DBscorer: An Open-Source Software for Automated Accurate Analysis of Rodent Behavior in Forced Swim Test and Tail Suspension Test.

Forced swim test (FST) and tail suspension test (TST) are commonly used behavioral tests for screening antidepressant drugs with a high predictive validity. These tests have also proved useful to assess the non-motor symptoms in the animal models of movement disorders such as Parkinson's disease and Huntington's disease. Manual analysis of FST and TST is a time-consuming exercise and has large observer-to-observer variability. Automation of behavioral analysis alleviates these concerns, but there are no easy-to-use open-source tools for such analysis. Here, we describe the development of Depression Behavior Scorer (DBscorer), an open-source program installable on Windows, with an intuitive graphical user interface (GUI), that helps in accurate quantification of immobility behavior in FST and TST from video analysis. Several calibration options allow customization of various parameters to suit the experimental requirements. Apart from the readout of time spent immobile, DBscorer also provides additional data and graphics of immobility/mobility states across time revealing the evolution of behavioral despair over the duration of the test and allows the analysis of additional parameters. Such comprehensive analysis allows a more nuanced understanding of the expression of behavioral despair in FST and TST. We believe that DBscorer would make analysis of behavior in FST and TST unbiased, automated and rapid, and hence prove to be helpful to the wider neuroscience community.

Automated morphometric analysis with SMorph software reveals plasticity induced by antidepressant therapy in hippocampal astrocytes.

Nervous system development and plasticity involve changes in cellular morphology, making morphological analysis a valuable exercise in the study of nervous system development, function and disease. Morphological analysis is a time-consuming exercise requiring meticulous manual tracing of cellular contours and extensions. We have developed a software tool, called SMorph, to rapidly analyze the morphology of cells of the nervous system. SMorph performs completely automated Sholl analysis. It extracts 23 morphometric features based on cell images and Sholl analysis parameters, followed by principal component analysis (PCA). SMorph was tested on neurons, astrocytes and microglia and reveals subtle changes in cell morphology. Using SMorph, we found that chronic 21-day treatment with the antidepressant desipramine results in a significant structural remodeling in hippocampal astrocytes in mice. Given the proposed involvement of astroglial structural changes and atrophy in major depression in humans, our results reveal a novel kind of structural plasticity induced by chronic antidepressant administration.

Subfield-specific effects of chronic mild unpredictable stress on hippocampal astrocytes.

Major depressive disorder (MDD) is a debilitating neuropsychiatric illness affecting over 20% of the population worldwide. Despite its prevalence, our understanding of its pathophysiology is severely limited, thus hampering the development of novel therapeutic strategies. Recent advances have clearly established astrocytes as major players in the pathophysiology, and plausibly pathogenesis, of major depression. In particular, astrocyte density in the hippocampus is severely diminished in MDD patients and correlates strongly with the disease outcome. Moreover, astrocyte densities from different subfields of the hippocampus show varying trends in terms of their correlation to the disease outcome. Given the central role that hippocampus plays in the pathophysiology of depression and in the action of antidepressant drugs, changes in hippocampal astrocyte density and physiology may have a significant effect on behavioral symptoms of MDD. In this study, we used chronic mild unpredictable stress (CMUS) in mice, which induces a depressive-like state, and examined its effects on astrocytes from different subfields of the hippocampus. We used SOX9 and S100ß immunostaining to estimate the number of astrocytes per square millimeter from various hippocampal subfields. Furthermore, using confocal images of fluorescently labeled glial fibrillary acidic protein (GFAP)-immunopositive hippocampal astrocytes, we quantified various morphology-related parameters and performed Sholl analysis. We found that CMUS exerts differential effects on astrocyte cell numbers, ramification, cell radius, surface area, and process width of hippocampal astrocytes from different hippocampal subfields. Taken together, our study reveals that chronic stress does not uniformly affect all hippocampal astrocytes; but exerts its effects differentially on different astrocytic subpopulations within the hippocampus.

SRF Is Required for Maintenance of Astrocytes in Non-Reactive State in the Mammalian Brain.

Astrocytes play several critical roles in the normal functioning of the mammalian brain, including ion homeostasis, synapse formation, and synaptic plasticity. Following injury and infection or in the setting of neurodegeneration, astrocytes become hypertrophic and reactive, a process termed astrogliosis. Although acute reactive gliosis is beneficial in limiting further tissue damage, chronic gliosis becomes detrimental for neuronal recovery and regeneration. Several extracellular factors have been identified that generate reactive astrocytes; however, very little is known about the cell-autonomous transcriptional mechanisms that regulate the maintenance of astrocytes in the normal non-reactive state. Here, we show that conditional deletion of the stimulus-dependent transcription factor, serum response factor (SRF) in astrocytes (SrfGFAPCKO) results in astrogliosis marked by hypertrophic morphology and increased expression of GFAP, vimentin, and nestin. These reactive astrocytes were not restricted to any specific brain region and were seen in both white and gray matter in the entire brain. This astrogliosis persisted throughout adulthood concomitant with microglial activation. Importantly, the Srf mutant mouse brain did not exhibit any cell death or blood brain barrier (BBB) deficits suggesting that apoptosis and leaky BBB are not the causes for the reactive phenotype. The mutant astrocytes expressed more A2 reactive astrocyte marker genes and the SrfGFAPCKO mice exhibited normal neuronal numbers indicating that SRF-deficient gliosis astrocytes are not neurotoxic. Together, our findings suggest that SRF plays a critical role in astrocytes to maintain them in a non-reactive state.

Effects of Monoamines and Antidepressants on Astrocyte Physiology: Implications for Monoamine Hypothesis of Depression.

Major depressive disorder (MDD) is one of the most common neuropsychiatric disorders affecting over one-fifth of the population worldwide. Owing to our limited understanding of the pathophysiology of MDD, the quest for finding novel antidepressant drug targets is severely impeded. Monoamine hypothesis of MDD provides a robust theoretical framework, forming the core of a large jigsaw puzzle, around which we must look for the vital missing pieces. Growing evidence suggests that the glial loss observed in key regions of the limbic system in depressed patients, at least partly, accounts for the structural and cognitive manifestations of MDD. Studies in animal models have subsequently hinted at the possibility that the glial atrophy may play a causative role in the precipitation of depressive symptoms. Antidepressants as well as monoamine neurotransmitters exert profound effects on the gene expression and metabolism in astrocytes. This raises an intriguing possibility that the astrocytes may play a central role alongside neurons in the behavioral effects of antidepressant drugs. In this article, we discuss the gene expression and metabolic changes brought about by antidepressants in astrocytes, which could be of relevance to synaptic plasticity and behavioral effects of antidepressant treatments.