SEROTONERGIC AGONISTS AND ANTAGONISTS AFFECT ENDURANCE PERFORMANCE IN THE RAT

The purpose of this experiment was to examine the effects of administration of serotonergic (5-HT) agonist and antagonist drugs on run-time to exhaustion (RUN-EXH) in male and female rats. RUN-EXH was reduced (p<0.05) in a dose related manner by increasing dosages of quipazine dimaleate (QD: general 5-HT agonist) (0-5 mg.kg-1 i.p.) administered immediately prior to exercise (treadmill running at 20 m.min-1 and 5 % grade). Conversely, RUN-EXH was increased (p<0.05) by the greatest dosage of LY 53,857 (LY: 5-HT1C and 5-HT2 antagonist) (1.5 mg.kg-1 i.p.). Drug effects were similar in male and female rats. The negative effects of QD administration on RUN-EXH were not attenuated by administration of the peripherally restricted antagonist, xylamidine tosylate (up to 200 ug.kg-1 i.p.). The results of this investigation indicated that fatigue during prolonged exercise can be influenced by direct pharmacological administration of a serotonergic agonist and antagonist and that the mechanisms underlying these effects are likely to be central (brain) in nature.