Correlation of telemetered heart rate and locomotor behavior in cyclazocine treated rats

Two experiments were performed to verify the validity of a biotelemetry system for 24 hour recording of heart rate (HR) of rats in behavioral toxicology. As test substance the hallucinogenic drug cyclazocine was used at various dose levels (0.1, 0.75, 1.5 and 3.0 mg/kg SC). In a first experiment, female rats were tested in their home cage. It was found that HR was altered by cyclazocine during the four hours following drug injection. This alteration was biphasic: immediately after injection, when control HR was high, cyclazocine lowered HR. In contrast, one hour after the injection, when control HR was low, cyclazocine increased HR. The duration of this increase of HR was dose-dependent, while the magnitude was not. In a second experiment male rats were tested in a residential maze: simultaneously to the rat's HR, locomotor activity was recorded. The results of the first experiment were confirmed and extended to males as well as to a different environmental situation. The additional behavioral data showed a different aspect of cyclazocine action: 0.75 mg/kg initially decreased and later increased activity while 3.0 mg/kg first did not alter activity and later increased it, leading to a dissociation between HR and activity. The findings demonstrate that recording of HR adds a new dimension to the data obtained in conventional behavioral tests. The results are discussed with regard to behavioral and neurochemical effects of the drug.