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Venlafaxine reverses decreased proliferation in the subventricular zone in a rat model of early life stress
Behavioural Brain Research 292 (2015) 79–82
Contents lists available at ScienceDirect
Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr
Venlafaxine reverses decreased proliferation in the subventricular zone in a rat model of early life stress Eva Martisova, Bárbara Aisa, Rosa M. Tordera, Elena Puerta, Maite Solas, María J. Ramirez ∗ Department of Pharmacology and Toxicology, University of Navarra, IdiSNA, Navarra Institute for Health Research, 31008 Pamplona, Spain
h i g h l i g h t s • Neonatal stress induced depressive-like behavior and cognitive deficits. • Neonatal stress induced decrease in proliferation in the subventricular zone. • Venlafaxine reversed all deleterious effects of chronic stress.
a r t i c l e
i n f o
Article history: Received 5 May 2015 Received in revised form 25 May 2015 Accepted 30 May 2015 Available online 5 June 2015 Keywords: Stress Maternal separation Corticosterone Glucocorticoid receptor Depression Experimental model of AD
a b s t r a c t It is believed that glucocorticoids control the proliferation of neural progenitor cells, and this process is highly involved in mood disorders and cognitive processes. Using the maternal separation model of chronic neonatal stress, it has been found that stress induced depressive-like behavior, cognitive deficits and a decrease in proliferation in the subventricular zone (SVZ). Venlafaxine reversed all deleterious effects of chronic stress by modulating HPA activity. These outcomes suggest modulation of stressmediated glucocorticoid secretion as a target for the treatment of mood disorders and neurodegenerative processes. © 2015 Elsevier B.V. All rights reserved.
Stress and glucocorticoids are known to decrease neurogenesis within the hippocampal dentate gyrus and to induce behavioral phenotypes mimicking those seen in depression [1]. However, throughout life, neural stem cells continue to proliferate not only in the hippocampal dentate gyrus, but also in the subventricular zone (SVZ) of the lateral ventricle [2]. Precursors of the SVZ migrate through the rostral migratory stream into the olfactory bulb. Interestingly, the olfactory bulbectomized rat has been proposed as an animal model of depression [3]. In contrast to the dentate gyrus, in which a considerable amount of available literature deals on the effects of stress and antidepressant drugs on cell proliferation, few and contradictory results [4,5] have been described on the effects of chronic stress or antidepressant treatment on proliferation in the SVZ.
∗ Corresponding author at: Department of Pharmacology, University of Navarra, C/ Irunlarrea, 1, 31008 Pamplona, Spain. Fax: +34 948425649. E-mail address: [email protected] (M.J. Ramirez). http://dx.doi.org/10.1016/j.bbr.2015.05.059 0166-4328/© 2015 Elsevier B.V. All rights reserved.
In order to address this issue, in the present work it has been used the maternal separation (MS) model, an animal paradigm designed to mimic repeated exposure to stress during early life, resulting in adult animals with behavioral (depressive-like) and neuroendocrine signs of elevated stress reactivity [6–8]. The combined serotonin-norepinephrine reuptake inhibitor, venlafaxine, has been chosen as it has demonstrated better short-term efficacy than other antidepressants in epidemiological pooled analyses [9]. All the experiments were carried out in strict compliance with the recommendations of the EU (Directive 2010/63/EU on the protection of animals used for scientific purposes). Timed-pregnant Wistar rats were provided on gestation day 16 from Charles River Laboratories (Portage, MI, USA), individually housed in a temperature – (21 ± 1 ◦ C) and humidity – (55 ± 5%) controlled room on a 12-h light/dark cycle (lights on at 8:00 a.m.) with food and water freely available. Behavioral experiments were conducted between 9:00 a.m. and 1:00 p.m. Every effort was made to minimize the number of animals used and their suffering. On postnatal day (PND) 2, pups were sexed and randomly assigned to the control group
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E. Martisova et al. / Behavioural Brain Research 292 (2015) 79–82
Fig. 1. Experimental design. From PND 2 to 21 inclusive MS procedure was carried out, i.e., pups were separated from their dam for 180 min/day. Rats were weaned on PND 23. Beginning on PND 60, saline or venlafaxine (20 mg/kg, p.o.) were administered daily for 15 days to control and MS rats. Cognition and depressive-like behavior were studied using the NORT and Porsolt forced swimming test, respectively. To study proliferation, rats received two separate i.p. injections of BrdU (PND 74) 100 mg/kg. Animals were sacrificed 24 h after the second BrdU injection (PND 75). PND: postnatal day; BrdU: 5-bromo-2-deoxyuridine.
