Gene expression profiling as functional readout of rodent models for psychiatric disorders

Animal models of depression: pros and cons

Animal models of depression are certainly needed but the question in the title has been raised owing to the controversies in the interpretation of the readout in a number of tests, to the perceived lack of progress in the development of novel treatments and to the expressed doubts in whether animal models can offer anything to make a true breakthrough in understanding the neurobiology of depression and producing novel drugs against depression. Herewith, it is argued that if anything is wrong with animal models, including those for depression, it is not about the principle of modelling complex human disorder in animals but in the way the tests are selected, conducted and interpreted. Further progress in the study of depression and in developing new treatments, will be supported by animal models of depression if these were more critically targeted to drug screening vs. studies of underlying neurobiology, clearly stratified to vulnerability and pathogenetic models, focused on well-defined endophenotypes and validated for each setting while bearing the existing limits to validation in mind. Animal models of depression need not to rely merely on behavioural readouts but increasingly incorporate neurobiological measures as the understanding of depression as human brain disorder advances. Further developments would be fostered by cross-fertilizinga translational approach that is bidirectional, research on humans making more use of neurobiological findings in animals.

Alterations in splenic function and gene expression in mice with depressive-like behavior induced by exposure to corticosterone

Depressed patients present with increased cortisol levels and attenuated immune responses. However, little is known about the association between depression and the spleen, as this is the largest peripheral immune organ. In this study, we examined alterations in splenic function and gene expression in mice with depressive-like behavior, well as the expression of certain proteins in related pathways. A mouse model of depression was established with the use of corticosterone. Splenic function and histopathology were assessed using Wright and H&E staining. The Agilent Whole Mouse Genome Oligo Microarray containing >41,174 transcript probes was used to measure the levels of gene-expression in the spleens from control and model mice, and the levels of certain proteins associated with depression were measured by western blot analysis in the brain and spleen separately. We found that splenic function and immunity in the mice with depressive-like behavior were markedly impaired. A total of 53 genes exhibited a differential response in the mice with depressive-like behavior, 11 of which were more notable, including collagen, type VI, α5 (Col6a5), immunoglobulin superfamily, member 11 (Igsf11), D site albumin promoter binding protein (Dbp), tachykinin 2 (Tac2) and γ-aminobutyric acid B receptor 2 (Gabbr2). Pathway analysis revealed that the amino acid biosynthesis and the clock gene pathways were more meaningful among these genes. The levels of GABBR2, DBP and substance P (SP; encoded by the Tac2 gene) related proteins in the brain were markedly downregulated, and similar results were observed in the spleen. The anti-depressant, fluoxetine, reversed the changes in the levels of these proteins. The findings of our study regarding changes occurring in the spleen during depression may indirectly elucidate and shed light into the pathogenesis of depression and depressive-like behavior.

Sex-Specific Effects of Prenatal Stress on Bdnf Expression in Response to an Acute Challenge in Rats: a Role for Gadd45β

Exposure to early adversities represents a major risk factor for psychiatric disorders. We have previously shown that exposure to prenatal stress (PNS) in rats alters the developmental expression of brain-derived neurotrophic factor (Bdnf) with a specific temporal profile. However, exposure to early-life stress is known to alter the ability to cope with challenging events later in life, which may contribute to the enhanced vulnerability to stress-related disorders. Since Bdnf is also an important player for activity-dependent plasticity, we investigated whether the exposure to PNS in rats could alter Bdnf responsiveness to an acute challenge at adulthood. We found that exposure to PNS produces significant changes in Bdnf responsiveness with brain region- and gender-specific selectivity. Indeed, exposure to an acute stress upregulates Bdnf expression in the prefrontal cortex, but not in the hippocampus, of control animals. Moreover, such modulatory activity is selectively impaired in PNS female rats, an effect that was associated with changes in the modulation of the DNA demethylase Gadd45β. Our results suggest that exposure to PNS may reprogram gene transcription through epigenetic mechanisms reducing the ability to cope under adverse conditions, a trait that is disrupted in psychiatric diseases.

Ghrelin effects expression of several genes associated with depression-like behavior

Ghrelin (Ghr) is an orexigenic peptide that is being investigated for its potential role in development of anxiety-like behavior and modulation of depressive-like symptoms induced by bilateral olfactory bulbectomy (OB) in rodents. Olfactory bulbectomy is an animal model useful to study of depression and Ghr could be an alternative therapeutic tool in depression therapy. We studied the effects of intracerebroventricular (i.c.v.) Ghr administration on the expression of hypothalamic genes related to depression and mood (delta opioid receptor (DOR), mu opioid receptor (MOR) and kappa opioid receptor (KOR), lutropin-choriogonadotropic hormone receptor (LHCGR), serotonin transporter (SERT), interleukin 1 beta (IL-1b), vasopressin (AVP) and corticotrophin releasing hormone (CRH)) in OB animals, as well as changes in plasma levels of AVP, CRH and adenocorticotropic hormone (ACTH). We found that acute Ghr 0.3 nmol/μl administration increases gene expression of DOR, SERT and LHCGR in OB mice and decreased expression of IL-1b, suggesting that these genes could be involved in the antidepressant-like effects of Ghr. In addition, OB animals exhibit high AVP gene expression and elevated plasma concentrations of AVP and ACTH and acute Ghr 0.3 nmol/μl administration reduces AVP gene expression and the concentration of these hormones, suggesting that peptide-effects on depressive-like behavior could be mediated at least in part via AVP. In conclusion, this study provides new evidence about genes, receptors and hormones involved in the antidepressant mechanism/s induced by Ghr in OB animals.