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Somatosensory-evoked potentials (SEPs) are used in humans and animals to increase knowledge about nociception and pain. Since the SEP in humans increases when noxious stimuli are administered unpredictably, predictability potentially influences the SEP in animals as well. To assess the effect of predictability on the SEP in animals, classical fear conditioning was applied to compare SEPs between rats receiving SEP-evoking electrical stimuli either predictably or unpredictably. As in humans, the rat’s SEP increased when SEP-evoking stimuli were administered unpredictably. These data support the hypothesis that the predictability of noxious stimuli plays a distinctive role in the processing of these stimuli in animals. The influence of predictability should be considered when studying nociception and pain in animals. Additionally, this finding suggests that animals confronted with (un)predictable noxious stimuli can be used to investigate the mechanisms underlying the influence of predictability on central processing of noxious stimuli. [ABSTRACT FROM AUTHOR]

Abstract: At present, the specific neurophysiologic methodology of recording pain-related evoked potentials is considered a most promising approach to objectively quantify pain in man. This study was designed to characterise and evaluate the use of somatosensory evoked potentials to study nociception in a canine model. To this aim, somatosensory evoked potentials were evoked by intra-epidermal electrical stimulation and recorded from the scalp in 8 beagle dogs. Characteristics determined were: (1) the conduction velocities of the peripheral nerve fibres involved, (2) the stimulus intensity response characteristics and (3) the evaluation of possible disturbance of the signals by muscular activity from the hind paw withdrawal reflex (EMG artefact). The results showed (1) the conduction velocities to be in the A-delta fibre range (i.e. fibres involved in nociception), (2) an increase in amplitude and a decrease in latency of the evoked potential following increasing stimulus intensities and (3) the absence of EMG artefact in the signals. These data indicate that the evoked potentials recorded, are related to nociception and thus are suited to quantitatively characterise the perception of noxious stimuli making this model useful for pain- and analgesia-related research. [Copyright &y& Elsevier]

Objective To study, the analgesic and sedative effects of different constant rate infusions (CRI) of dexmedetomidine, in the rat, by measurement of specific electroencephalographic parameters. The recorded parameters were somatosensory-evoked potentials (SEPs) and auditory-evoked potentials (AEPs), which have been shown to be related to analgesia and sedation respectively. Animals Nine male Wistar rats (HsdCpb:Wu, Harlan Netherlands BV, body weight 300–350 g). Methods Somatosensory-evoked potentials were recorded from the primary somatosensory cortex and the vertex location (SI/Vx-SEPs). Auditory-evoked potentials were recorded from the primary auditory cortex and vertex location (AI/Vx-AEPs). Primary somatosensory cortex and vertex location recorded SEPs and AI/Vx-AEPs were recorded alternately, during CRI of dexmedetomidine (4.0, 10.0, 20.0 μg kg−1 hour−1) and a control (saline). Results The primary somatosensory cortex-evoked potentials were not affected by the dexmedetomidine CRI, but the other three parameters were significantly affected; although the AI-SEP to a lesser extent than the Vx-SEP and Vx-AEP. A maximum effect on the Vx-AEP was reached at lower doses than on the Vx-SEP. Conclusions Based on the present findings, it is suggested that CRI of dexmedetomidine provided profound sedation at low doses, whereas higher doses are needed to provide concurrent analgesia. Clinical relevance A constant rate infusion of dexmedetomidine can be a valuable adjunct in the provision of sedation and/or analgesia. However, analgesia cannot be produced without sedation, and sedation is not necessarily accompanied by comparative degrees of analgesia. [ABSTRACT FROM AUTHOR]