Suppression of sucrose drinking by chronic mild unpredictable stress: A methodological analysis

Clinical investigations present much evidence that the glucocorticoid receptor (GR) antagonist mifepristone leads to a rapid amelioration of depression. The molecular mechanisms of mifepristone involved in the treatment of depression are not fully understood. Depression is associated with hippocampal plasticity, for which increased excitatory amino acid (EAA) release in CA3 induced by chronic stress is responsible, and glucocorticoids have a permissive role and act synergistically with EAAs in producing neuronal damage. Moreover, glucocorticoids increase synapsin I, which has a key role in the release of neurotransmitter, including EAAs. Hereby, we hypothesize that major depression involves synapsin I alteration and that mifepristone blocks this alteration. In the present study, we observed both the expression of hippocampal synapsin I and depression-associated behavior in a rat model of depression induced by chronic unpredictable mild stress (CUMS). The result showed that a region-dependent synapsin I alteration occurs in the rat hippocampus after 21 days of CUMS, that is, it increases in dentate gyrus (DG)/CA3 and decreases in the CA1 region. Correlation analysis indicated that the decrease of synapsin I in CA1 is highly correlated with the increase in the DG/CA3 subfield. Simultaneously, the region-dependent alteration of synapsin I is correlated with depression-associated behaviors. Both the alteration of synapsin I and the depression-associated behavior were rapidly restored after treatment with mifepristone for 1 week. The result suggests that the molecular mechanism underlying the treatment of depression with mifepristone is associated with the rapid repair of the synaptic alteration.

Section: Discussionmentioning

confidence: 75%

Mifepristone Repairs Region-Dependent Alteration of Synapsin I in Hippocampus in Rat Model of Depression

Han

Wang

et al. 2007

“…In this model, sucrose intake is considered a valid measure of sensitivity to reward and it is assumed, that CMS causes a generalized decrease in reward sensitivity Muscat and Willner, 1992;Willner et al, 1992Willner et al, , 1996Willner, 1984Willner, , 1997Willner, , 2005.…”

Section: Discussionmentioning

confidence: 99%

Hippocampal Cytogenesis Correlates to Escitalopram-Mediated Recovery in a Chronic Mild Stress Rat Model of Depression

Jayatissa

Bisgaard

Tingström

et al. 2006

324

205

From clinical studies it is known that recurrent depressive episodes associate with a reduced hippocampal volume. Conversely, preclinical studies have shown that chronic antidepressant treatment increases hippocampal neurogenesis. Consequently, it has been suggested that a deficit in hippocampal neurogenesis is implicated in the pathophysiology of depression. To study a potential correlation between recovery and hippocampal cytogenesis, we established the chronic mild stress (CMS) rat model of depression. When rats are subjected to CMS, several depressive symptoms develop, including the major symptom anhedonia. Rats were exposed to stress for 2 weeks and subsequently to stress in combination with antidepressant treatment for 4 consecutive weeks. The behavioral deficit measured in anhedonic animals is a reduced intake of a sucrose solution. Prior to perfusion animals were injected with bromodeoxyuridine (BrdU), a marker of proliferating cells. Brains were sectioned horizontally and newborn cells positive for BrdU were counted in the dentate gyrus and tracked in a dorsoventral direction.CMS significantly decreased sucrose consumption and cytogenesis in the ventral part of the hippocampal formation. During exposure to the antidepressant escitalopram, given as intraperitoneally dosages of either 5 or 10 mg/kg/ day, animals distributed in a bimodal fashion into a group, which recovered (increase in sucrose consumption), and a subgroup, which refracted treatment (no increase in sucrose consumption). Chronic treatment with escitalopram reversed the CMS-induced decrease in cytogenesis in the dentate gyrus of the ventral hippocampal formation, but in recovered animals only. Our data show a correlation between recovery from anhedonia, as measured by cessation of behavioral deficits in the CMS model, and an increase in cytogenesis in the dentate gyrus of the ventral hippocampal formation.

“…Reduced body weight gain and enlarged adrenals are reliable indices for stress experience in rats (Muscat and Willner, 1992;Sapolsky et al, 2000). Because of the repeated social defeat, stressed rats gained less body weight than did the control rats after 2 (po0.05), 3 (po0.01), 4 (po0.01), and 5 (po0.01) weeks of social stress, as compared with controls ( Figure 2a).…”

Section: Changes Of Body and Adrenal Weights As An Indicator Of Stresmentioning

confidence: 93%

Chronic Social Stress Inhibits Cell Proliferation in the Adult Medial Prefrontal Cortex: Hemispheric Asymmetry and Reversal by Fluoxetine Treatment

Czéh

Müller-Keuker

Ryguła

et al. 2006

316

221

Profound neuroplastic changes have been demonstrated in various limbic structures after chronic stress exposure and antidepressant treatment in animal models of mood disorders. Here, we examined in rats the effect of chronic social stress and concomitant antidepressant treatment on cell proliferation in the medial prefrontal cortex (mPFC). We also examined possible hemispheric differences. Animals were subjected to 5 weeks of daily social defeat by an aggressive conspecific and received concomitant, daily, oral fluoxetine (10 mg/kg) during the last 4 weeks. Bromodeoxyuridine (BrdU) labeling and quantitative stereological techniques were used to evaluate the treatment effects on proliferation and survival of newborn cells in limbic structures such as the mPFC and the hippocampal dentate gyrus, in comparison with nonlimbic structures such as the primary motor cortex and the subventricular zone. Phenotypic analysis showed that neurogenesis dominated the dentate gyrus, whereas in the mPFC most newborn cells were glia, with smaller numbers of endothelial cells. Chronic stress significantly suppressed cytogenesis in the mPFC and neurogenesis in the dentate gyrus, but had minor effect in nonlimbic structures. Fluoxetine treatment counteracted the inhibitory effect of stress. Hemispheric comparison revealed that the rate of cytogenesis was significantly higher in the left mPFC of control animals, whereas stress inverted this asymmetry, yielding a significantly higher incidence of newborn cells in the right mPFC. Fluoxetine treatment abolished hemispheric asymmetry in both control and stressed animals. These pronounced changes in gliogenesis after chronic stress exposure may relate to the abnormalities of glial cell numbers reported in the frontolimbic areas of depressed patients.