Striatal GDNF System Elicits Chemoattraction to RET Positive Dopamine Axons Seven Times Longer in Distance than the Abundant Medium Spiny Neurons and Covers Approximately One Twelfth of the Striatal Neuronal Volume

Abstract

Glial cell line-derived neurotrophic factor GDNF is among the strongest dopamine neuron function and survival promoting factors known. Due to this reason, it has clinical relevance in dopamine disorders such as Parkinson’s disease and Schizophrenia. In the striatum, GDNF is exclusively expressed in interneurons which make up only about 0.6% of striatal cells. Despite clinical significance, histological analysis of striatal GDNF system arborization and relevance to incoming dopamine axons, which bear its receptor RET, has remained enigmatic. This is mainly due to the lack of antibodies able to visualize GDNF and RET positive cellular processes; here we overcome this problem by using knock-in marker alleles. We find that GDNF neurons chemoattract RET+ axons at least 7 times longer in distance than medium spiny neurons (MSNs), which make up 95% of striatal neurons. Furthermore, we provide evidence that tyrosine hydroxylase, the rate limiting enzyme in dopamine synthesis, is enriched towards GDNF neurons in the dopamine axons. Finally, we find that GDNF neuron arborizations occupy approximately twelve times less striatal volume than 135 times more abundant MSNs. Collectively, our results improve our understanding of how endogenous GDNF affects striatal dopamine system function.