Effect of ethanol on cyclic nucleotides in vivo: consequences of controlling motor and respiratory changes

Many psychotropic drugs alter cerebellar cyclic guanosine-3',5'-monophosphate (cGMP) content. Whereas apomorphine increased levels, central depressants such as ethanol, chlordiazepoxide or barbiturates, reduce the content of cerebellar cGMP without altering levels of cyclic adenosine-3',5'-monophosphate (cAMP). Additional data indicate that tolerance develops to this reduction of cerebellar cGMP by ethanol. In paralyzed animals, the increase in cerebellar cGMP content induced by apomorphine and the decrease caused by ethanol were dramatically attenuated. Since relatively high doses of ethanol were needed to decrease blood CO2 tension in spontaneously moving rats, changes in respiratory function appear to be of only minor importance in the ethanol-induced decrease in cerebellar cGMP. It is concluded that ethanol-induced changes in content of cerebellar cGMP in vivo may be secondary to alterations in motor and, to a lesser extent, in respiratory function.