Effects of chronic social defeat on expression of dopamine β-hydroxylase in rat brains

Abstract

It is documented that stress activates the locus coeruleus-norepinephrine system. However, there are far few reports regarding effects of stress on the expression of dopamine β-hydroxylase, a hallmark enzyme of the noradrenergic neuron. In the present study, adult Fischer 344 rats were subjected to chronic social defeat for 4 weeks. Dopamine β-hydroxylase expressional levels in the locus coeruleus and its terminal regions were measured by in situ hybridization and western blotting. The results showed that immediately following chronic social defeat there are significantly increased mRNA and protein levels of dopamine β-hydroxylase in the locus coeruleus, and dopamine β-hydroxylase protein levels in the hippocampus, frontal cortex and amygdala, compared with those in the control. This chronic social defeat-induced upregulation of dopamine β-hydroxylase was completely abolished by adrenalectomy, and/or by treatment with corticosteroid receptor antagonists, mifepristone and spironolactone, either alone or in combination. Furthermore, treatment with desipramine, an antidepressant with specific inhibitory effects on norepinephrine transport, prevented an increased dopamine β-hydroxylase expression by chronic social defeat in the locus coeruleus and its main terminal regions such as the hippocampus, frontal cortex and amygdala. However, treatment with fluoxetine, an antidepressant with specific inhibition for serotonin transport, only selectively blocked increased dopamine β-hydroxylase protein levels in the hippocampus caused by CSD. The present findings indicate that chronic social defeat activates the locus coeruleus-norepinephrine system by upregulating the expression of dopamine β-hydroxylase, which may increase norepinephrine synthesis. This chronic social defeat induced upregulation of DBH expression was mediated through corticosterone and corticosteroid receptors, with possible interference from antidepressants.

Fig. 1.

Effects of chronic social defeat (CSD) stress, and CSD plus treatment with desipramine or fluoxetine on plasma corticosterone concentrations (A, n = 8/group) and sucrose consumption (B, n = 8/group). The trunk blood was collected on the 28th day immediately after the end of last session of CSD. *P < 0.01, compared with the control; † P < 0.01, compared with the corresponding time point in the control group. Con, control; CSD/DMI, CSD plus treatment with desipramine; CSD/Flx, CSD plus treatment with fluoxetine.

Fig. 2.

Effects of CSD, adrenalectomy (A), and treatment with desipramine or fluoxetine (B), as well as with corticosteroid receptor antagonists (C) on DBH mRNA in the LC. Upper panel: DBH mRNA in LC tissues of rats detected by in situ hybridization (n = 7/group). Coronal brain sections were taken at 9.7 mm posterior from bregma (corresponding to Plate 58 in the brain atlas) (Paxinos and Watson, 2005). Lower panel: Quantitative analyses of mRNA in slides. * P < 0.05, compared with the control; † P < 0.05, compared with the CSD group;‡ P < 0.05, compared with the CSD/Flx group. ADX, adrenalectomy; Con, control; Sham, sham operation; CSD/ADX, CSD plus adrenalectomy; CSD/DMI, CSD plus treatment with desipramine; CSD/Flx, CSD plus treatment with fluoxetine; CSDM, CSD plus treatment with mifepristone; CSDS, CSD plus treatment with spironolactone; CSDMS, CSD plus treatment with mifepristone and spironolactone. Scale Bar: 50 μm.

Fig. 3.

Effects of CSD, adrenalectomy (A), treatment with desipramine or fluoxetine (B), and with corticosteroid receptor antagonists (C) on DBH proteins in the LC. The upper figures in A, B, and C show autoradiographs obtained by western blotting of DBH in the LC (n = 6–8/group). The lower graphs in A, B, and C show quantitative analysis of band densities. Values of DBH bands were normalized to those of β-actin probed on the same blot. *P < 0.05, compared with the control group; † P < 0.05, compared with the CSD group. See Figure 2 for abbreviations.

Fig. 4.

Effects of CSD and treatment with corticosteroid receptor antagonists on DBH-immunoreactivity in the LC. The top panels are representative micrographs of DBH immunofluorescence in the LC region from experimental rats. The bottom panels show measurements of the area fraction of DBH immunofluorescence in the LC region (n = 6/group). *P < 0.01, compared with the control. See Figure 2 for abbreviations. Scale Bar: 50 μm.

Fig. 5.

Effects of CSD and adrenalectomy (ADX) on DBH protein levels in the hippocampus (HP), frontal cortex (FC) and amygdala (Amy). The image figures show autoradiographs obtained by western blotting of DBH in different regions (n = 6–8/group). The lower graph shows quantitative analysis of band densities. Values of DBH bands were normalized to those of β-actin probed on the same blot. *P < 0.01, compared with the control group. †P < 0.05, ††P < 0.01, compared with the CSD group. See Figure 2 for abbreviations.

Fig. 6.

Effect of CSD and treatment with desipramine or fluoxetine on DBH protein levels the hippocampus (HP), frontal cortex (FC) and amygdala (Amy). The image figures show autoradiographs obtained by western blotting of DBH in different regions (n = 6–8/group). The lower graph shows quantitative analysis of band densities. Values of DBH bands were normalized to those of β-actin probed on the same blot. *P < 0.01, compared with the control group. †P < 0.05, compared with the CSD group. See Figure 2 for abbreviations.

Fig. 7.

Effect of CSD and treatment with corticosteroid receptor antagonists on DBH protein levels the hippocampus (HP), frontal cortex (FC) and amygdala (Amy). The image figures show autoradiographs obtained by western blotting of DBH in different regions (n = 6–8/group). The lower graph shows quantitative analysis of band densities. Values of DBH bands were normalized to those of β-actin probed on the same blot. *P < 0.01, compared with the control group. †P < 0.01, compared with the CSD group. See Figure 2 for abbreviations.