(animal facility rearing), or MS, pups separated from their dam for 180 min from PNDs 2–21 inclusive (Fig. 1). Rats were weaned on PND 23 and, due to the high variability of females in behavioral tasks, only males were chosen for the present work. Four animals were placed in each cage and all subsequent experiments were performed in adulthood (60–75 days). Beginning on PND 60, saline or venlafaxine (20 mg/kg, p.o.) were administered daily for 15 days to control and MS rats (Fig. 1). The dose of venlafaxine was chosen according to previous works [10]. Depressive-like behavior and cognition were studied using the Porsolt forced swimming test and the novel object recognition test (NORT), respectively. Forced swimming test procedure was carried out as described by Porsolt et al. [11]. Two swimming sessions were conducted: an initial 15min pretest followed 24 h later by a 5-min test, when immobility time was measured. All animals were placed individually in a vertical Plexiglas cylinder (height: 45 cm, diameter: 19 cm) filled with 26 ◦ C water at a depth that makes it impossible to reach the bottom with hind paws (28–30 cm). The object recognition test was performed as previously described [6]. The open field consisted of a square open field (65 cm × 65 cm × 45 cm) made of black wood. On the previous day to the experiment, animals were familiarized with the square during 30 min. During the first trial two identical objects, were placed within the chamber and the rat was allowed to freely explore during 5 min. It was considered that the animal was exploring the object when the head of the rat was oriented toward the object with its nose within 2 cm of the object. One hour later a second trial took place, in which one object was replaced by a different one, and exploration was again scored for 5 min. Results were expressed as percentage of time spent with the novel object with respect to the total exploration time (discrimination index). In the NORT results were expressed as percentage of time spent with the novel object compared to the total exploration time (discrimination index). Horizontal locomotor activity was also measured using a video tracking system (Ethovision 3.0, Noldus Information Technology B.V., The Netherlands). To study proliferation in the SVZ, rats received two separate i.p. injections of 5-bromo-2-deoxyuridine (BrdU), 100 mg/kg. Animals were sacrificed 24 h after the second BrdU injection (Fig. 1). Frozen microtome sections were cut coronally (40 m) through entire SVZ. A stereological approach was applied; analysis was performed in every 8th section with a separation of 320 m between each section. Proliferation was performed following the diaminobenzidine (DAB) peroxidase immunohistochemistry method, as previously described [12]. Since BrdU-positive cells in the SVZ occurred predominantly in clusters and unevenly distributed along the SVZ, the total area of BrdU immunoreactivity in the SVZ lining the lat-
eral ventricle adjacent to the striatum was determined. In each section, the total length of the SVZ from both hemispheres was captured by an AxioCam ICc3 camera on Zeiss Axio Imager M1 upright microscope at 20 × magnification using a digital image processing software (AxioVision Release 4.6.3, GmbH). Illumination, contrast and brightness were kept consistent for each image. The pixel area ˆ image software (Olympus Soft was analysed with the AnalySISD Imaging Solutions GmbH, Germany). Pixel density distribution was standardized for all sections. Pixel area was converted into micrometer squared (m2 ). The mean area of BrdU immunoreactivity in the SVZ of the MS animals was expressed as a percentage of the mean area of BrdU immunoreactivity in SVZ of control animals. Plasma corticosterone was measured using a commercially available radioinmmunoassay kit (Coat-A-Count Rat Corticosterone, Siemens). Glucocorticoid receptors (GR) were measured by western blotting performed in hippocampal samples using