Effects of noxious stimuli and anesthetic agents on substance P content in rat central nervous system.

Effects of noxious electrical tooth stimulations and intraarterial administration of bradykinin or inhalation of volatile anesthetics on substance P content in the diencephalon-mesencephalon, pons-medulla and the spinal cord were examined in the rat. Noxious stimulation by electrical long duration stimulation (type 2) of tooth pulp caused an increase of substance P content in the ponsmedulla. Inhalation of volatile anesthetics such as methoxyflurane and diethylether produced an increase of substance P content in the spinal cord; and in addition, methoxyflurane produced a decrease of substance P content in ponsmedulla. However, halothane did not produce any changes in substance P content in any parts of the central nervous system (CNS). These results suggest that volatile anesthetics such as diethyl-ether and methoxyflurane act on the substance P neuron and may modulate pain transmission through the action of substance P in the pons-medulla or the spinal cord.