Labelling of cervival and thoracic spinal neurones following injections of horseradish peroxidase in the leg muscles of rats

Following injection of horseradish peroxidase (HRP) solution in the gastrocnemius muscle or the extensor digitorum longus muscle in neonatal and developing albino rats, some neurones in the cervical enlargement, mid-thoracic region and sacral region were labelled in addition to the region of the spinal cord from where the sciatic nerves emerged. The labelling was most probably the result of diffusion of HRP solution from the site of injection to nearby structures.