a monoclonal antibody GR (Santa Cruz Biotechnology). Data were analysed by two-way analysis of variance ANOVA (rearing × treatment), followed by Student’s t-test adjusted by Bonferroni correction. Normality was checked by Shapiro–Wilk’s test (p > 0.05). For all analyses, post hoc comparisons were conducted if appropriate, using Tukey protected least significance test. Data analyses were performed using the Statistical Program for the Social Sciences (SPSS for Windows, 15.0). In the Porsolt forced swimming test (Fig. 2A), two-way ANOVA indicated a significant increase in immobility time in MS rats compared with controls that was reversed after treatment with venlafaxine [F(1,39) = 3.445, p < 0.05, n = 10]. MS rats exhibited memory impairments (Fig. 2B), as shown by a significantly lower discrimination index compared with controls, that were reversed by venlafaxine treatment [F(1,39 ) = 4.345, p < 0.05, n = 10]. Locomotor activity was not modified either by rearing or by antidepressant treatment (F(1.39 ) = 1.114, p = 0.298). These results are in accordance to previous reported works in which MS rats show depressive-like behavior and cognitive deficits in adulthood [6,13]. It has been shown that alterations in the behavioral phenotype associated to stress are related to the increase HPA axis responsiveness to stressors [14]. In agreement with previous studies [13], in the present study (Fig. 2C), there was a significant increase in corticosterone levels in MS animals compared to control animals which was reversed by treatment with venlafaxine [F(1.31 ) = 24.087, p < 0.01, n = 8 per group]. HPA axis hyperactivity is probably due to a reduced GR-mediated negative feedback, which in turn increases production and secretion of glucocorticoids. Indeed, normalizing GR actions by using a GR antagonist (mifepristone) leads to normalization of depressive-like phenotype in MS [6]. Following this
E. Martisova et al. / Behavioural Brain Research 292 (2015) 79–82
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Fig. 2. Early life stress (MS) induced depressive-like behavior in the Portsolt swimming test (A), cognitive deficits in the novel object recognition test (NORT, B) and hyperactivity of the HPA axis as shown by corticosterone levels (C) and glucocorticoid (GR) expression in the hippocampus (D) that was counteracted by venlafaxine (VEN) treatment. MS: maternal separation. Ven: venlafaxine. Sal: saline. Bars indicate standard errors. Two way ANOVA, * significant differences to controls; † significant differences to MS.
hypothesis (Fig. 2D), MS produced a significant decrease in GR expression that was reversed by chronic treatment with venlafaxine [F(1.27 ) = 4.353, p < 0.05, n = 7 per group]. As shown in Fig. 3, MS produced a significant decrease in cell proliferation and treatment with venlafaxine reversed this decrease in cell proliferation [F(1.19) = 9.983, p < 0.005, n = 5 per group]. Using the forced swimming test models of chronic stress in adulthood,
Hitoshi et al. [4] described also a decrease in the number of neural stem cells in the SVZ that was reversed by treatment with fluoxetine or imipramine. Noteworthy, the effect of antidepressant treatment on SVZ neurogenesis is quite controversial, since both decreases [5] and increases [15] have been observed. It is believed that glucocorticoids may control the proliferation and/or maturation of neural progenitor cells [16]. Basal levels of
Fig. 3. Effects of maternal separation (MS) and chronic venlafaxine (VEN) treatment on cell proliferation in the subventricular zone. In (A), representative picture of the subventricular zone. In (B), representative pictures and quantification of results. The mean area of BrdU immunoreactivity in the SVZ of the MS and venlafaxine treated rats is expressed as a percentage of BrdU immunoreactivity in the SVZ of control rats. Two way ANOVA, * significant differences to controls; † significant differences to MS. Scale bar = 100 m.
