Effects of Isx-9 and stress on adult hippocampal neurogenesis: Experimental considerations and future perspectives.

The development of synthetic small molecules capable of promoting neuronal fate in stem cells is a promising strategy to prevent the decline of hippocampal function caused by several neurological disorders. Within this context, isoxazole 9 (Isx-9) has been shown to strongly induce cell proliferation and neuronal differentiation in the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG), while also improving hippocampal function in healthy mice. We have recently demonstrated that Isx-9 is able to restore normal neurogenesis levels after procedural stress. Here, we further discuss these findings highlighting the importance of including a naïve group in studies investigating the effects of either restraint stress or mild chronic unpredictable stress (CUS) on adult hippocampal neurogenesis.

The Effects of Ethanol Exposure During Distinct Periods of Brain Development on Oxidative Stress in the Adult Rat Brain.

BACKGROUND: The consumption of alcohol during pregnancy can result in abnormal fetal development and impaired brain function in humans and experimental animal models. Depending on the pattern of consumption, the dose, and the period of exposure to ethanol (EtOH), a variety of structural and functional brain deficits can be observed. METHODS: This study compared the effects of EtOH exposure during distinct periods of brain development on oxidative damage and endogenous antioxidant status in various brain regions of adult female and male Sprague Dawley rats. Pregnant dams and neonatal rats were exposed to EtOH during one of the following time windows: between gestational days (GDs) 1 and 10 (first trimester equivalent); between GDs 11 and 21 (second trimester equivalent); or between postnatal days (PNDs) 4 and 10 (third trimester equivalent). RESULTS: EtOH exposure during any of the 3 trimester equivalents significantly increased lipid peroxidation in both the cornus ammonis (CA) and dentate gyrus (DG) subregions of the hippocampus, while also decreasing the levels of the endogenous antioxidant glutathione in the hippocampal CA and DG subregions as well as the prefrontal cortex of young adult animals (PND 60). CONCLUSIONS: These results indicate that EtOH exposure during restricted periods of brain development can have long-term consequences in the adult brain by dysregulating its redox status. This dysfunction may underlie, at least in part, the long-term alterations in brain function associated with fetal alcohol spectrum disorders.

ISX-9 can potentiate cell proliferation and neuronal commitment in the rat dentate gyrus.

Adult hippocampal neurogenesis can be modulated by various physiological and pathological conditions, including stress, affective disorders, and several neurological conditions. Given the proposed role of this form of structural plasticity in the functioning of the hippocampus (namely learning and memory and affective behaviors), it is believed that alterations in hippocampal neurogenesis might underlie some of the behavioral deficits associated with these psychiatric and neurological conditions. Thus, the search for compounds that can reverse these deficits with minimal side effects has become a recognized priority. In the present study we tested the pro-neurogenic effects of isoxazole 9 (Isx-9), a small synthetic molecule that has been recently identified through the screening of chemical libraries in stem cell-based assays. We found that administration of Isx-9 for 14days was able to potentiate cell proliferation and increase the number of immature neurons in the hippocampal DG of adult rats. In addition, Isx-9 treatment was able to completely reverse the marked reduction in these initial stages of the neurogenic process observed in vehicle-treated animals (which were submitted to repeated handling and exposure to daily intraperitoneal injections). Based on these results, we recommend that future neurogenesis studies that require repeated handling and manipulation of animals should include a naïve (non-manipulated) control to determine the baseline levels of hippocampal cell proliferation and neuronal differentiation. Overall, these findings demonstrate that Isx-9 is a promising synthetic compound for the mitigation of stress-induced deficits in adult hippocampal neurogenesis. Future studies are thus warranted to evaluate the pro-neurogenic properties of Isx-9 in animal models of affective and neurological disorders associated with impaired hippocampal structural plasticity.

The effects of hormones and physical exercise on hippocampal structural plasticity.

The hippocampus plays an integral role in certain aspects of cognition. Hippocampal structural plasticity and in particular adult hippocampal neurogenesis can be influenced by several intrinsic and extrinsic factors. Here we review how hormones (i.e., intrinsic modulators) and physical exercise (i.e., an extrinsic modulator) can differentially modulate hippocampal plasticity in general and adult hippocampal neurogenesis in particular. Specifically, we provide an overview of the effects of sex hormones, stress hormones, and metabolic hormones on hippocampal structural plasticity and adult hippocampal neurogenesis. In addition, we also discuss how physical exercise modulates these forms of hippocampal plasticity, giving particular emphasis on how this modulation can be affected by variables such as exercise regime, duration, and intensity. Understanding the neurobiological mechanisms underlying the modulation of hippocampal structural plasticity by intrinsic and extrinsic factors will impact the design of new therapeutic approaches aimed at restoring hippocampal plasticity following brain injury or neurodegeneration.

