Time-course of the hypomotility effects of the adenosine analogues,cyclohexyladenosine and N-ethylcarboxamidoadenosine,in a holeboard test

Abstract

The time-course of the hypomotility effects of the adenosine analogues 5'-N- ethylcarboxamidoadenosine (NECA) and N⁶-cyclohexyladenosine (CHA) was investigated in a holeboard test. Behaviourally equipotent doses of both compounds given to independent groups of animals showed significant depression of both exploratory head-dipping and locomotor activity at the 9, 18 and 36 min time points after drug administration. No significant differences from control group values were detected at 72 or 144 min post-administration. Additionally, the effects of both analogues administered immediately before a holeboard test were examined by investigating four 2 min time bins over the 8 min test session. Significant drug x time bin interactions were detected: NECA and CHA both showed faster reductions in locomotor activity, and NECA more reduction in head-dipping, over the test as compared to control. However, no differences between NECA and CHA on test habituation were detected. The results of these experiments support the view that pharmacodynamic rather than phar macokinetic factors may be responsible for the different behavioural potencies of NECA and CHA.