Simultaneous measurement of behavior and the somatosensory-evoked potential in a rat model

Studies have shown that specific characteristics of somatosensory evoked potentials (SEPs) reflect nociception in both animals and humans. A relationship between SEPs and the unpleasantness of noxious stimulation in rats has recently been demonstrated using Pavlovian fear conditioning, consisting of a training phase in which a conditioned stimulus (CS) is paired with an unconditioned stimulus (US) to elicit the SEPs. After the training, CS-induced fear-conditioned behavior serves as a readout parameter for aversion to the US (i.e., the SEP stimulation paradigm). To prevent the animals from gnawing the stimulation cables that are necessary for generating SEPs, investigators have used a tight-fitting jacket that restrains the rats but also inhibits behavioral measurement. The use of a neck collar is an alternative technique that not only prevents cable gnawing but also allows the animals unrestricted movement while enabling investigators to assess fear-conditioned behavior and measure SEPs. The current study explores the effects of the tight-fitting jacket and the neck collar on SEPs. A within-subjects design was used for recording the SEP of each rat while the animal wore the collar or jacket. Both conditions show a similar SEP morphology, but data from the collar-wearing rats indicated an increase of the N150 peak amplitude (associated with emotional arousal) and peak latencies that appeared to be shorter. Thus the collar will be useful in future studies as it allows the simultaneous evaluation of SEPs and behavior