The octadecaneuropeptide exerts an anxiogenic-like action in goldfish

I.c.v. administration of the octadecaneuropeptide (ODN), a peptide derived from diazepam-binding inhibitor (DBI), induces anorexigenic and anxiogenic-like actions in rodents. We have recently shown that, in goldfish, i.c.v. injection of ODN also reduces food consumption via the metabotropic endozepine receptor. However, there is little information regarding the structure of DBI and the psychophysiological roles of endozepines in fish. Therefore, in the present study, we isolated and cloned a cDNA encoding goldfish DBI. The deduced sequence exhibits high similarity with non-mammalian DBIs, and we investigated the effect of homologous ODN on psychomotor activity in goldfish. i.c.v. injection of synthetic goldfish ODN at 10 pmol/g body weight (BW) stimulated locomotor activity. Since intact goldfish placed in a tank with both black and white background areas prefers the black compartment, we developed a method for measuring the time taken for fish to move from the black to the white area. I.c.v. administration of diazepam (35 and 350 pmol/g BW) decreased, whereas i.c.v. administration of ODN (10 pmol/g BW) or the central-type benzodiazepine receptor inverse agonist FG-7142 (9 pmol/g BW) increased the time taken to move from the black to the white background area. The anxiogenic-like effect of ODN was blocked by the central-type benzodiazepine receptor antagonist flumazenil (100 pmol/g BW), but was not affected by the metabotropic endozepine receptor antagonist cyclo1-8[d-Leu ⁵]octapeptide (100 pmol/g BW). These data indicate that ODN can potently affect locomotor and psychomotor activities in goldfish and that this action is mediated via the central-type benzodiazepine receptor-signaling pathway.