Peripheral pathway of the blood pressure raised by exciting habenular nuclei

The electrical stimulation of the habenula (4 V, 100 Hz, 9 s) raised the arterial blood pressure (P less than 0.01) and quickened the heart rate of rats (P less than 0.05). Also, splanchnic nerve discharges were increased (P less than 0.01), the pupils dilated and the ear arteries constricted. The pressor effect was obviously weakened by phentolamine iv (P less than 0.01) and strengthened by bilateral vagotomy (P less than 0.05). The pressor effect disappeared after spinal cord transected at C1. Morphine iv elevated pain threshold (P less than 0.01) and eliminated the pain threshold change caused by exciting habenula. The pressor response of habenula was not influenced by elevating the pain threshold. The results suggest that the pressor effect of habenula occurs via the sympathetic vasoconstrictor fibers, vagus nerve exerts inhibition on the effect and the pressor effect of habenula is not a pain response caused by exciting habenula itself.