A ΔFOSB mediated transcriptional response in the nucleus accumbens (NAc) is induced by chronic social stress in rodent and a 50% down-regulation of ΔFOSB has been also reported in the NAc of eight depressed subjects. To evaluate the role of ΔFOSB in the prefrontal cortex which is critically involved in negative cognitive bias associated with major depressive disorder (MDD) we have quantified the mRNA levels of ΔFOSB and of five of its major target genes in the Brodmann area 46 from 24 patients with MDD (11 with psychotic symptoms) and 12 controls.
Expression of the six genes has been quantified by a real-time quantitative PCR method: ΔFOSB, GRIA2 (encoding the GluR2 subunit of the AMPA receptor), SPARCL1 (encoding hevin), SG3 (encoding the secretogranin III), PCP4 (encoding the Purkinje cell protein 4), ATP6V0C (encoding a subunit of the lysosomal ATPase).
Expression of ΔFOSB and GRIA2 was significantly up-regulated (≈ 1.60) in the BA 46 of MDD patients. Overexpression of SCG3 and PCP4 was restricted to psychotic subjects. The mRNA levels of GRIA2, SCG3 and PCP4 were strongly correlated in the depressed group.
All the patients were treated by antidepressants and the number of subjects in each subgroup was rather small.
Induction of a ΔFOSB mediated transcriptional pattern in the prefrontal cortex is opposite to the down-regulation observed in the NAc. The major consequence might be a shift in the excitability of the glutamatergic synapses which depends on GluR2 (high in the NAc and low in the BA 46).
[Show abstract][Hide abstract] ABSTRACT: Exposure to stressful events can be differently perceived by individuals and can have persistent sequelae depending on the level of stress resilience or vulnerability of each person. The neural processes that underlie such clinically and socially important differences reside in the anatomical, functional, and molecular connectivity of the brain. Recent work has provided novel insight into some of the involved biological mechanisms that promises to help prevent and treat stress-related disorders. In this review, we focus on causal and mechanistic evidence implicating altered functions and connectivity of the neuroendocrine system, and of hippocampal, cortical, reward, and serotonergic circuits in the establishment and the maintenance of stress resilience and vulnerability. We also touch upon recent findings suggesting a role for epigenetic mechanisms and neurogenesis in these processes and briefly discuss promising avenues of future investigation.
[Show abstract][Hide abstract] ABSTRACT: In the present study, genomic binding sites of glucocorticoid receptors (GR) were identified in vivo in the rat hippocampus applying chromatin immunoprecipitation followed by next-generation sequencing. We identified 2470 significant GR-binding sites (GBS) and were able to confirm GR binding to a random selection of these GBS covering a wide range of P values. Analysis of the genomic distribution of the significant GBS revealed a high prevalence of intragenic GBS. Gene ontology clusters involved in neuronal plasticity and other essential neuronal processes were overrepresented among the genes harboring a GBS or located in the vicinity of a GBS. Male adrenalectomized rats were challenged with increasing doses of the GR agonist corticosterone (CORT) ranging from 3 to 3000 μg/kg, resulting in clear differences in the GR-binding profile to individual GBS. Two groups of GBS could be distinguished: a low-CORT group that displayed GR binding across the full range of CORT concentrations, and a second high-CORT group that displayed significant GR binding only after administering the highest concentration of CORT. All validated GBS, in both the low-CORT and high-CORT groups, displayed mineralocorticoid receptor binding, which remained relatively constant from 30 μg/kg CORT upward. Motif analysis revealed that almost all GBS contained a glucocorticoid response element resembling the consensus motif in literature. In addition, motifs corresponding with new potential GR-interacting proteins were identified, such as zinc finger and BTB domain containing 3 (Zbtb3) and CUP (CG11181 gene product from transcript CG11181-RB), which may be involved in GR-dependent transactivation and transrepression, respectively. In conclusion, our results highlight the existence of 2 populations of GBS in the rat hippocampal genome.
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The glutamatergic mechanism of antidepressant treatments is now in the center of research to overcome the limitations of monoamine-based approaches. There are several unresolved issues. For the action of the model compound, ketamine, NMDA-receptor block, AMPA-receptor activation and BDNF release appear to be involved in a mechanism, which leads to synaptic sprouting and strengthened synaptic connections. The link to the pathophysiology of depression is not clear. An overlooked connection is the role of magnesium, which acts as physiological NMDA-receptor antagonist: 1. There is overlap between the actions of ketamine with that of high doses of magnesium in animal models, finally leading to synaptic sprouting. 2. Magnesium and ketamine lead to synaptic strengthening, as measured by an increase in slow wave sleep in humans. 3. Pathophysiological mechanisms, which have been identified as risk factors for depression, lead to a reduction of (intracellular) magnesium. These are neuroendocrine changes (increased cortisol and aldosterone) and diabetes mellitus as well as Mg(2+) deficiency. 4. Patients with therapy refractory depression appear to have lower CNS Mg(2+) levels in comparison to health controls. 5. Experimental Mg(2+) depletion leads to depression- and anxiety like behavior in animal models. 6. Ketamine, directly or indirectly via non-NMDA glutamate receptor activation, acts to increase brain Mg(2+) levels. Similar effects have been observed with other classes of antidepressants. 7. Depressed patients with low Mg(2+) levels tend to be therapy refractory. Accordingly, administration of Mg(2+) either alone or in combination with standard antidepressants acts synergistically on depression like behavior in animal models.
On the basis of the potential pathophysiological role of Mg(2+)-regulation, it may be possible to predict the action of ketamine and of related compounds based on Mg(2+) levels. Furthermore, screening for compounds to increase neuronal Mg(2+) concentration could be a promising instrument to identify new classes of antidepressants. Overall, any discussion of the glutamatergic system in affective disorders should consider the role of Mg(2+).
Journal of Psychiatric Research 03/2013; 47(7). DOI:10.1016/j.jpsychires.2013.02.015 · 3.96 Impact Factor
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