gms | German Medical Science

Objective: Ventral mesencephalic (VM) grafts of E14 rat embryos, implanted into the striatum (STR) in the 6-hydroxydopamine (6-OHDA) medial forebrain bundle (MFB) rat model of Parkinson’s disease (PD) can restore dopamine (DA) in the transplanted area. Ectopic graft placement is necessary due to the inability of VM grafts in the substantia nigra (SN) to reinnervate the lesioned STR in the adult 6-OHDA rat model. In the neonatal rat model, graft-derived axonal outgrowth can be observed. Here, we investigate the impact of the host's age on axonal outgrowth of VM cells implanted into the SN in the neonatal 6-OHDA rat model. Further, expression of genes involved in axonal outgrowth is analyzed with respect to their role in transplant fiber outgrowth.

Methods: Rats were bilaterally lesioned by injection of 6-OHDA on P1 and received E14 VM grafts on P10, P11, P12, P13, P15, & P18 into the right SN. Rotational behavior was assessed until 3 months after surgery. Injection of the retrograde tracer FluroGold (FG) into the right STR was performed and grafts were evaluated by immunohistochemistry (IHC). Gene expression of NogoA and Semaphorin3A (Sema3A) was analyzed in the neonatal 6-OHDA model. A combined method of in situ hybridization and double fluorescent IHC was performed to analyze expression in glia along the MFB in lesioned and control animals.

Results: Animals that received a graft on P10, P11& P12 showed significant (p<0.05) rotational bias induced by apomorphine when compared to all other groups. Amphetamine-induced rotation revealed significant differences on P10 & P11. Stereological analyses of the grafts revealed similar cell distribution patterns in all groups. Significant DA cell survival (p<0.05) and fiber outgrowth from SN to STR was observed in the P10 group. Retrograde tracer experiments showed a high number of TH+ cells co-expressing FG in the P10 group. NogoA expression was neither different between control and lesioned animals, nor across different postnatal days. Reduced expression in the SN was due to bilateral lesion, as indicated by TH co-expression. Expression of Sema3A was increased in the STR in P15 lesioned brains compared to controls, which was not detected at earlier time points.

Conclusions: Concerning fiber outgrowth the benefit of grafting depends on host age and is best when transplantation is performed early. The potential of E14 VM grafts in the SN to extend axons to the STR is determined by developmental cues expressed during early postnatal age.