Maternal separation prior to neonatal hypoxia-ischemia: Impact on emotional aspects of behavior and markers of synaptic plasticity in hippocampus

Pre- and Post-Synaptic protein in the major depressive Disorder: From neurobiology to therapeutic targets

Major depressive disorder (MDD) has demonstrated its negative impact on various aspects of the lives of those affected. Although several therapies have been developed over the years, it remains a challenge for mental health professionals. Thus, understanding the pathophysiology of MDD is necessary to improve existing treatment options or seek new therapeutic alternatives. Clinical and preclinical studies in animal models of depression have shown the involvement of synaptic plasticity in both the development of MDD and the response to available drugs. However, synaptic plasticity involves a cascade of events, including the action of presynaptic proteins such as synaptophysin and synapsins and postsynaptic proteins such as postsynaptic density-95 (PSD-95). Additionally, several factors can negatively impact the process of spinogenesis/neurogenesis, which are related to many outcomes, including MDD. Thus, this narrative review aims to deepen the understanding of the involvement of synaptic formations and their components in the pathophysiology and treatment of MDD.

Environmental enrichment initiated in adolescence restores the reduced expression of synaptophysin and GFAP in the hippocampus of chronically stressed rats in a sex-specific manner

This study aims at investigating whether environmental enrichment (EE) initiated in adolescence can alter chronic unpredictable stress (CUS)-associated changes in astroglial and synaptic plasticity markers in male and female rats. To this end, we studied possible alterations in hippocampal glial fibrillary acidic protein (GFAP) and synaptophysin (SYN) in CUS rats previously housed in EE. Wistar rats on postnatal day (PND) 23 were housed for 10 weeks in standard housing (SH) or enriched conditions. On PND 66, animals were exposed to CUS for 4 weeks. SYN and GFAP expressions were evaluated in CA1 and CA3 subfields and dentate gyrus (DG). CUS reduced the expression of SYN in all hippocampal areas, whereas lower GFAP expression was evident only in CA1 and CA3. The reduced expression of SYN in DG and CA3 was evident to male SH/CUS rats, whereas the reduced GFAP expression in CA1 and CA3 was limited to SH/CUS females. EE housing increased the hippocampal expression of both markers and protected against CUS-associated decreases. Our findings indicate that the decreases in the expression of SYN and GFAP following CUS are region and sex-specific and underline the neuroprotective role of EE against these CUS-associated changes.

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Long-term activation of hippocampal glial cells and altered emotional behavior in male and female adult rats after different neonatal stressors

Early life stress increases the risk of developing psychiatric diseases in adulthood. Severe neonatal infections can also contribute to the development of affective illnesses. Stress and infections both trigger the immediate activation of the neuroimmune system. We compared the long-term effects of neonatal single or combined stress-immune challenges on emotional behavior and glial cell responses in the hippocampus. Male and female Sprague Dawley rats were randomly allocated across four conditions: (1) control + vehicle; (2) maternal separation (MS, 3 h/day on postnatal days [PN] 1-14) + vehicle; (3) control + lipopolysaccharide (LPS, 0.5. mg/kg, PN14); (4) MS + LPS. The rats' behaviors were analyzed from PN120 in males and from PN150 in diestrous females. LPS, but not MS, increased anxiety-like behavior in male rats; however, in females, it increased with both challenges. Depressive-like behavior increased after MS-but not LPS-in males and females. Combined stressors increased depressive-like behavior in both sexes. All stressors promoted microglial activation in CA3 and hilus in males and females. MS and LPS increased the astrocytic density within the male hilus, but LPS only increased it in CA3. MS prevented the rise in astrocytic density with LPS. In females, MS reduced the astrocytic population of the hilus and CA3 areas. Taken together, the behavioral and glial cell responses to early life challenges are sex-dependent and cell-type specific. This suggests a sexual dimorphism in the nature of the adverse event faced. These results have implications for understanding the emergence of psychiatric illnesses.

