Characteristics of reserpine-induced suppression of NaCl solution intake in rats

Effects of single and repeated administration of reserpine on time-limited drinking of a hypertonic (1.5% w/w) NaCl solution were investigated in rats to assess whether this drug possesses anxiolytic action. Rats adapted to a 23-hr water-deprivation schedule with a free-feeding regimen were allowed a daily 1-hr water rehydration session. In the single-administration experiment, reserpine (0.1, 0.2 and 0.4 mg/kg, IP) was administered to rats at 15 min or 23 hr before a drinking session, where the fluid available was 1.5% NaCl solution. Drug was administered every 7th day. In the repeated-administration experiment, reserpine (0.1 mg/kg/day) was injected daily for 10 days 15 min before each drinking session. The fluid available was water on the first 9 days and NaCl solution on the 10th day. Reserpine suppressed NaCl solution intake when it was singly administered at 15 min before the rehydration, whereas no significant change in the fluid intake occurred when it was administered 23 hr before drinking, even though rats showed ptosis in response to 0.2 and 0.4 mg/kg doses. Tolerance developed to the suppressing effect of repeated administration of reserpine on fluid intake, although ptosis and sedation continued and body weights decreased. Tolerance was almost complete after 11 days. The results suggest that reserpine does not have an anxiolytic effect.