The use of tetrodotoxin for the characterization of drug-enhanced dopamine release in conscious rats studied by brain dialysis.

The effect of TTX (infused during brain dialysis of the striatum and nucleus accumbens) on the in vivo release of dopamine, 3,4-dihydroxyphenylacetic acid and homovanillic acid, was investigated. In addition it was studied whether the increase in the release of dopamine, induced by various pharmacological treatments, was sensitive to TTX infusion. The following drugs were studied: haloperidol, amphetamine, haloperidol co-administered with GBR 12909, morphine and MPP+. Dialysis was carried out in the striatum, except for morphine, which was studied in the nucleus accumbens. The infusion of TTX revealed three different types of pharmacologically enhanced dopamine release in conscious rats. First, action potential dependent dopamine release (exocytosis), which was observed in untreated animals as well as in animals treated with haloperidol, haloperidol + GBR 12909, and morphine. Second, action potential independent release (carrier-mediated) was established in the case of amphetamine. Third, action potential independent DA release, probably caused by neurotoxic reactions was observed during MPP+ infusion.