Primate spinothalamic pathways: III. Thalamic terminations of the dorsolateral and ventral spinothalamic pathways.

The termination sites of the dorsolateral (DSTT) and ventral (VSTT) spinothalamic pathways were determined by using anterograde transport of horseradish peroxidase from the lumbar spinal cord in primates. One animal had no spinal cord lesion, while of two other animals, one received a midthoracic dorsolateral funiculus lesion, and the other received a midthoracic ventral quadrant lesion contralateral to the injection. The thalamic label in the animal with no spinal cord lesion was much less than the label in the two animals with spinal lesions. Moreover, in the animals with spinal lesions, HRP-labeled cells were found within the thalamus. Therefore, the remaining six animals received ipsilateral hemisections and bilateral dorsal column lesions, irrespective of the contralateral lesions. The thalamic label in the animals without contralateral lesions were assumed to represent the total spinothalamic input to the diencephalon. In these animals, label was located mainly in suprageniculate and pulvinar oralis, caudal and oral divisions of ventral posterior lateral nucleus, the lateral half of ventral posterior inferior nucleus, and zona incerta, while in the medial thalamus label was primarily in two distinct bands in medial dorsal nucleus and in the posterior dorsal portion of central lateral nucleus. Scattered lighter labeling was found in other thalamic nuclei. The pattern of terminal labeling observed in the ventral posterior lateral region was arranged in patches, while elsewhere in the thalamus a more uniform labeling pattern was observed. The thalamic label in animals with contralateral ventral quadrant lesions represented the terminations of the DSTT, while the label in animals with contralateral dorsolateral funiculus lesions represented VSTT terminations. The labeling pattern was similar between these two groups. However, there were small differences between them. These results indicate that DSTT and VSTT terminations largely overlap and innervate the lateral and medial thalamamus.