Labelling of cells in the medulla oblongata and the spinal cord of the monkey after injections of horseradish peroxidase in the thalamus.

Injections of horseradish peroxidase were performed in macaque monkeys in the intralaminar and the ventroposterior thalamic region, respectively. Following injection in the intralaminar region labelled cells were present in the marginal zone both in the spinal trigeminal nuclues and in the spinal dorsal horn. The same areas contained labelled cells after injections in the ventroposterior thalamic region, but in such experiments labelled cells were also present in the lamina IV-V region of the spinal cord, in the gracile and main cuneate nuclei and in the external cuneate nucleus. Thus, the marginal zone of the spinal cord appears to project to at least two of the thalamic regions receiving spinothalamic fibres in the monkey.