Effects of pre-natal alcohol exposure on hippocampal synaptic plasticity: Sex, age and methodological considerations.

The consumption of alcohol during gestation is detrimental to the developing central nervous system (CNS). The severity of structural and functional brain alterations associated with alcohol intake depends on many factors including the timing and duration of alcohol consumption. The hippocampal formation, a brain region implicated in learning and memory, is highly susceptible to the effects of developmental alcohol exposure. Some of the observed effects of alcohol on learning and memory may be due to changes at the synaptic level, as this teratogen has been repeatedly shown to interfere with hippocampal synaptic plasticity. At the molecular level alcohol interferes with receptor proteins and can disrupt hormones that are important for neuronal signaling and synaptic plasticity. In this review we examine the consequences of prenatal and early postnatal alcohol exposure on hippocampal synaptic plasticity and highlight the numerous factors that can modulate the effects of alcohol. We also discuss some potential mechanisms responsible for these changes as well as emerging therapeutic avenues that are beginning to be explored.

The antidepressant-like effect of chronic guanosine treatment is associated with increased hippocampal neuronal differentiation.

Guanosine is a purine nucleoside that occurs naturally in the central nervous system, exerting trophic effects. Given its neuroprotective properties, the potential of guanosine as an antidepressant has been recently examined. Within this context, the present study sought to investigate the effects of chronic treatment with guanosine on the tail suspension test (TST), open field test and adult hippocampal neurogenesis. Swiss mice were administered guanosine for 21 days (5 mg/kg/day, p.o.) and subsequently submitted to the TST and open-field test. Following behavioural testing, animals were killed and the brains were processed for immunohistochemical analyses of hippocampal cell proliferation and neuronal differentiation. Animals treated with guanosine showed a reduction in immobility time in the TST without alterations in locomotor activity, confirming the antidepressant-like effect of this compound. Quantitative microscopic analysis did not reveal significant alterations in the numbers of Ki-67- and proliferating cell nuclear antigen (PCNA)-positive cells in the hippocampal dentate gyrus (DG) of guanosine-treated mice. However, guanosine treatment resulted in a significant increase in the number of immature neurons, as assessed by immunohistochemistry for the neurogenic differentiation protein. Interestingly, this effect was localized to the ventral hippocampal DG, a functionally distinct region of this structure known to regulate emotional and motivational behaviours. Taken together, our results suggest that the antidepressant-like effect of chronic guanosine treatment is associated with an increase in neuronal differentiation, reinforcing the notion that this nucleoside may be an endogenous mood modulator.

Prenatal ethanol exposure impairs temporal ordering behaviours in young adult rats.

Prenatal ethanol exposure (PNEE) causes significant deficits in functional (i.e., synaptic) plasticity in the dentate gyrus (DG) and cornu ammonis (CA) hippocampal sub-regions of young adult male rats. Previous research has shown that in the DG, these deficits are not apparent in age-matched PNEE females. This study aimed to expand these findings and determine if PNEE induces deficits in hippocampal-dependent behaviours in both male and female young adult rats (PND 60). The metric change behavioural test examines DG-dependent deficits by determining whether an animal can detect a metric change between two identical objects. The temporal order behavioural test is thought to rely in part on the CA sub-region of the hippocampus and determines whether an animal will spend more time exploring an object that it has not seen for a larger temporal window as compared to an object that it has seen more recently. Using the liquid diet model of FASD (where 6.6% (v/v) ethanol is provided through a liquid diet consumed ad libitum throughout the entire gestation), we found that PNEE causes a significant impairment in the temporal order task, while no deficits in the DG-dependent metric change task were observed. There were no significant differences between males and females for either task. These results indicate that behaviours relying partially on the CA-region may be more affected by PNEE than those that rely on the DG.

The Benefits of Exercise on Structural and Functional Plasticity in the Rodent Hippocampus of Different Disease Models.

In this review, the benefits of physical exercise on structural and functional plasticity in the hippocampus are discussed. The evidence is clear that voluntary exercise in rats and mice can lead to increases in hippocampal neurogenesis and enhanced synaptic plasticity which ultimately result in improved performance in hippocampal-dependent tasks. Furthermore, in models of neurological disorders, including fetal alcohol spectrum disorders, traumatic brain injury, stroke, and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease exercise can also elicit beneficial effects on hippocampal function. Ultimately this review highlights the multiple benefits of exercise on hippocampal function in both the healthy and the diseased brain.