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glucocorticoids are essential for neuronal development, plasticity, and survival, while stress-mediated levels of glucocorticoids produce neuronal loss [17]. Lau et al. [15] showed that corticosterone decreased cell proliferation in SVZ, an effect attenuated by paroxetine. Therefore venlafaxine, by modulating HPA activity, could contribute to the restoration of a decreased proliferation induced by stress. However, considering the implication of serotonin in cell proliferation in the SVZ [18] and the role of Venlafaxine as serotonin-norepinephrine reuptake inhibitor, the involvement of serotonergic system cannot be ruled out. The neural progenitor cells located in the SVZ may provide a cellular reservoir for replacement of cells lost during normal cell turnover and after brain injury. Although the implication of adult neurogenesis for brain function is still under intense investigation, alterations in neurogenesis have been reported during aging and in age-related neurodegenerative diseases, including Alzheimer disease (AD) [19,20]. Interestingly, it has been demonstrated that the MS animal model shows the AD-principal hallmarks (memory impairment, tau hyperphosphorylation and amyloid pathology) [13]. In addition, it has already been described the involvement of cell proliferation in the SVZ and changes in the function of its projecting area, the olfactory bulbs, in other experimental models of AD [21]. Moreover, in vivo studies in animal models, in combination with computational approaches, have so far uncovered an important role in olfactory bulb and hippocampus-dependent learning and memory tasks [22]. Furthermore, when adult neurogenesis is experimentally ablated, changes reminiscent of those seen during aging and in AD are observed [20], such as defects in hippocampus-dependent learning and memory, olfactory deficits and olfactory bulb atrophy [23]. Even more, patients exhibiting mood disorders, depression, or psychiatric syndromes often show alteration in structures related to olfactory function and olfactory performance is also reduced in depressed patients [24]. In fact, it has been suggested that identification of olfactory dysfunction at the preclinical and early stages of the disease is a potentially useful method to accomplish early detection of AD [25]. Altogether, the present outcomes highlight a purported role of stress-mediated decline of adult proliferation and suggest modulation of stressmediated glucocorticoid secretion as a target for the treatment of mood disorders and neurodegenerative diseases. Conflict of interest None of the authors have any actual or potential conflict of interest including any financial, consulting, personal or other relationships with other people or organizations within three years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work. Acknowledgements This work has been supported by the Newmood integrated project (EC, LSHM-CT-2004-503474) and FIS (PI10/01748). References [1] J.C. Garza, M. Guo, W. Zhang, X.Y. Lu, Leptin restores adult hippocampal neurogenesis in a chronic unpredictable stress model of depression and
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Contents lists available at ScienceDirect
Behavioural Brain Research journal homepage: www.elsevier.com/locate/bbr
Venlafaxine reverses decreased proliferation in the subventricular zone in a rat model of early life stress Eva Martisova, Bárbara Aisa, Rosa M. Tordera, Elena Puerta, Maite Solas, María J. Ramirez ∗ Department of Pharmacology and Toxicology, University of Navarra, IdiSNA, Navarra Institute for Health Research, 31008 Pamplona, Spain
h i g h l i g h t s • Neonatal stress induced depressive-like behavior and cognitive deficits. • Neonatal stress induced decrease in proliferation in the subventricular zone. • Venlafaxine reversed all deleterious effects of chronic stress.
a r t i c l e
i n f o
Article history: Received 5 May 2015 Received in revised form 25 May 2015 Accepted 30 May 2015 Available online 5 June 2015 Keywords: Stress Maternal separation Corticosterone Glucocorticoid receptor Depression Experimental model of AD
a b s t r a c t It is believed that glucocorticoids control the proliferation of neural progenitor cells, and this process is highly involved in mood disorders and cognitive processes. Using the maternal separation model of chronic neonatal stress, it has been found that stress induced depressive-like behavior, cognitive deficits and a decrease in proliferation in the subventricular zone (SVZ). Venlafaxine reversed all deleterious effects of chronic stress by modulating HPA activity. These outcomes suggest modulation of stressmediated glucocorticoid secretion as a target for the treatment of mood disorders and neurodegenerative processes. © 2015 Elsevier B.V. All rights reserved.
Stress and glucocorticoids are known to decrease neurogenesis within the hippocampal dentate gyrus and to induce behavioral phenotypes mimicking those seen in depression [1]. However, throughout life, neural stem cells continue to proliferate not only in the hippocampal dentate gyrus, but also in the subventricular zone (SVZ) of the lateral ventricle [2]. Precursors of the SVZ migrate through the rostral migratory stream into the olfactory bulb. Interestingly, the olfactory bulbectomized rat has been proposed as an animal model of depression [3]. In contrast to the dentate gyrus, in which a considerable amount of available literature deals on the effects of stress and antidepressant drugs on cell proliferation, few and contradictory results [4,5] have been described on the effects of chronic stress or antidepressant treatment on proliferation in the SVZ.
