Effect of the beta(2)-agonist clenbuterol on the locomotor activity of ratsubmitted to a 14-day period of hypodynamia-hypokinesia

The beta (2)-adrenergic agonist clenbuterol is known for its anabolic actio n on normal and atrophied muscles. The aim of this work was to evaluate if chronic clenbuterol administration could prevent alterations in the locomot or activity induced by hindlimb suspension. The effects of clenbuterol were evaluated in three studies: muscle morphological characteristics, observat ion of locomotor movement and electromyographic activity of soleus and gast rocnemius muscles. Rats were divided into four groups: control (CON, morpho logical study only), hindlimb suspended (HS), clenbuterol administered (CB, 2 mg kg(-1) per day in drinking water), and hindlimb suspended + clenbuter ol administered (HSCB). The soleus muscle weight was reduced in the two sus pended groups (HS and HSCB) but did not change after clenbuterol treatment. By contrast, the gastrocnemius weight was not affected by suspension but w as increased by clenbuterol (CB and HSCB). Some locomotor deficits were alw ays observed in HS rats (unstable gait, ankle hyperextension,...). Clenbute rol administration did not prevent these perturbations. Cycle duration and soleus burst duration were increased in the three groups. Soleus mean EMG ( burst area/duration) was decreased in HS rats, but not in the two other gro ups. For the gastrocnemius, burst duration was increased in CB rats, decrea sed in HSCB rats and unchanged in HS ones; mean EMG did not change. In conc lusion: clenbuterol cannot be used as a countermeasure to reduce the altera tion in locomotor performance. Moreover, our results suggest that this alte ration is specifically related to changes in neuronal properties. (C) 2001 Elsevier Science B.V. All rights reserved.