat whether vertex- or primary somatosensory cortex-recorded somatosensory-evoked potentials (Vx-SEP/SI-SEP, respectively) signal unpleasantness of noxious stimuli. Therefore, initially we characterised fentanyl effects (0, 20, 40 or 50 microg/kg/h) on somatosensory and auditory processing by recording Vx-/SI-SEPs and vertex- and primary auditory cortex-recorded auditory-evoked potentials (Vx-/AI-AEPs, respectively). Subsequently, in a separate experiment, the animals were subjected to a Pavlovian fear-conditioning paradigm. The noxious stimuli applied to evoke Vx-/SI-SEPs (unconditioned stimulus (US)) were paired to a tone (conditioned stimulus (CS)) under 'steady state' conditions of 0, 20, 40 or 50 microg/kg/h fentanyl. Vx-/SI-SEPs were recorded simultaneously during these trials. After CS-US presentation, CS-induced fear-conditioned behaviour was analysed in relation to the SEPs recorded during CS-US presentation and the AEPs recorded in the first experiment. While the SI-SEP and AI-AEP were minimally but significantly affected, fentanyl dose-dependently decreased the Vx-SEP and Vx-AEP. The decrease of the Vx-SEP and Vx-AEP was parallelled by the dose-dependent decrease of the amount of CS-induced fear-conditioned behaviour. These results suggest that the dose-dependent decrease of the Vx-SEP amplitude, rather than of the SI-SEP, indicates that the US was experienced as less unpleasant. Next to an altered US processing, altered CS processing contributed to the decrease of the amount of CS-induced fear-conditioned behaviour as indicated by the dose-dependent decrease of the Vx-AEP.
authors.affiliation: Department of Clinical Sciences of Companion Animals, Section Anaesthesiology and Neurophysiology, Faculty of Veterinary Medicine, Utrecht University, P.O. Box 80.154, NL-3508 TD Utrecht, The Netherlands. P.Stienen@vet.uu.nl
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Stienen
authors.forename: Hugo
authors.initials: H
authors.lastname: van Oostrom
authors.forename: Ruud
authors.initials: R
authors.lastname: van den Bos
authors.forename: Harry N M
authors.initials: HN
authors.lastname: de Groot
authors.forename: Ludo J
authors.initials: LJ
authors.lastname: Hellebrekers
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D003214:Conditioning, Classical / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004569:Electroencephalography / Q000187:drug effects / Q000379:methods; D005072:Evoked Potentials, Auditory / Q000187:drug effects / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects / Q000502:physiology*; D005239:Fear / Q000502:physiology; D005283:Fentanyl / Q000494:pharmacology; D008297:Male; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000701:Analgesics, Opioid; D005283:Fentanyl