JOURNAL OF NEUROTRAUMA 25:1323–1334 (November 2008) © Mary Ann Liebert, Inc. DOI: 10.1089/neu.2008.0575 Characteristics of Mid- to Long-Latency Spinal Somatosensory Evoked Potentials following Spinal Trauma in the Rat Benjamin M. Ellingson, 1 Shekar N. Kurpad, 2 and Brian D. Schmit 1 Abstract The purpose of this study was to develop and implement a new technique for repeated monitoring of spinal mid- to long-latency somatosensory evoked potentials (SpSEPs) during sciatic nerve stimulation following re- covery from spinal cord injury (SCI) in rats. Results of this study showed significant reproducibility of SpSEP components between specimens (analysis of variance [ANOVA], p  0.05) and recording days (ANOVA, p  0.700) using this technique. SpSEP amplitudes were significantly reduced (50% of uninjured amplitude, ANOVA, p  0.001) following SCI and remained depressed for 10 weeks post-injury. SpSEP amplitude fol- lowing high-intensity stimuli ( 1mA) correlated with BBB locomotor score (Pearson, R  0.353, P  0.001). Characteristics of the mid- to long-latency SpSEPs suggest these components may reflect the integrity of the lateral pain pathway within the spinothalamic tract (STT). The technique and data presented in this study may be useful in future studies aimed at quantifying spinal cord integrity following injury and treatment using the rat model of SCI. Key words: sensory function; spinal somatosensory evoked potentials; traumatic spinal cord injury 1323 Introduction D ESPITE EVIDENCE SUPPORTING the use of somatosensory evoked potentials (SEPs) for assessing spinal cord in- tegrity during surgery (Daube, 1999), following traumatic in- jury (Ziganow, 1986; Bloom and Goldberg, 1989) and during pathologies such as spondylotic myelopathy (Perlik and Fisher, 1987; de Noordhout et al., 1998), SEPs are not regu- larly employed in experimental models of spinal cord injury (SCI). Since many new treatment paradigms are being de- veloped with the use of animal models, there is a need for a reliable quantitative method of repeatedly assessing spinal cord integrity in vivo. Thus, the primary objective of this study was to introduce a new, noninvasive technique for se- rial monitoring spinal somatosensory evoked potentials (SpSEPs) in the rat. Following development of this technique, we aimed to characterize the large amplitude mid- to long- latency components of the SpSEPs for up to 70 days after a contusion injury. Cortical SEPs have been used previously to quantify spinal cord integrity after SCI in some animal models, although the methodologies employed are often invasive (Simpson et al., 1981; Fehlings et al., 1988; Raines et al., 1988; Fehlings et al., 1989; Lee et al., 2005), the measurements are sensitive to anes- thetic agents (Mongan and Peterson, 1993; Rojas et al., 2006), and changes in core body temperature cause recordings to drift (Oro and Haghighi, 1992). Fehlings et al. (1988) char- acterized cortical SEPs in the rat by stimulating the exposed sciatic nerve and recording extradural brain potentials. Sim- ilarly, Lee et al. (2005) recorded cortical SEPs in the rat by placing a stimulation electrode into the sciatic nerve and recording the resulting potentials within the rat sensorimo- tor cortex. The invasive nature of these methodologies does not allow serial recordings of cortical SEPs to be taken from the same animal during recovery from SCI. Recently, inves- tigators have developed less invasive techniques via needle electrodes placed subcutaneously over the scalp to obtain cortical SEP recordings (Oguzhanoglu and Kurt, 2001; Gar- cía-Alías et al., 2003). Despite the reduced invasiveness of the cortical recordings, the technique has not achieved wide- spread use, possibly due to the attenuation of cortical SEP amplitudes under anesthesia. Spinal evoked potentials (i.e., SpSEPs) offer an appealing alternative to cortical SEPs for assessing the integrity of so- 1 Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin. 2 Department of Neurosurgery, Medical College of Wisconsin, Milwaukee, Wisconsin.