title: GDNF enhances the synaptic efficacy of dopaminergic neurons in culture.
abstract: Glial cell line-derived neurotrophic factor (GDNF) is known to promote the survival and differentiation of dopaminergic neurons of the midbrain. GDNF also causes an enhancement of dopamine release by a mechanism which is presently unclear. Using isolated dopaminergic neurons of the rat ventral tegmental area in culture, we have tested the hypothesis that GDNF regulates the establishment and functional properties of synaptic terminals. Previous studies have shown that single dopaminergic neurons in culture can co-release glutamate in addition to dopamine, leading to the generation of a fast excitatory autaptic current via glutamate receptors. Using excitatory autaptic currents as an assay for the activity of synapses established by identified dopaminergic neurons, we found that chronically applied GDNF produced a threefold increase in the amplitude of excitatory autaptic currents. This action was specific for dopaminergic neurons because GDNF had no such effect on ventral tegmental area GABAergic neurons. The enhancement of excitatory autaptic current amplitude caused by GDNF was accompanied by an increase in the frequency of spontaneous miniature excitatory autaptic currents. These observations confirmed a presynaptic locus of change. We identified synaptic terminals by using synapsin-1 immunofluorescence. In single tyrosine hydroxylase-positive neurons, the number of synapsin-positive puncta which represent putative synaptic terminals was found to be approximately doubled in GDNF-treated cells at 5, 10 and 15 days in culture. The number of such morphologically identified terminals in isolated GABAergic neurons was unchanged by GDNF. These results suggest that one mechanism through which GDNF may enhance dopamine release is through promoting the establishment of new functional synaptic terminals.
authors.affiliation: Départements de Pharmacologie et de Psychiatrie, Centre de Recherche en Sciences Neurologiques, Centre de Recherche Fernand Seguin, Université de Montréal, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Bourque
authors.forename: L E
authors.initials: LE
authors.lastname: Trudeau
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004298:Dopamine / Q000502:physiology*; D029721:Drosophila Proteins; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D005455:Fluorescent Antibody Technique; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008562:Membrane Glycoproteins / Q000032:analysis; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D026901:Membrane Transport Proteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins / Q000494:pharmacology*; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D009479:Neuropeptides; D018696:Neuroprotective Agents / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051096:Proto-Oncogene Proteins c-ret; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology; D013569:Synapses / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D016704:Synapsins / Q000032:analysis; D016708:Synaptophysin / Q000032:analysis; D017557:Ventral Tegmental Area / Q000166:cytology; D050492:Vesicular Biogenic Amine Transport Proteins; D005680:gamma-Aminobutyric Acid / Q000502:physiology
chemical_list: D029721:Drosophila Proteins; C495041:Gdnf protein, rat; D051100:Glial Cell Line-Derived Neurotrophic Factor; D051097:Glial Cell Line-Derived Neurotrophic Factor Receptors; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009414:Nerve Growth Factors; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D018696:Neuroprotective Agents; D011518:Proto-Oncogene Proteins; D016704:Synapsins; D016708:Synaptophysin; D050492:Vesicular Biogenic Amine Transport Proteins; D005680:gamma-Aminobutyric Acid; D051096:Proto-Oncogene Proteins c-ret; D020794:Receptor Protein-Tyrosine Kinases; C416649:Ret protein, Drosophila; D004298:Dopamine