Search

Disturbances of circadian rhythms have been suggested to be a causal factor in the development of major depressive disorder. However, the mechanisms underlying the association between circadian rhythm abnormalities and mood disorders are still unknown. In the current study the association between diurnal pattern of key phase markers (melatonin, corticosterone, and core body temperature) and anhedonic-like behavior was investigated using the highly validated rat chronic mild stress (CMS) model of depression. Phase marker measurements were done after 3.5 weeks of CMS in 48 control rats and 48 anhedonic-like rats at 6 time points within 24 h. The results showed that anhedonic-like behavior associates with changes in all three phase markers: an increased dark phase melatonin secretion, an additional peak in corticosterone level in the beginning of the light phase, and hypothermia in the dark phase. The result adds to the validity of the CMS model in general and in particular to be adequate as a model for studying the chronobiology of depressive disorder. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the present study was to identify potential biomarkers for depression in the search for novel disease targets and treatment regimens. Furthermore, the study includes a search for biomarkers involved in treatment resistance and stress resilience in order to investigate mechanisms underlying antidepressant drug refraction and stress-coping strategies. Depression-related transcriptomic changes in gene expression profiles were investigated in laser-captured microdissected (LCM) rat hippocampal granular cell layers (GCL) using the chronic mild stress (CMS) rat model of depression and chronic administration of two selective serotonin reuptake inhibitors (SSRIs), escitalopram and sertraline. CMS rats were segregated into diverging groups according to behavioral readouts, and under stringent constraints, the associated differential gene regulations were analyzed. Accordingly, we identified four genes associated with recovery, two genes implicated in treatment resistance, and three genes involved in stress resilience. The identified genes associated with mechanisms of cellular plasticity, including signal transduction, cell proliferation, cell differentiation, and synaptic release. Hierarchical clustering analysis confirmed the subgroup segregation pattern in the CMS model. Thus antidepressant treatment refractors cluster with anhedonic-like rats, and, interestingly, stress-resilient rats cluster with rats undergoing antidepressant-mediated recovery from anhedonia, suggesting antidepressant mechanisms of action to emulate endogenous stress-coping strategies. [Copyright &y& Elsevier]

Abstract: Several findings suggest a functional and anatomical differentiation along the dorso–ventral axis of the hippocampus. Lesion studies in rats have indicated that the dorsal hippocampus preferentially plays a role in spatial learning and memory, while the ventral hippocampus is involved in anxiety-related behaviors. Based on such findings our aim was to investigate the molecular differentiation along the dorso–ventral axis of the hippocampal granular cell layer of the rat dentate gyrus. Homogeneous isolation of this specific area was performed by laser-capture microdissection and Illumina microarray chips were used to identify genes differentially expressed in dorsal and ventral granular cell layer, respectively. Selected genes were confirmed by quantitative polymerase chain reaction analyses. From the total amount of 22518 probes 229 genes were found to be differentially expressed between dorsal and ventral granular cell layer with a false discovery rate below 5% and with a relative change in gene expression level of 20% or more. From this pool of genes 45 genes were more than two-fold regulated, 13 genes being dorsally enriched and 32 genes being ventrally enriched. Moreover, cluster analysis based on all genes represented on the microarray chip showed a clear differentiation between dorsal and ventral subgroups. Our findings demonstrate a dorso–ventral differentiation in gene expression even at the subregional level of the rat hippocampus, more specifically in the granular cell layer, substantiating the existence of functional heterogeneity along the dorso–ventral axis of the hippocampus. [Copyright &y& Elsevier]

Abstract: We used the validated chronic mild stress (CMS) paradigm to induce anhedonia, a core symptom of major depression, in rats. Thirty percent of animals exposed to CMS are resistant to the development of anhedonia, whereas the remaining are responsive, CMS resilient and CMS sensitive, respectively. We used in situ hybridization to elucidate the molecular mechanisms, which may be involved in the development of anhedonia during CMS. In the CA3 of the ventral hippocampus, we found upregulation of brain-derived neurotrophic factor (BDNF) mRNA in the CMS resilient group indicating protective role of BDNF in stress. Moreover, in the CA3 we found downregulation of vascular endothelial growth factor (VEGF) mRNA in the CMS sensitive group. Downregulation of VEGF suggests impaired hippocampal function, caused by loss of trophic factor neuroprotective support, as part of a previously uncharacterized mechanism for development of anhedonia. CMS induced anhedonia was not related to mRNA expression differences of the dopamine receptors D1 and D2, enkephalin, dynorphin, the NMDA receptor subtype NR2B in the ventral striatum, BDNF expression in the dentate gyrus, nor corticotrophin releasing hormone (CRH) and arginine vasopressin (AVP) in the paraventricular nucleus of the hypothalamus. In particular, HPA axis seems to be activated in the CMS resilient group suggesting other pathways protecting against stress sensitivity. We applied the restraint stress procedure to compare effects of a faster and simpler form of stress to CMS and found the latter to be more valid as rats probably easier adapt to restraint stress. Finally, we used the conditioned place preference model to demonstrate a clear tendency towards a distinct morphine induced behavioral difference between CMS resilient and CMS sensitive animals. [Copyright &y& Elsevier]