Spinal pathways of nociceptive information evoked by short CO2 laser pulse in rats

This study aimed to determine the relative importance of several spinal ascending pathways in conveying laser pulse activated A-delta and C-fiber information by using both awake and anaesthetized rats. Rats were subjected to spinal cord lesion (between T10-T12) under general anesthesia. Three types of lesion were made; dorsal column (DC, n = 4), bilateral dorsal lateral funiculus lesion (DLF, n = 4), and bilateral ventral quandrant lesion (VQ, n = 3). In normal awake rats, a laser pulse (10 watts intensity and 10 ms duration) applied to the plantar surface of the hind foot could evoke two prominent cortical potentials, one early and one late component in the contralateral somatosensory cortex. The early negative potential had a latency of 52.8 +/- 6.8 ms (mean +/- S.E.M.) and amplitude of 0.066 +/- 0.011 mV, while the late component had a latency of 264.6 (4.6 ms and an amplitude of 0.143 +/- 0.014 mV. After DC lesion, only latency of the early response was significantly lengthened (p < 0.05). Latency and amplitude of the early response were reduced markedly (p < 0.01) after bilateral DLF lesion. The change in the late response was significant only in the latency (p < 0.01). The peak amplitude of both early and late responses decreased significantly (p < 0.01) after VQ lesion. In rats with acute preparation, both of the DC and DLF lesions had no significant effect on the laser-evoked late response. The lesion of the VQ completely eliminated the late response.