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Keywords:

  • Adenosine;
  • Striatum;
  • Motor Incoordination;
  • ADP Ribosylation;
  • Pertussis Toxin

Background: We demonstrated previously that striatal adenosine modulates ethanol-induced motor incoordination (EIMI) via adenosine A1 receptors coupled to pertussis toxin (PT)-sensitive G protein and adenylyl cyclase-cyclic adenosine monophosphate (cAMP). Additionally, intrastriatal (IST) PT antagonizes EIMI and its potentiation by the adenosine A1 agonist N6-cyclohexyladenosine; it also inhibits cAMP concentration.

Methods: Guide cannulas were stereotaxically implanted for IST pretreatment with PT followed 5 days later by IST of N6-cyclohexyladenosine and intraperitoneal ethanol. The adenosine diphosphate (ADP) ribosylation reaction involved PT-catalyzed [32P]nicotinamide adenine dinucleotide (NAD) labeling of rat striatal membranes. Antagonism of EIMI (Rotorod method) after IST microinfusion of PT was investigated to determine whether it was due to a decrease in the functional activity of G proteins due to ADP ribosylation of the G subunit caused it.

Results: Striatal membranes from IST PT (0.5 μg)–treated animals exhibited significantly attenuated (up to 90%) in vitro ADP ribosylation with [32P]NAD. Striatal membranes from animals injected with ethanol (1.5 g/kg intraperitoneally) exhibited statistically significant increase (11%) in in vitro ADP ribosylation. Similarly, ethanol (50 mM) added to striatal membranes from untreated animals produced significant stimulation of in vitro ADP ribosylation. The decrease in the functional activity of G proteins due to ADP ribosylation of the G subunit after IST PT was functionally correlated with marked attenuation in EIMI, as observed previously. This finding suggests a blockade of functional activity of PT-sensitive striatal Gi/Go proteins (i.e., fewer available sites for labeled NAD incorporation). The in vivo ethanol results indicate that it must have caused an increase in the ribosylation capacity of G in vivo (i.e., increased Gi activity). Increased ADP ribosylation by in vitro ethanol increases Gi/Go activity, consistent with EIMI, as previously reported.

Conclusions: The results provide biochemical evidence of an ethanol-induced increase in ADP ribosylation of G causing a decrease in the functional activity of G proteins coupled via Gi/Go to adenylyl cyclase-cAMP. These results confirm the previously observed antagonism of EIMI by PT (IST).