On the mechanism by which methylxanthines enhance apomorphine-induced rotation behaviour in the rat

Methylxanthines, such as caffeine and theophylline, potentiate the rotation behaviour induced by dopamine receptor agonists in rats with unilateral lesions of the nigro-striatal pathway. In the present study we have examined the possibility that interaction with central adenosine mechanisms could influence rotation behaviour. Under in vitro conditions adenosine and N6-phenylisopropyl-adenosine (PIA) stimulate cyclic AMP accumulation. This effect was enhanced by the phosphodiesterase inhibitor rolipram, but blocked by alkylxanthines such as caffeine, theophylline and, particularly, 8-phenyl-theophylline. Rotation behaviour induced by apomorphine (0.05 mg/kg), was inhibited by PIA and rolipram and by a low dose of the adenosine deaminase inhibitor EHNA (2 mg/kg). By contrast, theophylline and 8-phenyl-theophylline caused a potentiation. The former drug stimulated rotation behaviour per se, while the latter did not. 8-Phenyl-theophylline entered the brain poorly and its concentration in brain it was less than 1/10 of theophylline. It is concluded that theophylline does not potentiate rotation behaviour secondarily to inhibition of phosphodiesterase. Antagonism of endogenous adenosine may partly explain the effect of methylxanthines. Possibly, some as yet unknown mechanism may also contribute to the effects of xanthine-derivatives on rotation behaviour.