Subfield‐specific effects of chronic mild unpredictable stress on hippocampal astrocytes

Abstract

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 S100β 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.

Hippocampal astroglial hypertrophy in mice subjected to early life maternal deprivation

“…The hypertrophy seen in the hippocampal astrocytes of maternally separated mice strongly hints at a possible reactive phenotype. Although astrocytes show a high degree of structural plasticity (Schiweck et al, 2018;Sethi et al, 2021;Virmani et al, 2021), the extent of hypertrophy seen in this study is most often associated with neurological disorders or normal ageing (Lindsey et al, 1979;Wang et al, 2006;Rodríguez et al, 2014;Joe et al, 2018;Verkhratsky et al, 2019;Bondi et al, 2021). In particular, hypertrophic astrocytes in the hippocampus appear from about 14 months and beyond in ageing rodents (Rodríguez et al, 2014;Matias et al, 2019;Bondi et al, 2021).…”

“…Immunofluorescence and imaging: Immunofluorescence was performed as described previously (Virmani et al, 2021). In brief, sections were washed thrice in 0.1M PB and followed by a 1-2 hour incubation with a blocking solution (1% normal donkey serum, 3% bovine serum albumin, 0.3% Triton X-100, prepared in 0.1 M PB) at room temperature.…”

“…Astrocytic structure is highly dynamic and astrocytes show plasticity in response to physiological and pathological stimuli (Schiweck et al, 2018). Interestingly, hippocampal astrocytes exhibit structural plasticity following chronic stress and chronic antidepressant therapy (Sethi et al, 2021;Virmani et al, 2021). Astrocytes have also been shown to undergo alterations in maternally separated (MS) animals, although the results have been inconsistent.…”

Special issue editorial: Glial plasticity in health and disease

“…In particular, this paper presents the novel development of astrocytic phagocytosis in the physiological and pathological brain. Finally, Garima Virmani, Priyal D'almeida, Arnab Nandi, and Swananda Marathe from India (Virmani et al, 2021) present data demonstrating that chronic mild unpredictable stress affects hippocampal astrocytic morphology in a nonuniform way. Exposure to chronic stress diminishes astrocytic complexity in the dentate gyrus but does not affect astroglial morphology in the CA1 regions and in the hilus.…”

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

“…The FST protocol was adapted from previous studies ( Castagné et al, 2011 ; Jaggar et al, 2017 ); 6-min-long FST protocols have also been used, with the first 2 min removed from analysis ( Can et al, 2012a ; Kara et al, 2018 ). The choice of the method in this study was based on a protocol standardized earlier in a similar chronic stress paradigm ( Virmani et al, 2021 ). Every effort was made to minimize the effects of reflected light from the water surface.…”