Melatonin Prevents Depression but Not Anxiety-like Behavior Produced by the Chemotherapeutic Agent Temozolomide: Implication of Doublecortin Cells and Hilar Oligodendrocytes.

Melatonin is a hormone synthesized by the pineal gland with neuroprotective and neurodevelopmental effects. Also, melatonin acts as an antidepressant by modulating the generation of new neurons in the dentate gyrus of the hippocampus. The positive effects of melatonin on behavior and neural development may suggest it is used for reverting stress but also for the alterations produced by chemotherapeutic drugs influencing behavior and brain plasticity. In this sense, temozolomide, an alkylating/anti-proliferating agent used in treating brain cancer, is associated with decreased cognitive functions and depression. We hypothesized that melatonin might prevent the effects of temozolomide on depression- and anxiety-like behavior by modulating some aspects of the neurogenic process in adult Balb/C mice. Mice were treated with temozolomide (25 mg/kg) for three days of two weeks, followed by melatonin (8 mg/kg) for fourteen days. Temozolomide produced short- and long-term decrements in cell proliferation (Ki67-positive cells: 54.89% and 53.38%, respectively) and intermediate stages of the neurogenic process (doublecortin-positive cells: 68.23% and 50.08%, respectively). However, melatonin prevented the long-term effects of temozolomide with the increased number of doublecortin-positive cells (47.21%) and the immunoreactivity of 2' 3'-Cyclic-nucleotide-3 phosphodiesterase (CNPase: 82.66%), an enzyme expressed by mature oligodendrocytes, in the hilar portion of the dentate gyrus. The effects of melatonin in the temozolomide group occurred with decreased immobility in the forced swim test (45.55%) but not anxiety-like behavior. Thus, our results suggest that melatonin prevents the harmful effects of temozolomide by modulating doublecortin cells, hilar oligodendrocytes, and depression-like behavior tested in the forced swim test. Our study could point out melatonin's beneficial effects for counteracting temozolomide's side effects.

5 Hz of repetitive transcranial magnetic stimulation improves cognition and induces modifications in hippocampal neurogenesis in adult female Swiss Webster mice.

Adult hippocampal neurogenesis is regulated by several stimuli to promote the creation of a reserve that may facilitate coping with environmental challenges. In this regard, repetitive transcranial magnetic stimulation (rTMS), a neuromodulation therapy, came to our attention because in clinical studies it reverts behavioral and cognitive alterations related to changes in brain plasticity. Some preclinical studies emphasize the need to understand the underlying mechanism of rTMS to induce behavioral modifications. In this study, we investigated the effects of rTMS on cognition, neurogenic-associated modifications, and neuronal activation in the hippocampus of female Swiss Webster mice. We applied 5 Hz of rTMS twice a day for 14 days. Three days later, mice were exposed to the behavioral battery. Then, brains were collected and immunostained for Ki67-positive cells, doublecortin-positive (DCX+)-cells, calbindin, c-Fos and FosB/Delta-FosB in the dentate gyrus. Also, we analyzed mossy fibers and CA3 with calbindin immunostaining. Mice exposed to rTMS exhibited cognitive improvement, an increased number of proliferative cells, DCX cells, DCX cells with complex dendrite morphology, c-Fos and immunoreactivity of FosB/Delta-FosB in the granular cell layer. The volume of the granular cell layer, mossy fibers and CA3 in rTMS mice also increased. Interestingly, cognitive improvement correlated with DCX cells with complex dendrite morphology. Also, those DCX cells and calbindin immunoreactivity correlated with c-Fos in the granular cell layer. Our results suggest that 5 Hz of rTMS applied twice a day modify cell proliferation, doublecortin cells, mossy fibers and enhance cognitive behavior in healthy female Swiss Webster mice.

Soluble Factors from Human Olfactory Neural Stem/Progenitor Cells Influence the Fate Decisions of Hippocampal Neural Precursor Cells.

