Estrogen receptors and lesion-induced response of striatal dopamine receptors

Neuroprotection by 17β-estradiol and an estrogen receptor (ER) agonist against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesion were shown to implicate protein kinase B (Akt) signaling in mice. In order to evaluate the associated mechanisms, this study compared estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) intact or knockout (KO) and wild-type (WT) C57Bl/6 male mice following MPTP treatment of 7, 9, 11 mg/kg and/or 17β-estradiol. Striatal D1 and D2 dopamine (DA) receptors were measured by autoradiography with the specific ligands [3H]-SCH 23390 and [3H]-raclopride, respectively and signaling by Western blot for Akt, glycogen synthase kinase 3β (GSK3β) and extracellular-regulated signal kinases (ERK1 and ERK2). Control ERKOβ mice had lower striatal [3H]-SCH 23390 specific binding than WT and ERKOα mice; both KO mice had lower [3H]-raclopride specific binding. Striatal D1 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in ERKOα mice and remained unchanged in WT and ERKOβ mice. Striatal D2 receptors decreased with increasing doses of MPTP in correlation with striatal DA concentrations in WT and ERKOα mice and increased in ERKOβ mice. In MPTP-lesioned mice, 17β-estradiol treatment increased D1 receptors in ERKOα and ERKOβ mice and D2 receptors in WT and ERKOβ mice. MPTP did not affect striatal pAkt/Akt and pGSK3β/GSK3β levels in WT and ERKOα mice, while in vehicle-treated ERKOβ mice these levels were higher and increased with MPTP lesioning. Striatal pERK1/ERK1 and pERK2/ERK2 levels showed to a lesser extent a similar pattern. In conclusion, ERs affected the response of striatal DA receptors to a MPTP lesion and post receptor signaling.

► MPTP increased striatal D2 receptor levels in ERKOβ but not in ERKOα or WT mice. ► Striatal DA levels correlated with D1 and D2 receptors with genotype specificity. ► 17β-E2 increased D1 in MPTP ERKO mice and D2 receptors in WT and ERKOβ mice. ► MPTP did not affect striatal pAkt, pGSK3β, pERK1 and pERK2 in WT and ERKOα mice. ► In intact ERKOβ mice, these levels were higher and increased with MPTP lesioning.