Warner, R., Hudson-Howard, L., Johnston, C. and Skolnick, M. Serotonin involvement in analgesia induced by transcranial electrostimulation. Life Sciences. 46:1131-8, 1990.

The experiments described here were intended to investigate whether serotonin (5HT) may be involved in analgesia induced by low current CES. The CES stimulus is a 10 µA, 10 Hz, pulsed current transmitted via electrodes in the pinnae. Combinations of the following were given as intraperitoneal injections: 300 mg/kg p-chlorophenylalanine (pCPA) 48 hours before testing, 100 mg/kg 5-hydroxytryptophan (5HTP) 30 minutes before testing and the saline vehicle for these drugs. Rats were tested prior to and 30 minutes after CES or sham CES. Testing for analgesia consisted of putting progressively increasing pressure on the rat tail 1/4 inch from the tip with a pneumatically driven, right angle wedge. The amount of pressure at which the rat moved its tail was measured both before and after CES, or sham CES, and recorded as the difference in tolerated peak pressure (DTPP). CES produced analgesia as manifested by a 613% increase in DTPP compared with sham CES treatment values. Among CES treated rats, pretreatment with pCPA decreased DTPP 91.5% compared with saline control values, indicating 5HT involvement. 5HTP restored CES induced analgesia in pCPA treated rats to the level of saline treated control animals, confirming 5HT involvement.