tokens: Gamma - hexachlorocyclohexane ( gamma - HCH ) , the active ingredient of the insecticide lindane , has been shown to decrease seizure threshold to pentylenetrazol ( PTZ ) 3 h after exposure to gamma - HCH and conversely increase threshold to PTZ - induced seizures 24 h after exposure to gamma - HCH ( Vohland et al . 1981 ) .