Adenosine A1 and A2A receptor antagonists stimulate motor activity: evidence for an increased effectiveness in aged rats

The motor effects of selective adenosine A(1) and A(2A) receptor antagonists were tested in young (2 months) and aged (24 months) Wistar rats. In young rats, both the selective A(2A) receptor antagonist 5-amino-7-(2-phenylethy)-2-2(2-furyl)-pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine (SCH 58261, minimal effective dose 2 mg/kg intraperitoneally (i.p.)) and the selective Al receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT, minimal effective dose 1.2 mg/kg i.p.) stimulated motor activity. In old rats, both compounds induced significant motor activation starting from doses lower than those required in young animals. Specifically, the minimal effective doses of SCH 58261 and CPT in aged rats were 1 and 0.6 mg/kg i.p, respectively. The results indicate that both adenosine Al and A2A receptors play a functional role in the control of motor activity, and, therefore, the blockade of both receptor subtypes is involved in the motor stimulating properties of methylxanthines. Also the evidence indicates, for the first time, that in aged animals the motor inhibitory adenosinergic tone seems to be increased with respect to young animals. (C) 1998 Elsevier Science Ireland Ltd. AII rights reserved.