∗ Corresponding author at: Department of Pharmacology, University of Navarra, C/ Irunlarrea, 1, 31008 Pamplona, Spain. Fax: +34 948425649. E-mail address: [email protected] (M.J. Ramirez). http://dx.doi.org/10.1016/j.bbr.2015.05.059 0166-4328/© 2015 Elsevier B.V. All rights reserved.
In order to address this issue, in the present work it has been used the maternal separation (MS) model, an animal paradigm designed to mimic repeated exposure to stress during early life, resulting in adult animals with behavioral (depressive-like) and neuroendocrine signs of elevated stress reactivity [6–8]. The combined serotonin-norepinephrine reuptake inhibitor, venlafaxine, has been chosen as it has demonstrated better short-term efficacy than other antidepressants in epidemiological pooled analyses [9]. All the experiments were carried out in strict compliance with the recommendations of the EU (Directive 2010/63/EU on the protection of animals used for scientific purposes). Timed-pregnant Wistar rats were provided on gestation day 16 from Charles River Laboratories (Portage, MI, USA), individually housed in a temperature – (21 ± 1 ◦ C) and humidity – (55 ± 5%) controlled room on a 12-h light/dark cycle (lights on at 8:00 a.m.) with food and water freely available. Behavioral experiments were conducted between 9:00 a.m. and 1:00 p.m. Every effort was made to minimize the number of animals used and their suffering. On postnatal day (PND) 2, pups were sexed and randomly assigned to the control group
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Fig. 1. Experimental design. From PND 2 to 21 inclusive MS procedure was carried out, i.e., pups were separated from their dam for 180 min/day. Rats were weaned on PND 23. Beginning on PND 60, saline or venlafaxine (20 mg/kg, p.o.) were administered daily for 15 days to control and MS rats. Cognition and depressive-like behavior were studied using the NORT and Porsolt forced swimming test, respectively. To study proliferation, rats received two separate i.p. injections of BrdU (PND 74) 100 mg/kg. Animals were sacrificed 24 h after the second BrdU injection (PND 75). PND: postnatal day; BrdU: 5-bromo-2-deoxyuridine.
(animal facility rearing), or MS, pups separated from their dam for 180 min from PNDs 2–21 inclusive (Fig. 1). Rats were weaned on PND 23 and, due to the high variability of females in behavioral tasks, only males were chosen for the present work. Four animals were placed in each cage and all subsequent experiments were performed in adulthood (60–75 days). Beginning on PND 60, saline or venlafaxine (20 mg/kg, p.o.) were administered daily for 15 days to control and MS rats (Fig. 1). The dose of venlafaxine was chosen according to previous works [10]. Depressive-like behavior and cognition were studied using the Porsolt forced swimming test and the novel object recognition test (NORT), respectively. Forced swimming test procedure was carried out as described by Porsolt et al. [11]. Two swimming sessions were conducted: an initial 15min pretest followed 24 h later by a 5-min test, when immobility time was measured. All animals were placed individually in a vertical Plexiglas cylinder (height: 45 cm, diameter: 19 cm) filled with 26 ◦ C water at a depth that makes it impossible to reach the bottom with hind paws (28–30 cm). The object recognition test was performed as previously described [6]. The open field consisted of a square open field (65 cm × 65 cm × 45 cm) made of black wood. On the previous day to the experiment, animals were familiarized with the square during 30 min. During the first trial two identical objects, were placed within the chamber and the rat was allowed to freely explore during 5 min. It was considered that the animal was exploring the object when the head of the rat was oriented toward the object with its nose within 2 cm of the object. One hour later a second trial took place, in which one object was replaced by a different one, and exploration was again scored for 5 min. Results were expressed as percentage of time spent with the novel object with respect to the total exploration time (discrimination index). In the NORT results were expressed as percentage of time spent with the novel object compared to the total exploration time (discrimination index). Horizontal locomotor activity was also measured using a video