Pro-apoptotic Action of Corticosterone in Hippocampal Organotypic Cultures

Neurotox Res (2016) 30:225–238 DOI 10.1007/s12640-016-9630-8 ORIGINAL ARTICLE Pro-apoptotic Action of Corticosterone in Hippocampal Organotypic Cultures Anna Kurek1 • Mateusz Kucharczyk1,3 • Jan Detka1 • Joanna Ślusarczyk1 • Ewa Trojan1 • Katarzyna Głombik1 • Bartosz Bojarski2 • Agnieszka Ludwikowska1 • Władysław Lasoń1 • Bogusława Budziszewska1 Received: 21 January 2016 / Revised: 6 May 2016 / Accepted: 7 May 2016 / Published online: 17 May 2016 Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Elevated levels of glucocorticoids exert neurotoxic effects, and the hippocampus is particularly sensitive to the effects of glucocorticoids. Because some data have indicated that an increased action of glucocorticoids in the perinatal period enhances the susceptibility of brain tissue to adverse substances later in life, the main purpose of the present study was to compare necrotic/apoptotic corticosterone action in hippocampal organotypic cultures obtained from control animals with the effect of this steroid in tissue from prenatally stressed rats. Because the adverse effects of glucocorticoid action on nerve cell viability appear to result mainly from an increase in the intensity of the effects of glutamate and changes in growth factor and pro-inflammatory cytokine synthesis, the involvement of these factors in corticosterone action were also determined. In stress-like concentration (1 lM), corticosterone, when added to hippocampal cultures for 1 and 3 days, alone or jointly with glutamate, did not induce necrosis. In contrast, in 3-day cultures, corticosterone (1 lM) increased caspase-3 activity and the mRNA expression of the pro-apoptotic Bax. Electronic supplementary material The online version of this article (doi:10.1007/s12640-016-9630-8) contains supplementary material, which is available to authorized users. & Bogusława Budziszewska 1 Department of Experimental Neuroendocrinology, Institute of Pharmacology, Polish Academy of Sciences, 12 Sme˛tna Street, 31-343 Kraków, Poland 2 Department of Veterinary Science, Faculty of Animal Science, University of Agriculture, 24/28 Mickiewicza Street, 30-059 Kraków, Poland 3 Department of Neuroscience, Physiology and Pharmacology, University College London, Gower St, London WC1E 6BT, UK Moreover, corticosterone’s effect on caspase-3 activity was stronger in hippocampal cultures from prenatally stressed compared to control rats. Additionally, 24 h of exposure to corticosterone and glutamate, when applied separately and together, increased Bdnf, Ngf, and Tnf-a expression. In contrast, after 72 h, a strong decrease in the expression of both growth factors was observed, while the expression of TNF-a remained high. The present study showed that in stress-like concentrations, corticosterone exerted proapoptotic but not necrotic effects in hippocampal organotypic cultures. Prenatal stress increased the pro-apoptotic effects of corticosterone. Increased synthesis of the proinflammatory cytokine TNF-a may be connected with the adverse effects of corticosterone on brain cell viability. Keywords Corticosterone  Glutamate  Apoptosis  Hippocampus  Organotypic cultures Introduction Glucocorticoids easily cross the blood–brain barrier and bind to intracellular mineralocorticoid (MR) and glucocorticoid (GR) receptors in neuronal and glial cells. Glucocorticoids are essential for the maintenance of homeostasis and adaptations to stress; however, their longterm, excessive release leads to damage of different brain structures, particularly the hippocampus. The hippocampus is one of the most sensitive regions of the brain to neurotoxic factors. This structure plays a significant role in learning and memory processes (Eichenbaum et al. 1992; De Kloet et al. 1999; Hui et al. 2004); therefore, its injury disturbs vital functions of the body. It is well described that prolonged stress or long-term glucocorticoid treatment causes neuronal loss in the hippocampus (especially in the 123 226 CA3 region) in rats and primates (McEwen 1999; Sapolsky et al. 1985, 1990), evokes reorganization of dendrites in hippocampal area CA3, reduces branch density and the number of synapses, and inhibits neurogenesis (Duman 2002; Magarinos et al. 1999; Sousa et al. 2000). However, the neurotoxic mechanism of glucocorticoid action is poorly understood. It is known that increased glucocorticoid concentrations can enhance synaptic glutamate concentrations, affect the synthesis and action of proinflammatory cytokines and attenuate the synthesis of brain-derived neurotrophic factor (BDNF). All of these changes may be responsible for nerve cell damage and also seem to be involved in the pathogenesis of affective disorders. It is known that the effects of glucocorticoids depend not only on their concentration and duration of action but also on the period of life in which an organism is exposed to them. In adult animals, these hormones usually evoke short-lasting changes, while glucocorticoid exposure in the perinatal period permanently changes the expression of some genes and, as a consequence, causes long-lasting disturbances in the levels of neurotransmitters, their receptors, hypothalamic–pituitary–adrenal (HPA) axis activity, and GR regulatory factors (Matthews 2000; Szymańska et al. 2009). Moreover, glucocorticoids acting in the perinatal period can increase tissue susceptibility to the adverse effects of lipopolysaccharide, stress, and glutamate in adulthood (Diz-Chaves et al. 2013; Kohman et al. 2008; Szcze˛sny et al. 2014). Furthermore, prenatal stress has been shown to weaken neurogenesis-related processes in the dentate gyrus of the hippocampus and to lower cell survival in young and adult animals (Lemaire et al. 2006). We previously showed that prenatal stress enhanced the effect of immobilization stress or peripheral glucose administration on brain glucose, glycogen, corticosterone, and glucose transporter concentrations in later life (Detka et al. 2014, 2015). The existing data on the participation of glucocorticoids in neurotoxicity and the pathogenesis of depression indicate that an increase in the intensity of glutamate action, most likely through inhibition of its uptake by astrocytes and elevation of its extracellular level, is the most substantial mechanism underlying the effects of glucocorticoids. This hypothesis is supported by data showing that increased glucocorticoid or glutamate levels induce similar changes in the apical dendrites of pyramidal cells in hippocampal area CA3 and that the administration of an antagonist of excitatory amino acid receptors prevented these changes (Magariños and McEwen 1995). However, in contrast to in vivo studies, the majority of in vitro experiments have not produced unequivocal results and documented the neurotoxic potential of glucocorticoids only when they were used at very high concentrations. 123 Neurotox Res (2016) 30:225–238 Although the studie (...truncated)