The effects of rubidium, caesium and quinine on 5-HT-mediated behaviour in rat and mouse--2. Caesium.

Rats and mice were given either CsCl (3 mmol/kg, s.c.) or saline (as control), twice daily for 3 days. The administration of tranylcypromine (TCP) (15 mg/kg, i.p.) to rats pretreated with CsCl produced the 5-HT behavioural syndrome. Pretreatment with CsCl also enhanced the syndrome induced by p-chloroamphetamine (3 mg/kg, i.p.) or by TCP (15 mg/kg, i.p.) plus L-tryptophan (50 mg/kg, i.p.). p-Chlorophenylalanine (300 mg/kg, i.p., daily on 2 consecutive days) or (-)-propranolol (20 mg/kg, i.p.), pindolol (4 mg/kg, i.p.) and ritanserin (0.4 mg/kg, s.c.), all prevented the behavioural syndrome induced by CsCl and TCP in rats. Pretreatment of rats with CsCl potentiated the 5-HT syndrome, elicited by the 5-HT agonists, 8-OH-DPAT (0.5 mg/kg, s.c.), 5-MeODMT (2 mg/kg, s.c.) and quipazine (25 mg/kg, i.p.). Pretreatment with CsCl potentiated the 5-HT2-mediated head-twitches in the mouse but had no effects on hypothermia in the mouse induced by 8-OH-DPAT (0.5 mg/kg, s.c.). The rate of synthesis of 5-HT in the whole brain (excluding cerebellum) was enhanced by pretreatment with CsCl. The enhancement of 5-HT neuronal function by caesium may be related to its ability to block K(+)-channels in neuronal membranes.