Quantitative Changes in Hippocampal Microvasculature of Chronically Stressed Rats: No Effect of Fluoxetine Treatment Boldizsa ´r Cze ´h, 1,2 * Nashat Abumaria, 1,2 Rafal Rygula, 1,2 and Eberhard Fuchs 1,2,3 ABSTRACT: Exposure to chronic stress alters the number and morphol- ogy of neurons and glia in the hippocampal formation; however, little is known about possible changes in vasculature. Here, we examined the effect of chronic social defeat stress on hippocampal vascular supply in rats. Recent reports document that antidepressant treatment can influence angiogenesis in the hippocampus; therefore, we also studied the effect of antidepressant drug treatment on hippocampal capillarization. Animals were subjected to 5 weeks of daily social defeat by an aggressive conspe- cific and received concomitant, daily, oral fluoxetine (10 mg/kg) treatment during the last 4 weeks. Rat endothelial cell antigen-1 (RECA-1)-labeling of capillaries and quantitative stereological techniques were used to evaluate the treatment effects on capillary number. Special attention was paid to analysis of the vascular supply of the subgranular zone, which is regarded as an important component of the neurogenic niche for adult hippocampal neurogenesis. Chronic stress significantly decreased the number of micro- vessels by 30% in all hippocampal subregions, whereas fluoxetine treat- ment had no influence on capillary number. Furthermore, chronic stress decreased the capillarization of the subgranular zone to a similar extent, indicating that chronic stress affects the vascular niche for adult hippocam- pal neurogenesis. However, fluoxetine treatment had no impact on capilla- rization in the subgranular zone. We also detected a decrease in hippo- campal volume in the animals as a result of stress, which was mildly altered by fluoxetine treatment. These pronounced changes in vascular supply may explain why the hippocampus is more vulnerable to insults when chronic stress precedes or coincides with other harmful conditions. Reduced microvasculature may also contribute to hippocampal volume decrease in stress-related disorders. V V C 2009 Wiley-Liss, Inc. KEY WORDS: capillary; stereology; antidepressant; neurogenic niche; hippocampal volume INTRODUCTION The importance of the physiological and pathophysiological conse- quences of chronic stress is being increasingly acknowledged, with many interdisciplinary studies showing that repetitive, uncontrollable stress affects well-being and leads to disease (e.g., Maunder, 2005; Das and O’Keefe, 2006; Kyrou et al., 2006; Stojanovich and Marisavljevich, 2008). It is now well documented that chronic stress has a significant impact on the cellular integrity and function of cer- tain brain areas, most notably the limbic structures (McEwen, 2007). Numerous studies demonstrate that chronic stress exposure results in reduced hippocampal volume, dendritic remodeling of pyramidal neurons, suppressed adult neurogenesis, and changes in glial numbers (e.g., Conrad, 2006; Cze ´h et al., 2002, 2006; Gianaros et al., 2007; Joe ¨ls et al., 2007). Paral- lel to these findings, a growing number of studies demonstrate that many of these stress-induced cellular changes can be reversed by antidepressant treatment (e.g., Cze ´h et al., 2001, 2007; Holderbach et al., 2007; Pittenger and Duman, 2008; Reine ´s et al., 2008). In contrast to the intensive efforts that have been made to reveal stress-induced molecular and cel- lular alterations of neurons, little attention has been paid to possible changes in vascularization, which is the major structure for supplying nutrition and oxy- gen to neurons. Experimental evidence suggests that the hippocam- pus is more vulnerable to insults when chronic stress precedes or coincides with other harmful conditions (e.g., Lee et al., 2002; Conrad et al., 2004, 2007; McDonald et al., 2008). However, the exact pathway for how stress influences the survival of injured neu- rons is unclear. It has been proposed that stress is harmful, because glucocorticoids impair the capacity of neurons to survive coincident insults, such as sei- zure, hypoxia-ischemia, hypoglycemia, and oxygen radical generators (Sapolsky, 1996; Lee et al., 2002; Conrad et al., 2007). Another possibility, which has not yet been explored, is that chronic stress may impair vascular supply, which may then result in enhanced vulnerability to additional insults. Indeed, there is functional evidence for impaired cerebral blood flow in the hippocampus of rats exposed to 12 weeks of daily brief immersion in cold water (Endo et al., 1999). However, to our best knowledge, no morphometric analysis exists on possible changes in vascularization of hippocampal tissue after exposure to chronic stress. Here, we used the chronic social defeat paradigm in adult male rats, a paradigm that is regarded as a valua- 1 Clinical Neurobiology Laboratory, German Primate Center, Leibniz Institute for Primate Research, Go ¨ ttingen, Germany; 2 DFG Research Center Molecular Physiology of the Brain (CMPB), University of Go ¨ ttin- gen, Go ¨ ttingen, Germany; 3 Department of Neurology, University Medi- cal Center, Georg-August-University, Go ¨ ttingen, Germany *Correspondence to: Boldizsa ´r Cze ´h, Clinical Neurobiology Laboratory, Leibniz Institute for Primate Research, German Primate Center, Kellner- weg 4, D-37077 Go ¨ ttingen, Germany. E-mail: bczeh@cnl-dpz.de Accepted for publication 10 February 2009 DOI 10.1002/hipo.20599 Published online 27 March 2009 in Wiley InterScience (www.interscience. wiley.com). Abbreviations used: ECS, electroconvulsive seizure; DG, dentate gyrus; mol, molecular layer; GCL, granule cell layer; PBS, phosphate buffered saline; SGZ, subgranular zone; SSRI, selective serotonin reuptake inhibi- tor; VEGF, vascular endothelial growth factor. HIPPOCAMPUS 20:174–185 (2010) V V C 2009 WILEY-LISS, INC.