Verruculogen is a tremorgenic mycotoxin, first isolated from Penicillium verruculosum in 1972. The structure was resolved as an indole alkaloid in 1974. Verruculogen is produced by several species of Penicillium and Aspergillus and its presence is a useful taxonomic phenotypic marker. The tremorgenic action of verruculogen is associated with increases in spontaneous glutamate and aspartate release, decreases in GABA levels and, at toxic doses, an increase in the number and decrease in the affinity of DHP receptors in rat cortex. In in vitro guinea pig ileum preparations, verruculogen causes an increase in contractile responses due to electrical field stimulation, attributed to enhancement of acetylcholine from presynaptic nerve terminals. Verruculogen also inhibits Ca2+-activated K+ channels, and is a cell cycle inhibitor blocking division at the M phase.