Changes in the Orexin System in Rats Exhibiting Learned Helplessness Behaviors

Orexin-A (OX-A) and orexin-B (OX-B) are neuropeptides produced in the hypothalamus. Preclinical and clinical studies suggest that depression and anxiety are associated with the orexin system. In the current study, we used the learned helplessness (LH) animal model of depression to identify rats displaying LH behaviors (LH rats) and those that did not (No-LH rats). We compared the number of orexin-containing neurons in the hypothalamus of LH, No-LH, and control rats. Orexin peptides, orexin receptor 1 (OXR1) and 2 (OXR2) in brain areas involved in major depression and serum OX-A and corticosterone (CORT) concentrations were quantified and compared between rat groups. We found that LH and No-LH rats displayed higher serum OX-A concentrations compared with control rats. Comparison between LH and No-LH rats revealed that No-LH rats had significantly higher OX-A levels in the brain, more OX-A neurons, and more OX-A neuron activation. LH rats had more OX-B neurons and more OX-B neuron activation. Orexin peptides and receptors in the brain areas involved in major depression exhibited different patterns in LH and NoLH rats. Our findings revealed that activation of OX-A neurons could promote resilient behaviors under stressful situations and OX-A and OX-B neuropeptides exhibit dissimilar functions in LH behaviors.

Establishment of an Animal Model of Depression: The Serotonin Transporter Knockout Rat

<p>Major depressive disorder (MDD) is a serious and debilitating psychiatric illness found of increasing prevalence. Despite this, our current first line treatments have been shown to lack efficacy and possess a high non-response rate. Most new pharmacological developments have not shown efficacy in humans, likely due to our current models being outdated. This thesis attempts to use a range of novel approaches, integrating behavioural, physiological, and biological methods to provide support for the use of the serotonin transporter knockout (SERT-KO) rat to model components of MDD in humans. Social anhedonia is assessed through conditioned place preference and play behaviour analysis, demonstrating significantly reduced reward sensitivity in SERT-/- animals. Comorbid anxiety is assessed using a modified successive alleys test, whereby SERT-/- animals demonstrate increased anxiety behaviour, which persist over the course of the experiment. The assessment of heart rate variability, a physiological correlate of MDD was impacted by time constraints, however suggests a likely reduction to be present in the SERT-/- animals. Finally, neurogenesis was found to be significantly increased in SERT-/- animals during early development (PND7), demonstrating neurodevelopmental alterations associated with reduced SERT expression. These data demonstrate that the SERT knockout rat possesses many deficits associated with MDD, thus being a likely candidate for novel pharmacological development. A final pilot experiment was conducted using MALDI-TOF to provide a method of examining potentially thousands of compounds in brain and cardiac tissue with high spatial definition. Applications and implication of this research are discussed in detail with suggestions for future studies being presented.</p>

Establishment of an Animal Model of Depression: The Serotonin Transporter Knockout Rat

<p>Major depressive disorder (MDD) is a serious and debilitating psychiatric illness found of increasing prevalence. Despite this, our current first line treatments have been shown to lack efficacy and possess a high non-response rate. Most new pharmacological developments have not shown efficacy in humans, likely due to our current models being outdated. This thesis attempts to use a range of novel approaches, integrating behavioural, physiological, and biological methods to provide support for the use of the serotonin transporter knockout (SERT-KO) rat to model components of MDD in humans. Social anhedonia is assessed through conditioned place preference and play behaviour analysis, demonstrating significantly reduced reward sensitivity in SERT-/- animals. Comorbid anxiety is assessed using a modified successive alleys test, whereby SERT-/- animals demonstrate increased anxiety behaviour, which persist over the course of the experiment. The assessment of heart rate variability, a physiological correlate of MDD was impacted by time constraints, however suggests a likely reduction to be present in the SERT-/- animals. Finally, neurogenesis was found to be significantly increased in SERT-/- animals during early development (PND7), demonstrating neurodevelopmental alterations associated with reduced SERT expression. These data demonstrate that the SERT knockout rat possesses many deficits associated with MDD, thus being a likely candidate for novel pharmacological development. A final pilot experiment was conducted using MALDI-TOF to provide a method of examining potentially thousands of compounds in brain and cardiac tissue with high spatial definition. Applications and implication of this research are discussed in detail with suggestions for future studies being presented.</p>

Neurogenesis-dependent antidepressant-like activity of Hericium erinaceus in an animal model of depression