Expression of synaptophysin and BDNF in the medial prefrontal cortex following early life stress and neonatal hypoxia-ischemia

This study aims at investigating whether early stress interacts with brain injury due to neonatal hypoxia-ischemia (HI). To this end, we examined possible changes in synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) expression in the medial prefrontal cortex (mPFC) of maternally separated rats that were subsequently exposed to a HI episode. Rat pups (n = 11) were maternally separated during postnatal days 1 to 6 (3hr/day), while another group was left undisturbed (n = 11). On postnatal day 7, a subgroup (n = 12) from each postnatal manipulation was exposed to HI. Synaptophysin and BDNF expression was estimated in mPFC prelimbic and anterior cingulate subregions of the ipsilateral and contralateral to the occluded common carotid artery hemispheres. Maternally separated rats expressed significantly less BDNF and SYN in both hemispheres. Neonatal HI significantly reduced BDNF and SYN expression in the ipsilateral mPFC only and this reduction was not further altered by early stress. Our findings indicate the enduring negative effect of a short period of maternal separation on the expression of mPFC SYN and BDNF. They, also, reveal that the HI-associated decreases in these markers are limited to the ipsilateral mPFC and are not exacerbated by early stress. These decreases may have important functional implications given the role of prefrontal area in high-order cognition.

Systematic review and meta-analysis: effects of maternal separation on anxiety-like behavior in rodents

The mechanisms by which childhood maltreatment increases anxiety is unclear, but a propensity for increased defensive behavior in rodent models of early life stress (ELS) suggests that work in rodents may clarify important mechanistic details about this association. A key challenge in studying the effects of ELS on defensive behavior in rodents is the plethora of inconsistent results. This is particularly prominent with the maternal separation (MS) literature, one of the most commonly used ELS models in rodents. To address this issue we conducted a systematic review and meta-analysis, examining the effects of MS on exploratory-defensive behavior in mice and rats using the open field test (OFT) and the elevated plus maze (EPM). This search yielded a total of 49 studies, 24 assessing the effect of MS on behavior in the EPM, 11 tested behavior in the OFT, and 14 studies provided data on both tasks. MS was associated with increased defensive behavior in rats (EPM: Hedge's g = -0.48, p = 0.02; OFT: Hedge's g = -0.33, p = 0.05), effect sizes that are consistent with the anxiogenic effect of early adversity reported in humans. In contrast, MS did not alter exploratory behavior in mice (EPM: Hedge's g = -0.04, p = 0.75; OFT: Hedge's g = -0.03, p = 0.8). There was a considerable amount of heterogeneity between studies likely related to the lack of standardization of the MS protocol. Together, these findings suggest important differences in the ability of MS to alter circuits that regulate defensive behaviors in mice and rats.

Treadmill running attenuates neonatal hypoxia induced adult depressive symptoms and promoted hippocampal neural stem cell differentiation via modulating AMPK-mediated mitochondrial functions

Neonatal hypoxia can induce the persisting brain dysfunctions and subsequently result in the behavioral abnormalities in adulthood. Improving mitochondrial functions were suggested as the effective strategy for brain functional recovery. In this study, we tested the effects of physical exercise, a well-established way benefits mitochondrion, for its functions to prevent hypoxia induced adult behavioral dysfunctions and the underlying molecular mechanism. Mice was induced with hypoxia and treadmill running were then administrated until the adulthood. The treadmill running resulted in the improved behavioral performance in depressive and anxiety tests together with the enhancement of hippocampal neurogenesis. We then detected treadmill running restored the mitochondrial morphology in adult neural stem cells (NSCs) as well as the ATP production in hippocampal tissue. In addition, activity of AMPK, which playing key roles in regulating mitochondrial functions, was also elevated by treadmill running. Blockage of AMPK with selective inhibitor compound C prohibited effects of treadmill running in attenuating neonatal hypoxia induced neurogenic impairment and antidepressant behavioral deficits in adulthood. In conclusion, treadmill running could prevent neonatal hypoxia induced adult antidepressant dysfunctions and neurogenic dampening via AMPK-mediated mitochondrial regulation.

