Behavioral evidence for a crossed ascending pathway for pain transmission in the anterolateral quadrant of the rat spinal cord

Thresholds of two behavioral responses to noxious pressure of the hindpaws (withdrawal, vocalization) were analyzed before and 3 weeks after a lesion of various quadrants of the spinal cord at the cervical level. The threshold of the spinal reflex could not be modified. Threshold of vocalization elicited by the pressure of one hindpaw was significantly increased when, and only when, the opposite ventrolateral quadrant was cut. These results emphasize the role of the lateral spinothalamic tract in the transmission of noxious messages.