A comparison of the different animal models of fetal alcohol spectrum disorders and their use in studying complex behaviors.

Prenatal ethanol exposure (PNEE) has been linked to widespread impairments in brain structure and function. There are a number of animal models that are used to study the structural and functional deficits caused by PNEE, including, but not limited to invertebrates, fish, rodents, and non-human primates. Animal models enable a researcher to control important variables such as the route of ethanol administration, as well as the timing, frequency and amount of ethanol exposure. Each animal model and system of exposure has its place, depending on the research question being undertaken. In this review, we will examine the different routes of ethanol administration and the various animal models of fetal alcohol spectrum disorders (FASD) that are commonly used in research, emphasizing their strengths and limitations. We will also present an up-to-date summary on the effects of prenatal/neonatal ethanol exposure on behavior across the lifespan, focusing on learning and memory, olfaction, social, executive, and motor functions. Special emphasis will be placed where the various animal models best represent deficits observed in the human condition and offer a viable test bed to examine potential therapeutics for human beings with FASD.

Long-term exercise is needed to enhance synaptic plasticity in the hippocampus.

Exercise can have many benefits for the body, but it also benefits the brain by increasing neurogenesis, synaptic plasticity, and performance on learning and memory tasks. The period of exercise needed to realize the structural and functional benefits for the brain have not been well delineated, and previous studies have used periods of exercise exposure that range from as little as 3 d to up to 6 mo. In this study, we systematically evaluated the effects of differential running periods (3, 7, 14, 28, and 56 d) on both structural (cell proliferation and maturation) and functional (in vivo LTP) changes in the dentate gyrus of adult male Sprague-Dawley rats. We found that voluntary access to a running wheel for both short- and long-term periods can increase cell proliferation in the adult DG; however, increases in neurogenesis required longer term exposure to exercise. Increases in immature neurons were not observed until animals had been running for a minimum of 14 d. Similarly, short-term periods of wheel running did not facilitate LTP in the DG of adult animals, and reliable increases in LTP were only observed with 56 d of running. These results provide us with a greater understanding of the time course of wheel running access needed to enhance DG function. Furthermore, the results indicate that the new neurons produced in response to exercise in rats do not contribute significantly to synaptic plasticity until they mature.

Impairments in hippocampal synaptic plasticity following prenatal ethanol exposure are dependent on glutathione levels.

Previous studies from our laboratory have shown that prenatal ethanol exposure (PNEE) causes a significant deficit in synaptic plasticity, namely long-term potentiation (LTP), in the dentate gyrus (DG) region of the hippocampus of male rats. PNEE has also been shown to induce an increase in oxidative stress and a reduction in antioxidant capacity in the brains of both male and female animals. In this study the interaction between LTP and the major antioxidant in the brain, glutathione (GSH), is examined. We show that depletion of the intracellular reserves of GSH with diethyl maleate (DEM) reduces LTP in control male, but not female animals, mirroring the effects of PNEE. Furthermore, treatment of PNEE animals with N-acetyl cysteine (NAC), a cysteine donor for the synthesis of GSH, increases GSH levels in the hippocampus and completely restores the deficits in LTP in PNEE males. These results indicate that in males GSH plays a major role in regulating LTP, and that PNEE may cause reductions in LTP by reducing the intracellular pool of this endogenous antioxidant.

Omega-3 fatty acids can reverse the long-term deficits in hippocampal synaptic plasticity caused by prenatal ethanol exposure.

Fetal alcohol spectrum disorders result in long-lasting neurological deficits including decreases in synaptic plasticity and deficits in learning and memory. In this study we examined the effects of prenatal ethanol exposure on hippocampal synaptic plasticity in male and female Sprague-Dawley rats. Furthermore, we looked at the capacity for postnatal dietary intervention to rescue deficits in synaptic plasticity. Animals were fed an omega-3 enriched diet from birth until adulthood (PND55-70) and in vivo electrophysiology was performed by stimulating the medial perforant path input to the dentate gyrus and recording field excitatory post-synaptic potentials. LTP was induced by administering bursts of five 400 Hz pulses as a theta-patterned train of stimuli (200 ms inter-burst interval). Ethanol-exposed adult males, but not females, exhibited a significant reduction in LTP. This deficit in male animals was completely reversed with an omega-3 enriched diet. These results demonstrate that omega-3 fatty acids can have benefits following prenatal neuropathological insults and may be a viable option for alleviating some of the neurological deficits associated with FASD.

