No abstract

Sulphated cholecystokinin octapeptide (CCK‐8s) is involved in feeding regulation as an anorexigenic neuropeptide in vertebrates. In rodents, i.c.v. administration of CCK‐8s has been shown to affect not only feeding behaviour, but also psychomotor activity. However, there is still no information available concerning the psychophysiological effects of CCK‐8s in goldfish. Therefore, in the present study, we examined the effect of synthetic goldfish (gf) CCK‐8s on psychomotor activity in this species. Intracerebroventricular administration of gfCCK‐8s at 0.1, 0.5 and 2.5 pmol g‐1 body weight (BW) did not affect swimming distance (locomotor activity). Because goldfish prefer the lower to the upper area of a tank, we used this as a preference test (upper/lower test) to assess anxiety‐like behaviour. Intracerebroventricular administration of gfCCK‐8s at 2.5 pmol g‐1 BW shortened the time spent in the upper area. The action of gfCCK‐8s mimicked that of FG‐7142 (the central‐type benzodiazepine receptor inverse agonist, an anxiogenic agent) at 5 and 10 pmol g‐1 BW. The anxiogenic‐like effect of gfCCK‐8s was abolished by treatment with the CCK receptor antagonist proglumide at 50 pmol g‐1 BW. We also investigated the localisation of CCK/gastrin‐like immunoreactivity in the goldfish brain. CCK/gastrin‐like immunoreactivity was observed in the anxiety‐related regions (the nucleus habenularis and the interpeduncular nucleus). These data indicate that gfCCK‐8s potently affects psychomotor activity in goldfish, and exerts an anxiogenic‐like effect via the CCK receptor‐signalling pathway.