GDNF PROTECTS NIGRAL DOPAMINE NEURONS AGAINST 6-HYDROXYDOPAMINE IN-VIVO

Glial cell line-derived neurotrophic factor (GDNF), a novel member of the TGF-beta superfamily, has been shown to promote the survival and m orphological differentiation of fetal dopamine neurons in culture and increase dopamine levels and metabolism in adult rats. Since several o ther trophic factors are able to rescue specific populations of mature CNS neurons following injury, the present study was designed to inves tigate a possible neuroprotective role by GDNF for midbrain dopamine n eurons in rats exposed to the neurotoxin 6-hydroxydopamine (6-OHDA). P rior to surgery, young adult male Fisher 344 rats were divided into th e following groups (n = 7-8/group): (1) intranigral saline + intranigr al 6-OHDA; (2) intranigral GDNF + intranigral 6-OHDA; (3) intranigral saline + intrastriatal 6-OHDA; and (4) intranigral GDNF + intrastriata l 6-OHDA. The saline treated groups received a single 2 mu l intranigr al injection of phosphate buffered saline (PBS) while the GDNF treated rats received 10 mu g/2 mu l GDNF in PBS. Twenty-four hours later, th e animals received a unilateral 4 mu g/mu l 6-OHDA infusion either int o the substantia nigra or striatum. The rats were sacrificed two weeks postsurgery and the brains processed for tyrosine hydroxylase (TH) im munocytochemistry. Representative TH immunoreactive (TH-IR) sections w ere also counterstained with hematoxylin and eosin to determine the to tal number of neurons remaining in the substantia nigra pars compacta and ventral tegmental area. In the nigral lesion groups, there was sig nificantly less loss of TH-IR neurons in the substantia nigra pars com pacta of GDNF (47% survival) vs. PBS (9% survival) treated animals. Th e same was true in the ventral tegmental area, where there was a 90% s urvival of TH-IR neurons in the GDNF treated animals as compared to a 68% survival in PBS treated animals. In the striatal lesion groups, th ere was significant sparing of TH-IR neurons in the substantia nigra p ars compacta of the GDNF (40% survival) compared to the PBS (16% survi val) treated animals. However, in the ventral tegmental area, the prot ection seen in the GDNF treated animals (69% survival) was not statist ically significant when compared to the PBS treated rats (48% survival ). In sections counter stained with hematoxylin and eosin, the percent age of neurons surviving in GDNF treated hosts was higher suggesting t hat the 6-OHDA toxicity may reduce TH expression in some dopamine neur ons without inducing cell death. Therefore, in both lesion models, our results demonstrate a substantial neuroprotective effect in rats pret reated with GDNF when compared to the vehicle treated groups.