Serial recording of sensory, corticomotor, and brainstem-derived motor evoked potentials in the rat

A method is presented for serial recording of corticomotor evoked potential s (CMEPs), brainstem-derived motor evoked potentials (BMEPs), and somatosen sory evoked potentials (SEPs) via permanently implanted cranial screws. One screw was positioned posterior to lambda (posterior screw), and two screws were positioned over the cortical hind limb areas (cortical screws). SEPs were elicited by stimulation of the hind paw and recorded from the contrala teral cortex. BMEPs were stimulated via the posterior screw and recorded fr om both hind limbs, whereas CMEPs were elicited by repeated bipolar stimula tion of the cortex and recorded from the contralateral hind limb. BMEPs and CMEPs differed in several points and can be considered as completely separ ate motor evoked potentials. While BMEPs consisted of a prominent negative peak with short latency (5-7.5 ms), CMEPs were represented by polyphasic si gnals with long latencies (17-22 ms). The cortical origin of the CMEPs was confirmed by transecting the corticospinal tracts, which abolished the CMEP s but spared the BMEPs. SEPs consisted of three consecutive peaks with mean latencies of the initial peak ranging between 15 and 17 ms. Dorsal column transection also abolished SEPs. In healthy rats, all three signals were re corded for six consecutive weeks. Signal parameters did not change signific antly within this observation period. Rats tolerated the screws and the rep eated measurements very well and no negative affect on animal behavior was noted. Thus, this method allows serial recording of SEPs, CMEPs, and BMEPs in chronic rat models.