Previous studies have pointed out that L-DOPA can interact with D1 or D2 receptors independent of its conversion to endogenous dopamine. The present study was set to investigate whether L-DOPA modulates dopamine release from striatal nerve terminals, using a preparation of synaptosomes preloaded with [3H]DA. Levodopa (1 µM) doubled the K+-induced [3H]DA release whereas the D2/D3 receptor agonist pramipexole (100 nM) inhibited it. The L-DOPA-evoked facilitation was mimicked by the D1 receptor agonist SKF38393 (30–300 nM) and prevented by the D1/D5 antagonist SCH23390 (100 nM) but not the DA transporter inhibitor GBR12783 (300 nM) or the aromatic L-amino acid decarboxylase inhibitor benserazide (1 µM). Higher L-DOPA concentrations (10 and 100 µM) elevated spontaneous [3H]DA efflux. This effect was counteracted by GBR12783 but not SCH23390. Binding of [3H]SCH23390 in synaptosomes (in test tubes) revealed a dense population of D1 receptors (2105 fmol/mg protein). Both SCH23390 and SKF38393 fully inhibited [3H]SCH23390 binding (Ki 0.42 nM and 29 nM, respectively). L-DOPA displaced [3H]SCH23390 binding maximally by 44% at 1 mM. This effect was halved by addition of GBR12935 and benserazide. We conclude that L-DOPA facilitates exocytotic [3H]DA release through SCH23390-sensitive D1 receptors, independent of its conversion to DA. It also promotes non-exocytotic [3H]DA release, possibly via conversion to DA and reversal of DA transporter. These data confirm that L-DOPA can directly interact with dopamine D1 receptors and might extend our knowledge of the neurobiological mechanisms underlying L-DOPA clinical effects.

L-DOPA promotes striatal dopamine release through D1 receptors and reversal of dopamine transporter

Morari M.
2021

Abstract

Previous studies have pointed out that L-DOPA can interact with D1 or D2 receptors independent of its conversion to endogenous dopamine. The present study was set to investigate whether L-DOPA modulates dopamine release from striatal nerve terminals, using a preparation of synaptosomes preloaded with [3H]DA. Levodopa (1 µM) doubled the K+-induced [3H]DA release whereas the D2/D3 receptor agonist pramipexole (100 nM) inhibited it. The L-DOPA-evoked facilitation was mimicked by the D1 receptor agonist SKF38393 (30–300 nM) and prevented by the D1/D5 antagonist SCH23390 (100 nM) but not the DA transporter inhibitor GBR12783 (300 nM) or the aromatic L-amino acid decarboxylase inhibitor benserazide (1 µM). Higher L-DOPA concentrations (10 and 100 µM) elevated spontaneous [3H]DA efflux. This effect was counteracted by GBR12783 but not SCH23390. Binding of [3H]SCH23390 in synaptosomes (in test tubes) revealed a dense population of D1 receptors (2105 fmol/mg protein). Both SCH23390 and SKF38393 fully inhibited [3H]SCH23390 binding (Ki 0.42 nM and 29 nM, respectively). L-DOPA displaced [3H]SCH23390 binding maximally by 44% at 1 mM. This effect was halved by addition of GBR12935 and benserazide. We conclude that L-DOPA facilitates exocytotic [3H]DA release through SCH23390-sensitive D1 receptors, independent of its conversion to DA. It also promotes non-exocytotic [3H]DA release, possibly via conversion to DA and reversal of DA transporter. These data confirm that L-DOPA can directly interact with dopamine D1 receptors and might extend our knowledge of the neurobiological mechanisms underlying L-DOPA clinical effects.
2021
File in questo prodotto:
File Dimensione Formato  
BRAINRES-D-21-00086_R1.pdf

non disponibili

Tipologia: Preprint (submitted version)
Licenza: Accesso privato - non pubblico
Dimensione 2.36 MB
Formato Adobe PDF
2.36 MB Adobe PDF Visualizza/Apri   Richiedi una copia
Pubblicazioni consigliate

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/3507706
Citazioni
  • ???jsp.display-item.citation.pmc??? 6
  • Scopus 9
  • ???jsp.display-item.citation.isi??? 8
  • OpenAlex ND
social impact