The imidazoline receptor ligand 2-(2-benzofuranyl)-2-imidazoline is a dopamine-releasing agent in the rat striatum in vivo.

2-BFI (2-(2-benzofuranyl)-2-imidazoline) is a prototypical I2-imidazoline receptor ligand. In vivo, however, 2-BFI (1-20 mg/kg) decreased the synthesis of dopa/dopamine (DA) in rat striatum through mechanisms not related to interaction with I2-imidazoline receptors or to inhibition of the enzyme monoamine oxidase. The aim of this study was to unravel the mechanism underlying this potent effect of 2-BFI in brain. In vitro 2-BFI showed very low affinity for D2-dopamine receptors (K(i)=47 microM), and in vivo the drug (7 mg/kg) decreased the synthesis of striatal dopa/DA similarly in control rats (43%) and in rats pre-treated with alpha-methyl-para-tyrosine (50%) or cocaine (51%), indicating that this effect was not the result of D2-dopamine autoreceptor direct stimulation, inhibition of the enzyme tyrosine hydroxylase or blockade of neuronal DA reuptake. In DA-depleted (reserpine-treated) rats, however, 2-BFI did not inhibit significantly (11%), the synthesis of dopa/DA in the striatum, indicating that the effect of 2-BFI was indirectly mediated by endogenous DA through the activation of D2-dopamine autoreceptors. In conclusion, the I2-imidazoline receptor ligand 2-BFI is also a DA releasing agent in brain, and consequently a DA indirect agonist in vivo.