Pharmacology zyxwvutsrqpo & Toxicology zyxwvutsrqpo 1992, 70, zyxwvutsr 1 15-1 20. zyxwvutsr Domoic Acid Toxicity zyx in Rats and Mice after IntracerebroventricularAdministration: Comparison with Excitatory Amino Acid Agonists Christian Chiamulera, Silvano Costa, Enzo Valerio and Angelo Reggiani Glaxo Research Laboratories, via Fleming 2, 1-37135 Verona, Italy (Received April 24, 1991; Accepted August 9, 1991) Abstract: A behavioural study of the domoic acid (D0M)-induced convulsive behaviour after intracerebroventricular administration was carried out in rats and mice. DOM-induced behaviours were compared to those elicited by other excitatory amino acid (EAA) agonists N-methyl-D-aspartate (NMDA), a-amino-3-hydroxy-5-methyl-4-isoxazole propi- onic acid (AMPA) and kainic acid (KA), in such a way as to assess the possible similarities between DOM-induced effects and EAA subtype receptor activation in vivo. In rat, DOM (0.03-3 nmol/rat) caused a complex pattern of convulsive behaviour, quantified by means of a 15-point rating scale. DOM-induced behavioural profile was characterized at the lower doses by “preconvulsive” behaviours as wet dog shakes, hypermotility, mild facial clonus. At higher doses, DOM caused clonic convulsions followed by the “status epilepticus” syndrome (wet dog shakes, forelimb clonus, rearing, salivation). Rats treated with KA (0.3-10 nmol/rat) showed an almost identical behavioural profile. AMPA (1-10 nmoll rat)-induced convulsive behaviour was similar to DOM and KA only at the higher doses. NMDA (0.25-10 nmol/rat) caused clonic convulsions but not “status epilepticus”. In mice, similar results were obtained: all the tested drugs induced generalized seizures, but only animals treated with DOM, KA and AMPA showed a prolonged sequence of seizures with forelimb clonus. Our results confirm the findings reported in the literature and support the hypothesis that DOM and KA act at the same EAA receptor. Recently, several people were intoxicated in Canada after eating cultured mussels ( M y t h s edulis L.), Many of them exhibited dramatic toxic reactions like disorientation, loss of consciousness, motor signs of limbic seizures and an apparently irreversible neurologic sequelae (Per1 et al. 1990; Teitelbaum et al. 1990). Accurate analysis performed by the National Research Council of Canada revealed the presence of domoic acid (DOM) in the mussel extracts (Quillian & Wright 1989). DOM, originally isolated from the sea-weed Chondria armata, is structurally related to the endogenous excitatory amino acid (EAA) glutamate. Several studies indicate that glutamate acts on at least four different sub- type receptors named after their preferred ligands N-methyl- D-aspartic acid (NMDA), a-amino-3-hydroxy-5-methyl-4- isoxazole propionic acid (AMPA), kainic acid (KA) and L- amino-4-phosphonobutirric acid (L-AP4) (Watkins et al. 1990). The activation of the NMDA, AMPA and KA sub- type receptors by the corresponding agonists causes acute behavioural effects in animals, the most common being convulsant activity (Schwarcz & Ben-Ari 1986). The neuro- toxic properties of KA were extensively studied (McGeer & McGeer 1982) and, in particular, a KA-induced “status epilepticus” in rats has been described and is commonly considered an animal model of human temporal lobe epi- lepsy and of seizure-related brain damage (Ben-Ari 1985; Lothman & Collins 198 1). Structural similarities between DOM and KA, isolated from the same family of algae as DOM, have led to the hypothesis that DOM-induced neurotoxicity is mediated by KA subtype receptor activation (Biscoe et al. 1976). This is also supported by electrophys- iological and binding studies (DeBonnel et al. 1989; Slevin et al. 1983). Finally, more recent findings have demonstrated the similarity of DOM and KA to induce convulsive behav- iour in mice (Tasker et al. 1989) and neurotoxicity in adult (Stewart et al. 1990; Sutherland et al. 1990; Tryphonas et al. 1990) and aged rats (Wozniak et al. 1990). In the present study we have investigated the behavioural and convulsive syndrome induced by DOM intracerebro- ventricularly in rats and mice with the aim of testing whether its behavioural profile could be related to a specific EAA sub- type receptor activation. To this purpose we have compared the effect of DOM with other EAA agonists such as NMDA, KA and AMPA. This comparison was performed by qualita- tive and quantitative evaluation of behaviour after intracere- broventricular administration, in an experiment designed to give comparable brain bioavailabilities of each drug. Materials and Methods Animals. Male CD-COBS rats (Charles River, Italy) weighing 275440 g and male CDI mice (Charles River, Italy) weighing 18-29 g were used. Animals were allowed food and water ad libitum except during the short time they were removed from their cages for testing. In all experiments animals were randomly allocated. Testing was performed in a normally lighted room between 8 a.m. and 1 p.m. Chemicals. The following drugs were used: AMPA from Research Biochemicals Inc., Natick MA, U.S.A.; DOM and KA from Sigma Chemical Company, St. Louis, MO, U.S.A.; chloramphenicol succi- nate from Farmitalia Carlo Erba, Nerviano, Italy; NMDA from Aldrich, Milwaukee WI, U.S.A.; 2,2,2-tribromoethanoI from Ald- rich, Beerse, Belgium. Drugs were intracerebroventricularly ad- ministered in a total volume of 10 pl/animal, dissolved with sodium phosphate 0.01 M buffer pH = 7.4. Control vehicles were prepared at the same pH value of the corresponding drug solution.