Administration of cholecystokinin sulphated octapeptide (CCK-8S) induces changes on rat amino acid tissue levels and on a behavioral test for anxiety.

1. The effect of the intraperitoneal administration of cholecystokinin sulphated octapeptide (CCK-8S) (10 nmol/kg i.p.) on endogenous levels of several amino acids in five areas of the rat brain was analyzed. The olfactory bulb, hypothalamus, hippocampus, cerebral frontal cortex, and corpus striatum were evaluated. In addition, the effects of CCK-8S and PD 135,158 (1 mg/kg), a selective CCK(B) antagonist, on the performance of rats submitted to a dark/light transition test were also studied. 2. Upon administration of CCK-8S, the concentration of glutamate was reduced (27%) in the olfactory bulb. The same was observed when the levels of glycine (31%) or alanine (43%) were determined. No significant effects were produced by CCK-8S on cortical and hypothalamic levels. In the hippocampus, the concentration of both glutamate (27%) and taurine (29%) were reduced, whereas the levels of GABA in the striatum (29%) were increased. 3. After a single injection of CCK-8S, the time spent by the rats in the illuminated site of the dark/light transition test box, was not changed. On the contrary, the administration of PD 135,158 increased the time spent in the lighted compartment. 4. These results show that systemic administration of CCK-8S produced regional specific changes in brain amino acids, without producing any significant behavioral modification in the rat exposed to a dark/light box. In contrast, the selective CCKB receptor antagonist, PD 135,158, induces anxiolytic-like action in an animal model of anxiety.