title: Functional roles of dopamine D2 and D3 autoreceptors on nigrostriatal neurons analyzed by antisense knockdown in vivo.
abstract: Two different 19-mer antisense oligodeoxynucleotides complementary to the initial coding regions of dopamine D2 or D3 receptor mRNA were infused unilaterally into the substantia nigra of rats for 3-6 d to suppress synthesis of D2 and/or D3 receptors on substantia nigra dopaminergic neurons, thereby producing specific reductions of D2 and/or D3 receptors. Autoradiographic receptor binding revealed that D2 and D3 antisense oligodeoxynucleotides specifically and significantly reduced D2 or D3 binding in the ipsilateral substantia nigra, respectively, without affecting dopamine receptor binding in the neostriatum. Either D2 or D3 antisense oligodeoxynucleotides greatly attenuated the ability of apomorphine to inhibit dopaminergic neurons in vivo, an effect that was potentiated by simultaneous administration of D2 and D3 antisenses. Despite these effects, neither the rate nor the pattern of spontaneous activity of antisense-treated nigrostriatal neurons differed from those in the control groups. The proportion of antidromic responses consisting of full spikes from antisense-treated rats was significantly greater, and the mean antidromic threshold was significantly lower than in controls, indicating that autoreceptor knockdown increased both somatodendritic and terminal excitability. These data demonstrate that selective reduction of specific dopamine receptor subtypes by antisense infusion can be effected in vivo, and that nigrostriatal neurons express both D2 and D3 autoreceptors at their somatodendritic and axon terminal regions. Although the somatodendritic and terminal autoreceptors modulate dendritic and terminal excitability, respectively, the interaction of endogenously released dopamine with somatodendritic autoreceptors does not appear to exert a significant effect on spontaneous activity in anesthetized rats.
authors.affiliation: Center for Molecular and Behavioral Neuroscience, Aidekman Research Center, Program in Cellular and Molecular Biodynamics, Rutgers, The State University of New Jersey, Newark, New Jersey 07102, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Tepper
authors.forename: B C
authors.initials: BC
authors.lastname: Sun
authors.forename: L P
authors.initials: LP
authors.lastname: Martin
authors.forename: I
authors.initials: I
authors.lastname: Creese
mesh_terms: D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001345:Autoradiography; D001369:Axons / Q000187:drug effects / Q000502:physiology; D001483:Base Sequence; D003342:Corpus Striatum / Q000187:drug effects / Q000502:physiology*; D003712:Dendrites / Q000187:drug effects / Q000502:physiology; D018491:Dopamine Agonists / Q000378:metabolism; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D007839:Functional Laterality; D008297:Male; D009043:Motor Activity; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000502:physiology*; D050637:Receptors, Dopamine D3; D013378:Substantia Nigra / Q000187:drug effects / Q000502:physiology*; D013764:Tetrahydronaphthalenes / Q000378:metabolism; D014316:Tritium
chemical_list: D018491:Dopamine Agonists; C493595:Drd3 protein, rat; D020319:Oligodeoxyribonucleotides, Antisense; D012333:RNA, Messenger; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; D013764:Tetrahydronaphthalenes; D014316:Tritium; D001058:Apomorphine; C031349:7-hydroxy-2-N,N-dipropylaminotetralin