Electrical stimulation of the midbrain mediates metastatic tumor growth.

Pulmonary metastases were counted 10 days after female rats received tail-vein injections of Walker-256 carcinosarcoma cells. Previous observations that halothane anesthesia plus hind-limb amputation increases the number of metastases were confirmed. Amputation under the analgesia of electrical stimulation of the midbrain was found to increase metastatic activity. However, the stimulus-produced analgesia alone also increased the number of metastases. Systemically administered naloxone blocked the analgesic effect of midbrain stimulation but did not block the increase in the number of pulmonary metastases.