Sedative and anticonvulsant effects of adenosine analogs in mouse and rat

The behavioral and physiological effects of L-phenylisopropyladenosine, cyclohexyladenosine and 2-chloroadenosine were examined in mice and rats. These analogs of adenosine are agonists which bind with high affinity to putative central A1 receptors in vitro. Relatively low doses of these drugs administered i.p. produced marked sedation and hypothermia; higher doses resulted in an almost complete cessation of spontaneous motor activity as well as some ataxia. These analogs also antagonized seizures elicited by a variety of convulsants with different mechanisms of action. The differences observed in the anticonvulsant potencies of the analogs suggest that these effects are not produced by the interaction of these drugs with a single class of adenosine receptor. In particular, 2-chloroadenosine and cyclohexyladenosine appear to be more related to each other pharmacologically than to L-phenylisopropyladenosine. Because some of the anticonvulsant actions of L-phenylisopropyladenosine are not reversed by the adenosine antagonist theophylline, and are not shared by the other analogs, these may reflect actions mediated by other, perhaps nonpurinergic receptors. Although benzodiazepines also have sedative, hypothermic and anticonvulsant properties, responses to benzodiazepines can be clearly dissociated from responses to the adenosine agonists.