Hippocampal cytogenesis and spatial learning in senile rats exposed to chronic variable stress: effects of previous early life exposure to mild stress

Visual EMDR stimulation mitigates acute varied stress effects on morphology of hippocampal neurons in male Wistar rats

Introduction

Stress is a pervasive health concern known to induce physiological changes, particularly impacting the vulnerable hippocampus and the morphological integrity of its main residing cells, the hippocampal neurons. Eye Movement Desensitization and Reprocessing (EMDR), initially developed to alleviate emotional distress, has emerged as a potential therapeutic/preventive intervention for other stress-related disorders. This study aimed to investigate the impact of Acute Variable Stress (AVS) on hippocampal neurons and the potential protective effects of EMDR.

Methods

Rats were exposed to diverse stressors for 7 days, followed by dendritic morphology assessment of hippocampal neurons using Golgi-Cox staining.

Results

AVS resulted in significant dendritic atrophy, evidenced by reduced dendritic branches and length. In contrast, rats receiving EMDR treatment alongside stress exposure exhibited preserved dendritic morphology comparable to controls, suggesting EMDR's protective role against stressinduced dendritic remodeling.

Conclusions

These findings highlight the potential of EMDR as a neuroprotective intervention in mitigating stress-related hippocampal alterations.

Early-life stress does not alter spatial memory performance, hippocampal neurogenesis, neuroinflammation, or telomere length in 20-month-old male mice

Early-life stress (ES) increases the risk for psychopathology and cognitive decline later in life. Because the neurobiological substrates affected by ES (i.e., cognition, neuroplasticity, and neuroinflammation) are also altered in aging, we set out to investigate if and how ES in the first week of life affects these domains at an advanced age, and how ES modulates the aging trajectory per se. We subjected C57BL/6j mice to an established ES mouse model from postnatal days 2–9. Mice underwent behavioral testing at 19 months of age and were sacrificed at 20 months to investigate their physiology, hippocampal neuroplasticity, neuroinflammation, and telomere length. ES mice, as a group, did not perform differently from controls in the open field or Morris water maze (MWM). Hippocampal neurogenesis and synaptic marker gene expression were not different in ES mice at this age. While we find aging-associated alterations to neuroinflammatory gene expression and telomere length, these were unaffected by ES. When integrating the current data with those from our previously reported 4- and 10-month-old cohorts, we conclude that ES leads to a ‘premature’ shift in the aging trajectory, consisting of early changes that do not further worsen at the advanced age of 20 months. This could be explained e.g. by a ‘floor’ effect in ES-induced impairments, and/or age-induced impairments in control mice. Future studies should help understand how exactly ES affects the overall aging trajectory.

•

Early-life stress (ES) exposure does not worsen water maze learning in aged male mice.

•

ES does not affect brain plasticity markers at 20 months of age.

•

Hippocampal telomere length is reduced by aging but unaffected by ES.

•

ES leads to a premature aging trajectory that does not worsen with aging.

Altered D2 receptor and transcription factor EB expression in offspring of aggressive male rats, along with having depressive and anxiety-like behaviors

MATERIALS AND METHODS

In this study we have evaluated the behavioral mood variations, and expression of DR-D2 and TFEB genes in the amygdala and PFC of aggressive male rats' offspring.

RESULTS

Anxiety and depression-like behaviors were observed, but intra-ventricle injection of DR-D2 antagonist (Sulpiride) has shown to be efficient in reducing negative behavioral changes in offspring. Furthermore, DR-D2 gene expression was increased in the amygdala and PFC of aggressive male rats' offspring, which the injection of Sulpiride decreased it significantly. TFEB gene expression was also decreased in the amygdala and PFC of aggressive male rats' offspring, but the blockade of DR-D2 had no effect on it.

CONCLUSIONS

The current data suggests the possible influence of dopaminergic receptors D2 and TFEB genes on the behavioral changes which is modified by having an aggressive father.

