The long-term objective is to define the fundamental basis for the selective toxicity of insecticides acting at the gamma-aminobutyric acid (GABA) receptor of mammals and insects. This is the target of major neurotoxic insecticides acting as both blockers and activators of the GABA-gated chloride channel. More than 5,000,000,000 pounds of these channel blockers have been used for pest control in the past 50 years and they range in chlorine content from 52-73%. The major channel blockers used at present, representing 6% of the insecticide market, are endosulfan and lindane and this market share will increase with expanded use of the newly-commercialized polyhalogenated fipronil. The activators such as avermectin and moxidectin are also used in ever increasing quantities as insecticides and anthelmintics. More specifically, the goal is to provide toxicological profiles and maps for the insecticide blocker site and the insecticide activator site by designing and using high-affinity radioligands (the insecticide itself or a closely-related model compound) and photoaffinity probes to study binding site interactions and localization in the brain and chloride channel. Emphasis will be placed on the discovery of differences between the GABA receptors of mammals and insects that confer preferential sensitivity to insecticides and safety to mammals. The proposal is to prepare suitable radioligands and photoaffinity probes and use them to localize the binding sites as to brain region, receptor subunit and specific derivatized amino acid(s) in the chloride channel of mammals (bovine) and insects (Drosophila); the chemistry to achieve this end comes largely from discoveries in this laboratory. The research also involves rat cerebellar granule cells in primary culture to study radioligand binding and chloride flux in intact cells, localization of radioligand binding in mouse brain slices following in vitro and in vivo exposure to unlabeled toxicants, and receptors derived from Sf9 cells transfected with cDNs of human GABAa receptor subunits.

National Institute of Health (NIH)
National Institute of Environmental Health Sciences (NIEHS)
Research Project (R01)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG4-ALTX-3 (01))
Program Officer
Lawler, Cindy P
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of California Berkeley
Public Health & Prev Medicine
Schools of Earth Sciences/Natur
United States
Zip Code
Chen, Ligong; Xue, Ling; Giacomini, Kathleen M et al. (2011) GABAA receptor open-state conformation determines non-competitive antagonist binding. Toxicol Appl Pharmacol 250:221-8
Chen, Ligong; Durkin, Kathleen A; Casida, John E (2006) Spontaneous mobility of GABAA receptor M2 extracellular half relative to noncompetitive antagonist action. J Biol Chem 281:38871-8
Sammelson, Robert E; Caboni, Pierluigi; Durkin, Kathleen A et al. (2004) GABA receptor antagonists and insecticides: common structural features of 4-alkyl-1-phenylpyrazoles and 4-alkyl-1-phenyltrioxabicyclooctanes. Bioorg Med Chem 12:3345-55
Sammelson, Robert E; Casida, John E (2003) Synthesis of a tritium-labeled, fipronil-based, highly potent, photoaffinity probe for the GABA receptor. J Org Chem 68:8075-9
Caboni, Pierluigi; Sammelson, Robert E; Casida, John E (2003) Phenylpyrazole insecticide photochemistry, metabolism, and GABAergic action: ethiprole compared with fipronil. J Agric Food Chem 51:7055-61
Ratra, Gurpreet S; Erkkila, Brian E; Weiss, David S et al. (2002) Unique insecticide specificity of human homomeric rho 1 GABA(C) receptor. Toxicol Lett 129:47-53
Hold, K M; Sirisoma, N S; Sparks, S E et al. (2002) Metabolism and mode of action of cis- and trans-3-pinanones (the active ingredients of hyssop oil). Xenobiotica 32:251-65
Sirisoma, N S; Ratra, G S; Tomizawa, M et al. (2001) Fipronil-based photoaffinity probe for Drosophila and human beta 3 GABA receptors. Bioorg Med Chem Lett 11:2979-81
Sirisoma, N S; Hold, K M; Casida, J E (2001) alpha- and beta-Thujones (herbal medicines and food additives): synthesis and analysis of hydroxy and dehydro metabolites. J Agric Food Chem 49:1915-21
Hold, K M; Sirisoma, N S; Casida, J E (2001) Detoxification of alpha- and beta-Thujones (the active ingredients of absinthe): site specificity and species differences in cytochrome P450 oxidation in vitro and in vivo. Chem Res Toxicol 14:589-95

Showing the most recent 10 out of 14 publications