Background Depression is a severe neuropsychiatric disorder that affects more than 264 million people worldwide. The efficacy of conventional antidepressants are barely adequate and many have side effects. Hericium erinaceus (HE) is a medicinal mushroom that has been reported to have therapeutic potential for treating depression. Methods Animals subjected to chronic restraint stress were given 4 weeks HE treatment. Animals were then screened for anxiety and depressive-like behaviours. Gene and protein assays, as well as histological analysis were performed to probe the role of neurogenesis in mediating the therapeutic effect of HE. Temozolomide was administered to validate the neurogenesis-dependent mechanism of HE. Results The results showed that 4 weeks of HE treatment ameliorated depressive-like behaviours in mice subjected to 14 days of restraint stress. Further molecular assays demonstrated the 4-week HE treatment elevated the expression of several neurogenesis-related genes and proteins, including doublecortin, nestin, synaptophysin, brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB), phosphorylated extracellular signal-regulated kinase, and phosphorylated cAMP response element-binding protein (pCREB). Increased bromodeoxyuridine-positive cells were also observed in the dentate gyrus of the hippocampus, indicating enhanced neurogenesis. Neurogenesis blocker temozolomide completely abolished the antidepressant-like effects of HE, confirming a neurogenesis-dependent mechanism. Moreover, HE induced anti-neuroinflammatory effects through reducing astrocyte activation in the hippocampus, which was also abolished with temozolomide administration. Conclusion HE exerts antidepressant effects by promoting neurogenesis and reducing neuroinflammation through enhancing the BDNF-TrkB-CREB signalling pathway.

Galanin(1-15) Potentiates the Antidepressant-like Effects Induced by Escitalopram in a Rat Model of Depression

Selective 5-HT reuptake inhibitor antidepressants (SSRIs) are the first choice in major depressive disorder (MDD), but 50% of affected patients do not show improvement. Galanin(1-15) [GAL(1-15)] enhanced Fluoxetine antidepressant-like effects in an animal model of depression, the olfactory bulbectomy (OBX); however, further detailed analysis of GAL(1-15) effects as augmentation treatment in OBX rats are needed. In OBX rats, we analysed the effect of GAL(1–15) on Escitalopram (ESC)-mediated responses in behavioural tests related to despair. We studied whether GAL(1–15) effects involved 5-HT1AR using an in vivo model siRNA 5-HT1A knockdown rats. Moreover, we analysed by immunohistochemistry the expression of the immediate-early gene c-Fos (c-Fos IR) after the administration of GAL(1-15)+ESC in OBX rats in several nuclei involved in MDD. GAL(1-15) enhances the antidepressant-like effects of ESC, and the GALR2 antagonist M871 blocked GAL(1-15) mediated actions. The downregulation of 5-HT1AR by siRNA was sufficient to block GAL(1-15) effects. Our immunohistochemistry and principal component analysis (PCA) analysis suggest that two functional networks are involved in these effects; one includes the lateral (LHb) and medial (mHb) habenula, dorsal raphe (DR) and ventral tegmental area (VTA), and the other consists of the dentate gyrus (DG), and prefrontal cortex (PFC). The results open up the possibility of using GAL(1-15) in combination with SSRIs as a novel strategy for treating MDD.

Tianeptine modulates synaptic vesicle dynamics and favors synaptic mitochondria processes in socially isolated rats

Deregulation of synaptic function and neurotransmission has been linked with the development of major depression disorder (MDD). Tianeptine (Tian) has been used as antidepressant with anxiolytic properties and recently as a nootropic to improve cognitive performance, but its mechanism of action is unknown. We conducted a proteomic study on the hippocampal synaptosomal fractions of adult male Wistar rats exposed to chronic social isolation (CSIS, 6 weeks), an animal model of depression and after chronic Tian treatment in controls (nootropic effect) and CSIS-exposed rats (lasting 3 weeks of 6-week CSIS) (therapeutic effect). Increased expression of Syn1 and Camk2-related neurotransmission, vesicle transport and energy processes in Tian-treated controls were found. CSIS led to upregulation of proteins associated with actin cytoskeleton, signaling transduction and glucose metabolism. In CSIS rats, Tian up-regulated proteins involved in mitochondrial energy production, mitochondrial transport and dynamics, antioxidative defense and glutamate clearance, while attenuating the CSIS-increased glycolytic pathway and cytoskeleton organization proteins expression and decreased the expression of proteins involved in V-ATPase and vesicle endocytosis. Our overall findings revealed that synaptic vesicle dynamics, specifically exocytosis, and mitochondria-related energy processes might be key biological pathways modulated by the effective nootropic and antidepressant treatment with Tian and be a potential target for therapeutic efficacy of the stress-related mood disorders.