Neurogenesis plays a significant role during adulthood, and the observation that neural stem cells reside in the central nervous system and the olfactory epithelium has attracted attention due to their importance in neuronal regeneration. In addition, soluble factors (SFs) release by neural stem cells may modulate the neurogenic process. Thus, in this study, we identified the SFs released by olfactory human neural stem/progenitor cells (hNS/PCs-OE). These cells express Ki67, nestin, and ßIII-tubulin, indicating their neural lineage. The hNS/PCs-OE also express PSD95 and tau proteins during proliferation, but increased levels are observed after differentiation. Thus, we evaluated the effects of SFs from hNS/PCs-OE on the viability, proliferation, and differentiation potential of adult murine hippocampal neural precursor cells (AHPCs). SFs from hNS/PCs-OE maintain cells in the precursor and proliferative stages and mainly promote the astrocytic differentiation of AHPCs. These effects involved the activation, as measured by phosphorylation, of several proteins (Erk1/2; Akt/PRAS40/GSK3ß and JAK/STAT) involved in key events of the neurogenic process. Moreover, according to the results from the antibody-based microarray approach, among the soluble factors, hNS/PCs-OE produce interleukin-6 (IL-6) and neurotrophin 4 (NT4). However, residual epidermal growth factor (EGF) was also detected. These proteins partially reproduced the effects of SFs from hNS/PCs-OE on AHPCs, and the mechanism underlying these effects is mediated by Src proteins, which have been implicated in EGF-induced transactivation of TrkB receptor. The results of the present study suggest the potential use of SFs from hNS/PCs-OE in controlling the differentiation potential of AHPCs. Thus, the potential clinical relevance of hNS/PCs-OE is worth pursuing.

Vascular endothelial growth factor influences migration and focal adhesions, but not proliferation or viability, of human neural stem/progenitor cells derived from olfactory epithelium.

In humans, new neurons are continuously added in the olfactory epithelium even in the adulthood. The resident neural stem/progenitor cells (hNS/PCs-OE) in the olfactory epithelium are influenced by several growth factors and neurotrophins. Among these modulators the vascular endothelial growth factor (VEGF) has attracted attention due its implicated in cell proliferation, survival and migration of other type of neural/stem progenitor cells. Interestingly, VEGFr2 receptor expression in olfactory epithelium has been described in amphibians but not in humans. Here we show that VEGFr is expressed in the hNS/PCs-OE. We also investigated the effect of VEGF on the hNS/PCs-OE proliferation, viability and migration in vitro. Additionally, pharmacological approaches showed that VEGF (0.5 ng/ml)-stimulated migration of hNS/PCs-OE was blocked with the compound DMH4, which prevents the activation of VEGFr2. Similar effects were found with the inhibitors for Rac (EHT1864) and p38MAPK (SB203850) proteins, respectively. These observations occurred with changes in focal adhesion contacts. However, no effects of VEGF on proliferation or viability were found in hNS/PCs-OE. Our results suggest that hNS/PCs-OE respond to VEGF involving VEGFr2, Rac and p38MAPK.

Human neural stem/progenitor cells derived from the olfactory epithelium express the TrkB receptor and migrate in response to BDNF.

Neurogenesis constitutively occurs in the olfactory epithelium of mammals, including humans. The fact that new neurons in the adult olfactory epithelium derive from resident neural stem/progenitor cells suggests a potential use for these cells in studies of neural diseases, as well as in neuronal cell replacement therapies. In this regard, some studies have proposed that the human olfactory epithelium is a source of neural stem/progenitor cells for autologous transplantation. Although these potential applications are interesting, it is important to understand the cell biology and/or whether human neural stem/progenitor cells in the olfactory epithelium sense external signals, such as brain-derived neurotrophic factor (BDNF), that is also found in other pro-neurogenic microenvironments. BDNF plays a key role in several biological processes, including cell migration. Thus, we characterized human neural stem/progenitor cells derived from the olfactory epithelium (hNS/PCs-OE) and studied their in vitro migratory response to BDNF. In the present study, we determined that hNS/PCs-OE express the protein markers Nestin, Sox2, Ki67 and ßIII-tubulin. Moreover, the doubling time of hNS/PCs-OE was approximately 38h. Additionally, we found that hNS/PCs-OE express the BDNF receptor TrkB, and pharmacological approaches showed that the BDNF-induced (40ng/ml) migration of differentiated hNS/PCs-OE was affected by the compound K252a, which prevents TrkB activation. This observation was accompanied by changes in the number of vinculin adhesion contacts. Our results suggest that hNS/PCs-OE exhibit a migratory response to BDNF, accompanied by the turnover of adhesion contacts.

Resveratrol Enhances Neuroplastic Changes, Including Hippocampal Neurogenesis, and Memory in Balb/C Mice at Six Months of Age.

