Some factors affecting striatal 3-methoxytyramine concentrations in the mouse and rat

Apomorphine, a DA agonist, at a dose of 2 mg/kg, produced a rapid decline in 3-MT concentrations in the rat striatum; this is consistent with a reduction in the firing rate of nigrostriatal neurons. The injection of a 12.5 mg/kg dose of phenylethylamine transiently increased 3-MT concentrations in the mouse striatum. A more profound increase was produced by this dose in the rat striatum. Cocaine (5 mg/kg) produced a decrease in DOPAC concentrations in both species thus suggesting that the re-uptake of DA from the synaptic cleft in both species was very similar. Amfonelic acid, however, produced a different profile in each species. The concentration of 3-MT is larger in the mouse striatum as a result of several possible mechanisms: the higher percentage of MAO isoenzyme B in the mouse brain (3-MT is a preferred substrate of MAO isoenzyme A) and/or due to differences in the clearance mechanisms for 3-MT produced extraneuronally - with the mouse having a less avid clearance system either for DA or for 3-MT.