title: The role of dopamine receptors in regulating the size of axonal arbors.
abstract: Factors that regulate terminal arbor size of substantia nigra pars compacta (SNpc) neurons during development and after injury are not well understood. This study examined the role of dopamine receptors in regulating arbor size. Terminal arbors were examined in mice with targeted deletion of the D1 or D2 dopamine receptor [D1(-/-) and D2(-/-) mice, respectively]. Terminal trees were also examined after treatment with receptor blockers and after partial SNpc lesions. Immunohistochemistry was performed, and the number of SNpc neurons and dopaminergic terminals in the striatum was estimated. The number of dopaminergic SNpc neurons were reduced in D1(-/-) and D2(-/-) mice. Density of dopaminergic terminals was unchanged in D1(-/-) mice and increased in D2 (-/-) mice. Steady-state striatal DA and DOPAC levels revealed that dopamine activity was enhanced in D2(-/-) mice but reduced in D1(-/-) mice. Two months after partial SNpc lesions, striatal terminal density was normal in both wild-type and D1(-/-) mice but reduced in D2(-/-) mice. Administration of DA receptor antagonists resulted in larger terminal arbors in D1(-/-) and wild-type mice, whereas D2(-/-) mice showed no change in terminal density. Functional blockade of the D2R during development or in the adult brain results in increased axonal sprouting. Partial SNpc lesions resulted in compensatory sprouting, only in mice with functional D2R. These results suggest that individual dopaminergic axons in D2(-/-) mice have reached maximal arbor size. We conclude that the D2 receptor may play a role in modulating the extent of the terminal arbor of SNpc neurons.
authors: Neurosciences Group, Department of Medicine and Department of Neurology, Monash Medical Center, Clayton 3168, Australia.
authors: C L
authors: CL
authors: Parish
authors: D I
authors: DI
authors: Finkelstein
authors: J
authors: J
authors: Drago
authors: E
authors: E
authors: Borrelli
authors: M K
authors: MK
authors: Horne
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D001369:Axons / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D002352:Carrier Proteins / Q000378:metabolism; D002452:Cell Count; D003342:Corpus Striatum / Q000166:cytology; D004298:Dopamine / Q000378:metabolism; D018492:Dopamine Antagonists / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists; D050483:Dopamine Plasma Membrane Transport Proteins; D006579:Heterozygote; D006720:Homozygote; D007150:Immunohistochemistry; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D051379:Mice; D008815:Mice, Inbred Strains; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins; D009434:Neural Pathways / Q000166:cytology; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016627:Oxidopamine / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D017447:Receptors, Dopamine D1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000378:metabolism*; D013378:Substantia Nigra / Q000166:cytology / Q000187:drug effects / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D050483:Dopamine Plasma Membrane Transport Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D017447:Receptors, Dopamine D1; D017448:Receptors, Dopamine D2; D015102:3,4-Dihydroxyphenylacetic Acid; D016627:Oxidopamine; D004298:Dopamine