Anticonvulsant properties of CGP 37849 and CGP 39551, two novel phosphono-amino acids which are competitive NMDA receptor antagonists, were examined in rodents. At optimal pretreatment times CGP 37849 suppressed electroshock-induced seizures in mice and rats with ED50s ranging from 8 to 22 mg/kg after oral administration, and 0.4 to 2.4 mg/kg after i.v. and i.p. injection. Relative to CGP 37849, CGP 39551 was more potent after p.o. (ED50 3.7-8.1 mg/kg), and less potent after i.v. or i.p. treatment (ED50 2.7-8.7 mg/kg). Following oral treatment, the duration of action of CGP 37849 was about 8 h, while CGP 39551 still showed good activity after 24 h (ED50 8.7 mg/kg, mouse; 21 mg/kg, rat). Both compounds were anticonvulsant at doses below those at which overt behavioural side effects were apparent. CGP 39551 delayed the development of kindling in rats at doses of 10 mg/kg p.o. and above, and showed weak anticonvulsant activity against pentylenetetrazol-evoked seizures. CGP 37849 and CGP 39551 are the first competitive NMDA antagonists to show oral anti-convulsant properties in a therapeutically-useful dose-range, and hence are interesting candidates for novel antiepileptic therapy in man.
There is a need to identify subtype-specific ligands for mGlu receptors to elucidate the potential of these receptors for the treatment of nervous system disorders. To date, most mGlu receptor antagonists are amino acid-like compounds acting as competitive antagonists at the glutamate binding site located in the large extracellular N-terminal domain. We have characterized novel subtype-selective mGlu(5) receptor antagonists which are structurally unrelated to competitive mGlu receptor ligands. Using a series of chimeric receptors and point mutations we demonstrate that these antagonists act as inverse agonists with a novel allosteric binding site in the seven-transmembrane domain. Recent studies in animal models implicate mGlu(5) receptors as a potentially important therapeutic target particularly for the treatment of pain and anxiety.
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