Fetal mesencephalic grafts influence the dopamine release in the non-lesioned striatum of 6-OHDA-lesioned rats: a behavioral and in vivo voltammetric study.

This study was performed to investigate the effect of intraventricular fetal mesencephalic grafts on the non-lesioned nigro-striatal system of rats with unilateral lesions of dopaminergic neurones in the medial forebrain bundle and to analyze the involvement of the non-lesioned side in functional recovery due to grafts in this model. Grafts placed to the lesioned striatum produced a continuous decrease of apomorphine (APO, 0.25 mg/kg intraperitoneally (i.p.)) and amphetamine (AMPH, 5 mg/kg, i.p.) induced rotations over 7 months after grafting. Using differential pulse voltammetry (DPV) in anaesthetized and pargyline (75 mg/kg, i.p.) pretreated rats we found that 8 months after grafting in the lesioned striatum AMPH (5 mg/kg, i.p.) produced a higher increase of the dopamine (DA) signal (i.e., it became measurable), whereas in the non-lesioned striatum the same treatment produced a smaller increase of the DA signal, both compared to that in sham-grafted controls. After grafting onto the non-lesioned striatum, only a slight decrease of APO-induced rotations was observed, whereas AMPH-induced rotations were increased. In these animals AMPH did not produce a measurable DA signal in the lesioned striatum. The DA signal in the non-lesioned striatum was slightly higher than that of non-grafted controls. These results show clearly that unilateral fetal mesencephalic grafts producing behavioural recovery in the unilateral 6-OHDA model of the rat produce changes at dopaminergic mechanisms in the non-lesioned striatum.