To further examine the effects of prenatal methylazoxymethanol (MAM) treatment on striatal dopaminergic systems, the status of presynaptic dopamine transporters was examined by quantitative autoradiography of [3H]GBR 12935 binding. Significantly higher [3H]GBR 12935 binding was seen in MAM-lesioned striatum in comparison to the controls, indicating relative dopaminergic hyperinnervation in MAM-induced hypoplastic striatum. The effect of prenatal MAM treatment on extracellular levels of dopamine and its metabolites in the striatum was also examined using in vivo microdialysis. As measured in conscious freely-moving rats, prenatal MAM treatment significantly increased basal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) release in the striatum in comparison with control rats. These data suggest that in accordance with morphological dopaminergic hyperinnervation, dopaminergic functions are significantly augmented in MAM-lesioned brains. Thus, it is suggested that MAM-induced microencephalic rats should serve as a good animal model for the study of augmented dopaminergic functions in the striatum.