EFFECTS OF SINGLE AND LONG-TERM ADMINISTRATION OF NIFEDIPINE ON NOCICEPTION AND STEREOTYPED BEHAVIOR OF RATS

In the present investigation, nociception and stereotyped behavior wer e evaluated in 3-month old male Wistar rats after a single nifedipine dose (2.5 and 5.0 mg/kg, ip, 1 h before testing, 6-7 rats per group fo r stereotypy studies and 15 animals per group for nociception experime nts) or after long-term nifedipine treatment (2.5 mg/kg, ip, twice dai ly for 30 days,with testing performed 72 or 96 h after the last inject ion, 7 rats per group for stereotypy studies and 14-16 animals per gro up for nociception experiments). Stereotypy was induced with 2.5 mg/kg amphetamine, ip, and nociception was measured by the tail-immersion t est. Administration of a single nifedipine dose did not modify nocicep tion or amphetamine-induced stereotypy (with a mean +/- SEM tail-withd rawal latency of 4.5 +/- 0.5 s for control, 4.4 +/- 0.3 s for 2.5 mg/k g nifedipine and 4.7 +/- 0.7 s for 5.0 mg/kg nifedipine and with mean +/- SEM sum of stereotypy scores of 32.5 +/- 1.6 for control, 29.1 +/- 1.0 for 2.5 mg/kg nifedipine and 29.1 +/- 1.6 for 5.0 mg/kg nifedipin e). Withdrawal from long-term nifedipine treatment did not affect ster eotyped behavior (with mean +/- SEM sum of stereotypy scores of 28.7 /- 1.6 for control and 30.7 +/- 1.3 for nifedipine-treated rats) but s ignificantly increased tail-withdrawal latencies (with a mean +/- SEM tail-withdrawal latency of 4.1 +/- 0.3 s for control and 6.4 +/- 0.6 s for nifedipine-treated rats). Therefore, long-term nifedipine treatme nt induced plastic modifications in nociception but not in stereotyped behavior. The possible mechanisms underlying these results are discus sed in the light of the effects of long-term calcium antagonist admini stration on the regulation of dopaminergic receptors and calcium chann els.