Omega-3 supplementation can restore glutathione levels and prevent oxidative damage caused by prenatal ethanol exposure.

Prenatal ethanol exposure (PNEE) causes long-lasting deficits in brain structure and function. In this study, we have examined the effect of PNEE on antioxidant capacity and oxidative stress in the adult brain with particular focus on four brain regions known to be affected by ethanol: cerebellum, prefrontal cortex and hippocampus (cornu ammonis and dentate gyrus subregions). We have utilized a liquid diet model of fetal alcohol spectrum disorders that is supplied to pregnant Sprague-Dawley rats throughout gestation. To examine the therapeutic potential of omega-3 fatty acid supplementation, a subset of animals were provided with an omega-3-enriched diet from birth until adulthood to examine whether these fatty acids could ameliorate any deficits in antioxidant capacity that occurred due to PNEE. Our results showed that PNEE caused a long-lasting decrease in glutathione levels in all four brain regions analyzed that was accompanied by an increase in lipid peroxidation, a marker of oxidative damage. These results indicate that PNEE induces long-lasting changes in the antioxidant capacity of the brain, and this can lead to a state of oxidative stress. Postnatal omega-3 supplementation was able to increase glutathione levels and reduce lipid peroxidation in PNEE animals, partially reversing the effects of alcohol exposure, particularly in the dentate gyrus and the cerebellum. This is the first study where omega-3 supplementation has been shown to have a beneficial effect in PNEE, reducing oxidative stress and enhancing antioxidant capacity.

Effects of Ethanol Exposure during Distinct Periods of Brain Development on Hippocampal Synaptic Plasticity.

Fetal alcohol spectrum disorders occur when a mother drinks during pregnancy and can greatly influence synaptic plasticity and cognition in the offspring. In this study we determined whether there are periods during brain development that are more susceptible to the effects of ethanol exposure on hippocampal synaptic plasticity. In particular, we evaluated how the ability to elicit long-term potentiation (LTP) in the hippocampal dentate gyrus (DG) was affected in young adult rats that were exposed to ethanol during either the 1st, 2nd, or 3rd trimester equivalent. As expected, the effects of ethanol on young adult DG LTP were less severe when exposure was limited to a particular trimester equivalent when compared to exposure throughout gestation. In males, ethanol exposure during the 1st, 2nd or 3rd trimester equivalent did not significantly reduce LTP in the DG. In females, ethanol exposure during either the 1st or 2nd trimester equivalents did not impact LTP in early adulthood, but following exposure during the 3rd trimester equivalent alone, LTP was significantly increased in the female DG. These results further exemplify the disparate effects between the ability to elicit LTP in the male and female brain following perinatal ethanol exposure (PNEE).

Pharmacological Preconditioning with GYKI 52466: A Prophylactic Approach to Neuroprotection.

Some toxins and drugs can trigger lasting neuroprotective mechanisms that enable neurons to resist a subsequent severe insult. This "pharmacological preconditioning" has far-reaching implications for conditions in which blood flow to the brain is interrupted. We have previously shown that in vitro preconditioning with the AMPA receptor antagonist GYKI 52466 induces tolerance to kainic acid (KA) toxicity in hippocampus. This effect persists well after washout of the drug and may be mediated via inverse agonism of G-protein coupled receptors (GPCRs). Given the amplifying nature of metabotropic modulation, we hypothesized that GYKI 52466 may be effective in reducing seizure severity at doses well below those normally associated with adverse side effects. Here we report that pharmacological preconditioning with low-dose GYKI imparts a significant protection against KA-induced seizures in vivo. GYKI (3 mg/kg, s.c.), 90-180 min prior to high-dose KA, markedly reduced seizure scores, virtually abolished all level 3 and level 4 seizures, and completely suppressed KA-induced hippocampal c-FOS expression. In addition, preconditioned animals exhibited significant reductions in high frequency/high amplitude spiking and ECoG power in the delta, theta, alpha, and beta bands during KA. Adverse behaviors often associated with higher doses of GYKI were not evident during preconditioning. The fact that GYKI is effective at doses well-below, and at pre-administration intervals well-beyond previous studies, suggests that a classical blockade of ionotropic AMPA receptors does not underlie anticonvulsant effects. Low-dose GYKI preconditioning may represent a novel, prophylactic strategy for neuroprotection in a field almost completely devoid of effective pharmaceuticals.