Glial cell line-derived neurotrophic factor: Distribution and pharmacology in the rat following a bolus intraventricular injection

Glial cell line-derived neurotrophic factor (GDNF) has been shown to increase dopaminergic parameters in vitro and in vivo and can reduce parkinsonian behaviors in animal models of the disease. This study determined the potential of the lateral ventricle as an administration route for GDNF by examining the distribution and neurochemical consequences of a single intraventricular injection. Autoradiographic analysis showed that intraventricularly administered [I-125]GDNF was distributed throughout the ventricular system at 1 and 24 h following injection. The cerebral cortex, septum, diagonal band, fimbria, striatum, hippocampus, hypothalamus, substantia nigra/ventral tegmental area, and cerebellum were also labeled. At 7 days, there was still labeling throughout the ventricular system, hypothalamus, substantia nigra, and cerebellum. Twenty-four hours following an intrastriatal injection of [I-125]GDNF, label was observed in the substantia nigra/ventral tegmental area, demonstrating retrograde transport. The neurochemical effects of intraventricularly administered GDNF (0.1-100 mu g) at 7 days post injection were also examined. GDNF significantly increased striatal (approximately 28%) and nigral (up to 40%) dopamine, as well as regulated the dopamine metabolites homovanillic acid and dihydroxyphenylacetic acid. Dopamine levels were unchanged in the frontal cortex. Dopamine content was significantly increased in the hypothalamus (up to 35%), an increase which may contribute to the inhibition of weight gain seen after administration of GDNF. Additionally, dopamine turnover was decreased or unchanged across the brain regions analyzed, which may indicate that in unlesioned rats, intraventricularly administered GDNF stimulates the synthesis and storage of dopamine. This study shows that intraventricularly injected GDNF can access basal ganglia structures, most notably the midbrain dopamine cell body region, and remains present in this area for at least 7 days following a single administration. GDNF differentially increases dopaminergic tone within a variety of brain structures, including the nigrostriatal pathway. These data support the potential effectiveness of intraventricular administered GDNF as a treatment for Parkinson's disease.