tracking system (Ethovision 3.0, Noldus Information Technology B.V., The Netherlands). To study proliferation in the SVZ, rats received two separate i.p. injections of 5-bromo-2-deoxyuridine (BrdU), 100 mg/kg. Animals were sacrificed 24 h after the second BrdU injection (Fig. 1). Frozen microtome sections were cut coronally (40 m) through entire SVZ. A stereological approach was applied; analysis was performed in every 8th section with a separation of 320 m between each section. Proliferation was performed following the diaminobenzidine (DAB) peroxidase immunohistochemistry method, as previously described [12]. Since BrdU-positive cells in the SVZ occurred predominantly in clusters and unevenly distributed along the SVZ, the total area of BrdU immunoreactivity in the SVZ lining the lat-
eral ventricle adjacent to the striatum was determined. In each section, the total length of the SVZ from both hemispheres was captured by an AxioCam ICc3 camera on Zeiss Axio Imager M1 upright microscope at 20 × magnification using a digital image processing software (AxioVision Release 4.6.3, GmbH). Illumination, contrast and brightness were kept consistent for each image. The pixel area ˆ image software (Olympus Soft was analysed with the AnalySISD Imaging Solutions GmbH, Germany). Pixel density distribution was standardized for all sections. Pixel area was converted into micrometer squared (m2 ). The mean area of BrdU immunoreactivity in the SVZ of the MS animals was expressed as a percentage of the mean area of BrdU immunoreactivity in SVZ of control animals. Plasma corticosterone was measured using a commercially available radioinmmunoassay kit (Coat-A-Count Rat Corticosterone, Siemens). Glucocorticoid receptors (GR) were measured by western blotting performed in hippocampal samples using a monoclonal antibody GR (Santa Cruz Biotechnology). Data were analysed by two-way analysis of variance ANOVA (rearing × treatment), followed by Student’s t-test adjusted by Bonferroni correction. Normality was checked by Shapiro–Wilk’s test (p > 0.05). For all analyses, post hoc comparisons were conducted if appropriate, using Tukey protected least significance test. Data analyses were performed using the Statistical Program for the Social Sciences (SPSS for Windows, 15.0). In the Porsolt forced swimming test (Fig. 2A), two-way ANOVA indicated a significant increase in immobility time in MS rats compared with controls that was reversed after treatment with venlafaxine [F(1,39) = 3.445, p < 0.05, n = 10]. MS rats exhibited memory impairments (Fig. 2B), as shown by a significantly lower discrimination index compared with controls, that were reversed by venlafaxine treatment [F(1,39 ) = 4.345, p < 0.05, n = 10]. Locomotor activity was not modified either by rearing or by antidepressant treatment (F(1.39 ) = 1.114, p = 0.298). These results are in accordance to previous reported works in which MS rats show depressive-like behavior and cognitive deficits in adulthood [6,13]. It has been shown that alterations in the behavioral phenotype associated to stress are related to the increase HPA axis responsiveness to stressors [14]. In agreement with previous studies [13], in the present study (Fig. 2C), there was a significant increase in corticosterone levels in MS animals compared to control animals which was reversed by treatment with venlafaxine [F(1.31 ) = 24.087, p < 0.01, n = 8 per group]. HPA axis hyperactivity is probably due to a reduced GR-mediated negative feedback, which in turn increases production and secretion of glucocorticoids. Indeed, normalizing GR actions by using a GR antagonist (mifepristone) leads to normalization of depressive-like phenotype in MS [6]. Following this
E. Martisova et al. / Behavioural Brain Research 292 (2015) 79–82
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Fig. 2. Early life stress (MS) induced depressive-like behavior in the Portsolt swimming test (A), cognitive deficits in the novel object recognition test (NORT, B) and hyperactivity of the HPA axis as shown by corticosterone levels (C) and glucocorticoid (GR) expression in the hippocampus (D) that was counteracted by venlafaxine (VEN) treatment. MS: maternal separation. Ven: venlafaxine. Sal: saline. Bars indicate standard errors. Two way ANOVA, * significant differences to controls; † significant differences to MS.
