Dynamic changes of striatal dopamine D ₂ receptor binding at later stages after unilateral lesions of the medial forebrain bundle in Parkinsonian rat models

Our previous study regarding the changes of D ₂ receptor in nigrostriatal dopamine system at an early stage (4 weeks after lesion) indicated a different functional activity of striatal D ₂ receptor between two different rat parkinsonian models, lesioning with 6-hydroxydopamine in the striatum and in the medial forebrain bundle (MFB). In the present study, we further examined binding of D ₂ receptor as well as pre-synaptic dopamine transporter (DAT) at later stages (6 months after lesion) both in the striatal and MFB lesion models. The D ₂ receptor binding in MFB model at 6 months after lesion was significantly lower than that at 4 weeks after lesion, albeit it was still higher than the normal side. The D ₂ receptor binding in striatal model was decreased to the same extent at both 4 weeks and 6 months after lesion. DAT binding decreased at 6 months after lesion, more profound in MFB model, and the degree of reduction was not different from that at 4 weeks after lesion. These findings indicated different dynamic processes of the D ₂ receptor and DAT during a longer time observation in the striatal and MFB lesion models. The dynamic changes of D ₂ receptor activity after lesion should be considered when selecting 6-hydroxydopamine-induced rat parkinsonian models.