Anxiety-like behaviour assessments of adolescent rats after repeated maternal separation during early life

Maternal separation (MS) plays a central role in developing physiology and psychology during the individual ontogeny process. MS is used to research the neurobiological mechanisms of mental disorders and early life stress. In this study, we investigated the effects of repeated MS and early handling (EH) on locomotor activity in an open-field test, a light–dark box test and an elevated plus-maze test of adolescent rats. The results showed that MS reduced locomotor activities in the open-field test, and increased anxiety-like behaviours in the light–dark box test and the elevated plus-maze test in adolescent rats. These tests indicated that early life stress caused by MS might induce anxiety-like behaviours during adolescence. However, compared with the control group, both the MS and EH groups showed conflicting anxiety levels. The results also suggested that females were more prone to showing anxiety-like behaviour compared with males when suffering from high-intensity stimulation. However, because of the low anxiety level associated with EH, the sex difference in behaviour was not significant. The present study provides novel insights into the effects of MS and EH on behaviour, which shows unique anxiety levels different in adolescent male and female rats.

Beneficial effects of environmental enrichment on behavior, stress reactivity and synaptophysin/BDNF expression in hippocampus following early life stress

Exposure to environmental enrichment can beneficially influence the behavior and enhance synaptic plasticity. The aim of the present study was to investigate the mediated effects of environmental enrichment on postnatal stress-associated impact with regard to behavior, stress reactivity as well as synaptic plasticity changes in the dorsal hippocampus. Wistar rat pups were submitted to a 3 h maternal separation (MS) protocol during postnatal days 1-21, while another group was left undisturbed. On postnatal day 23, a subgroup from each rearing condition (maternal separation, no-maternal separation) was housed in enriched environmental conditions until postnatal day 65 (6 weeks duration). At approximately three months of age, adult rats underwent behavioral testing to evaluate anxiety (Elevated Plus Maze), locomotion (Open Field Test), spatial learning and memory (Morris Water Maze) as well as non-spatial recognition memory (Novel Object Recognition Test). After completion of behavioral testing, blood samples were taken for evaluation of stress-induced plasma corticosterone using an enzyme-linked immunosorbent assay (ELISA), while immunofluorescence was applied to evaluate hippocampal BDNF and synaptophysin expression in dorsal hippocampus. We found that environmental enrichment protected against the effects of maternal separation as indicated by the lower anxiety levels and the reversal of spatial memory deficits compared to animals housed in standard conditions. These changes were associated with increased BDNF and synaptophysin expression in the hippocampus. Regarding the neuroendocrine response to stress, while exposure to an acute stressor potentiated corticosterone increases in maternally-separated rats, environmental enrichment of these rats prevented this effect. The current study aimed at investigating the compensatory role of enriched environment against the negative outcomes of adverse experiences early in life concurrently on emotional and cognitive behaviors, HPA function and neuroplasticity markers.

Chronic administration of parecoxib exerts anxiolytic-like and memory enhancing effects and modulates synaptophysin expression in mice

BACKGROUND

Previous studies have shown that cyclooxygenase-2, a key enzyme that converts arachidonic acid to prostaglandins, is involved in anxiety and cognitive processes, but few studies have investigated the effects of chronic administration of cyclooxygenase-2 inhibitors on anxiety, learning and memory under normal physiological conditions. The aim of the study was to investigate the effects of chronic administration of parecoxib, a cyclooxygenase-2 inhibitor, on anxiety behavior and memory performance under normal physiological conditions and to explore the possible neural mechanism underlying parecoxib-mediated effects.

METHODS

Adult male ICR mice were randomly divided into four groups: the control group and three parecoxib groups. Mice received normal saline or parecoxib (2.5, 5.0 or 10 mg/kg) intraperitoneal injection once a day for 21 days, respectively. Elevated plus-maze, novel object recognition and Y maze tests were conducted on day 23, 24 and 26, respectively. Four additional groups that received same drug treatment were used to measure synaptophysin protein levels by western blot and prostaglandin E2 (PGE2) levels by ELISA in the amygdala and hippocampus on day 26.

RESULTS

Chronic parecoxib exerted an anxiolytic-like effect in the plus-maze test test, and enhanced memory performance in the novel object recognition and Y maze tests. Western blot analysis showed that chronic parecoxib down-regulated synaptophysin levels in the amygdala and up-regulated synaptophysin levels in the hippocampus. ELISA assay showed that chronic parecoxib inhibited PGE2 in the hippocampus but not amygdala.

CONCLUSIONS

Chronic parecoxib exerts anxiolytic-like and memory enhancing effects, which might be mediated through differential modulation of synaptophysin and PGE2 in the amygdala and hippocampus.