hypothesis (Fig. 2D), MS produced a significant decrease in GR expression that was reversed by chronic treatment with venlafaxine [F(1.27 ) = 4.353, p < 0.05, n = 7 per group]. As shown in Fig. 3, MS produced a significant decrease in cell proliferation and treatment with venlafaxine reversed this decrease in cell proliferation [F(1.19) = 9.983, p < 0.005, n = 5 per group]. Using the forced swimming test models of chronic stress in adulthood,
Hitoshi et al. [4] described also a decrease in the number of neural stem cells in the SVZ that was reversed by treatment with fluoxetine or imipramine. Noteworthy, the effect of antidepressant treatment on SVZ neurogenesis is quite controversial, since both decreases [5] and increases [15] have been observed. It is believed that glucocorticoids may control the proliferation and/or maturation of neural progenitor cells [16]. Basal levels of
Fig. 3. Effects of maternal separation (MS) and chronic venlafaxine (VEN) treatment on cell proliferation in the subventricular zone. In (A), representative picture of the subventricular zone. In (B), representative pictures and quantification of results. The mean area of BrdU immunoreactivity in the SVZ of the MS and venlafaxine treated rats is expressed as a percentage of BrdU immunoreactivity in the SVZ of control rats. Two way ANOVA, * significant differences to controls; † significant differences to MS. Scale bar = 100 m.
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glucocorticoids are essential for neuronal development, plasticity, and survival, while stress-mediated levels of glucocorticoids produce neuronal loss [17]. Lau et al. [15] showed that corticosterone decreased cell proliferation in SVZ, an effect attenuated by paroxetine. Therefore venlafaxine, by modulating HPA activity, could contribute to the restoration of a decreased proliferation induced by stress. However, considering the implication of serotonin in cell proliferation in the SVZ [18] and the role of Venlafaxine as serotonin-norepinephrine reuptake inhibitor, the involvement of serotonergic system cannot be ruled out. The neural progenitor cells located in the SVZ may provide a cellular reservoir for replacement of cells lost during normal cell turnover and after brain injury. Although the implication of adult neurogenesis for brain function is still under intense investigation, alterations in neurogenesis have been reported during aging and in age-related neurodegenerative diseases, including Alzheimer disease (AD) [19,20]. Interestingly, it has been demonstrated that the MS animal model shows the AD-principal hallmarks (memory impairment, tau hyperphosphorylation and amyloid pathology) [13]. In addition, it has already been described the involvement of cell proliferation in the SVZ and changes in the function of its projecting area, the olfactory bulbs, in other experimental models of AD [21]. Moreover, in vivo studies in animal models, in combination with computational approaches, have so far uncovered an important role in olfactory bulb and hippocampus-dependent learning and memory tasks [22]. Furthermore, when adult neurogenesis is experimentally ablated, changes reminiscent of those seen during aging and in AD are observed [20], such as defects in hippocampus-dependent learning and memory, olfactory deficits and olfactory bulb atrophy [23]. Even more, patients exhibiting mood disorders, depression, or psychiatric syndromes often show alteration in structures related to olfactory function and olfactory performance is also reduced in depressed patients [24]. In fact, it has been suggested that identification of olfactory dysfunction at the preclinical and early stages of the disease is a potentially useful method to accomplish early detection of AD [25]. Altogether, the present outcomes highlight a purported role of stress-mediated decline of adult proliferation and suggest modulation of stressmediated glucocorticoid secretion as a target for the treatment of mood disorders and neurodegenerative diseases. Conflict of interest None of the authors have any actual or potential conflict of interest including any financial, consulting, personal or other relationships with other people or organizations within three years of beginning the submitted work that could inappropriately influence, or be perceived to influence, their work. Acknowledgements This work has been supported by the Newmood integrated project (EC, LSHM-CT-2004-503474) and FIS (PI10/01748). References [1] J.C. Garza, M. Guo, W. Zhang, X.Y. Lu, Leptin restores adult hippocampal neurogenesis in a chronic unpredictable stress model of depression and
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