Resveratrol (RVTL) is a flavonoid found in red wine and has been publicized heavily as an anti-aging compound. Indeed, basic research confirms that although there is much hype in the promotion of RVTL, flavonoids such as RVTL have a wide range of biological effects. We here investigated the effects of RVTL treatment on hippocampal plasticity and memory performance in female Balb/C mice, a strain with low baseline levels of adult neurogenesis. Two weeks of treatment with RVTL (40 mg/kg) induced the production of new neurons in vivo by increasing cell survival and possibly precursor cell proliferation. In addition, RVTL decreased the number of apoptotic cells. The number of doublecortin (DCX)-expressing intermediate cells was increased. RVTL stimulated neuronal differentiation in vitro without effects on proliferation. In the dentate gyrus, RVTL promoted the formation and maturation of spines on granule cell dendrites. RVTL also improved performance in the step down passive avoidance test. The RVTL-treated mice showed increase in the levels of two key signaling proteins, phospho-Akt and phospho-PKC, suggesting the involvement of these signaling pathways. Our results support the vision that flavonoids such as resveratrol deserve further examination as plasticity-inducing compounds in the context of successful cognitive aging.

Regulación de la neurogénesis hipocámpica por los estrógenos: su relación con la depresión / Regulation of adult hippocampal neurogenesis by estrogens: relationship to depression

Estrogens produce a wide range of biological effects throughout the body, including the Central Nervous System (CNS). In the brain, besides acting as neuroprotective agents, estrogens play an important role in many neuronal processes and certain psychiatric disorders such as depression. The precise mechanism by which estrogens induce their positive effects on depressive disorders has not been elucidated; however, it is known that estrogens act on the CNS through the activation of specific receptors. These actions occur in genomic and non-genomics mechanisms through the modulation of synthesis and metabolism of neurotransmitters, neuropeptides, neurosteroids and influencing the morphological features of neurons and synaptic function. In addition, it is known that estrogens can act as modulators of processes related to neuroplasticity and neurogenesis. Adult hippocampal neurogenesis is a neuroplastic process that is affected by antidepressant drugs. These drugs increase the number of new neurons following a temporal course that correlates within the time in which antidepressants cause a behavioral improvement in rodents and in humans. Interestingly, whereas the behavioral antidepressant effects require 2-4 weeks to appear, after treatment initiation, estrogen reduce the depressive-like behavior and induce cell proliferation in terms of days. Thus, antidepressant drugs and the estrogens replacement during the adulthood could influence in a similar manner the new neuron formation. Furthermore, recent works have indicated that the combination of antidepressants plus estrogens could exert beneficial actions at lower doses of estrogens (physiological range). This evidence is important due to the combination of non-effective doses of antidepressants plus estrogens could decrease the side-effects of both compounds, and facilitate the behavioral action of antidepressant drugs shortening the latency to onset their action. The present review discusses recent information about the implication of estrogens in depression, and on their effects as positive regulators of new neuron formation in the adult hippocampus. In addition, we will review the possible implication of last effect of estrogens on their antidepressant effects.

Los estrógenos producen una amplia gama de efectos biológicos en todo el cuerpo, incluyendo el Sistema Nervioso Central (SNC). En el cerebro, además de actuar como agentes neuroprotectores, los estrógenos desempeñan un papel importante en la regulación de procesos neuronales constituyéndose así como posibles factores relacionados con la etiología de algunos trastornos neuropsiquiátricos, tales como la depresión. Durante los últimos años se ha generado evidencia de la relación existente entre los niveles fisiológicos de los estrógenos y el desarrollo de episodios depresivos. Por otra parte, los estrógenos tienen un papel importante en la inducción de cambios a nivel de la plasticidad neuronal y de la neurogénesis en el hipocampo adulto. A este respecto se ha observado que los estrógenos regulan el desarrollo, la maduración y la sobrevivencia de las nuevas neuronas en el cerebro adulto, de la misma manera que lo hacen los tratamientos antidepresivos. Los efectos de los estrógenos sobre la neurogénesis y la plasticidad neuronal podrían estar regulados por los receptores a estrógenos, tanto el receptor alfa (REα), como el receptor beta (REβ). Ambos subtipos de receptores se expresan en el hipocampo del cerebro adulto. Así mismo, el hipocampo es una estructura que participa en procesos cognitivos y de memoria y existe evidencia que muestra su participación en la etiología de la depresión y sobre el efecto de los fármacos antidepresivos. La neurogénesis ha sido considerada como un proceso dinámico por medio del cual se forman neuronas funcionales. De tal modo que este proceso también involucra los eventos de sobrevivencia, maduración dendrítica y axonal, así como el establecimiento de conexiones sinápticas para la integración final de las nuevas neuronas en los circuitos neuronales existentes, eventos que son modulados por los fármacos antidepresivos. En el presente artículo se revisa información reciente acerca de los efectos de los estrógenos sobre la depresión y sobre su relación con la neurogénesis hipocámpica.