Norepinephrine in the dentate gyrus is involved in spatial learning and memory alteration induced by chronic restraint stress in aged rats

The role of norepinephrine of the hippocampal dentate gyrus in spatial learning and memory alteration induced by chronic restraint stress (CRS, 3 h/day, 6 weeks) was investigated in aged rats. Spatial learning and memory were assessed by the Morris water maze (MWM), and the extracellular concentration of norepinephrine and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the dentate gyrus during MWM test in freely-moving rats. Next, the involvement of β-adrenoceptors in spatial learning and memory of CRS rats was examined by microinjection of its antagonist (propranolol) into the dentate gyrus. In addition, we observed the expression of brain-derived neurotrophic factor (BDNF) protein and activation of cAMP-response element binding protein (CREB) in the dentate gyrus. Compared with the control group, the basal level of norepinephrine, BDNF expression and CREB activation in the dentate gyrus were increased, and the spatial learning and memory abilities were enhanced in CRS rats. In the control group, the norepinephrine concentration and fEPSP amplitude in the dentate gyrus were increased on the second to fourth days of MWM test, and these responses were significantly enhanced in CRS rats. Furthermore, in CRS rats, propranolol significantly decreased the spatial learning and memory abilities, and attenuated the fEPSP response during MWM test, and the BDNF expression and CREB activation in the dentate gyrus. Our results suggest that norepinephrine activation of β-adrenoceptors in the hippocampal dentate gyrus is involved in spatial learning and memory enhancement induced by CRS in aged rats, in part via modulations of synaptic efficiency and CREB-BDNF signaling pathway.

Male rats exhibit higher pro-BDNF, c-Fos and dendritic tree changes after chronic acoustic stress

Prolonged or intense exposure to environmental noise (EN) has been associated with a number of changes in auditory organs as well as other brain structures. Notably, males and females have shown different susceptibilities to acoustic damage as well as different responses to environmental stressors. Rodent models have evidence of sex-specific changes in brain structures involved in noise and sound processing. As a common effect, experimental models have demonstrated that dendrite arborizations reconfigure in response to aversive conditions in several brain regions. Here, we examined the effect of chronic noise on dendritic reorganization and c-Fos expression patterns of both sexes. During 21 days male and female rats were exposed to a rats' audiogram-fitted adaptation of a noisy environment. Golgi-Cox and c-Fos staining were performed at auditory cortices (AC) and hippocampal regions. Sholl analysis and c-Fos counts were conducted for evidence of intersex differences. In addition, pro-BDNF serum levels were also measured. We found different patterns of c-Fos expression in hippocampus and AC. While in AC expression levels showed rapid and intense increases starting at 2 h, hippocampal areas showed slower rises that reached the highest levels at 21 days. Sholl analysis also evidenced regional differences in response to noise. Dendritic trees were reduced after 21 days in hippocampus but not in AC. Meanwhile, pro-BDNF levels augmented after EN exposure. In all analyzed variables, exposed males were the most affected. These findings suggest that noise may exert differential effects on male and female brains and that males could be more vulnerable to the chronic effects of noise.

Early life stress by repeated maternal separation induces long-term neuroinflammatory response in glial cells of male rats

Childhood maltreatment and neglect lead to a wide range of mental disorders highlighted by hormone and immune alterations in neglected children. This social-health challenge has led to the creation of early stress models such as maternal separation (MS) in rodents. We performed a MS model (4 h per day, 21 days; n = 16 MS and n = 16 control), and then measured three parameters in adult male rat brains, in order to look for long-term effects of early life stress. We used immunocytochemistry to mark glial fibrillary acidic protein (GFAP)-positive cells, which indicates changes in astroglia, and ionized calcium binding adaptor molecule 1 (Iba-1)-positive cells, which inform about reactive microglia. In order to study mRNA levels of some immune mediators, interleukin determination (interleukin-6, IL-6; tumor necrosis factor, TNFα) mRNAs were evaluated by real-time polymerase chain reaction (rt-PCR) in discrete brain regions. Measurements of numbers of GFAP-positive cells, and expression of Iba-1, IL-6 and TNFα mRNAs were performed in prefrontal cortex (PFC): cingulate cortex (CG), prelimbic cortex (PL) and infralimbic cortex (IL), striatal areas (dorsal striatum, STD; and nucleus accumbens, ACC), and dorsal hippocampus (HC: CA1, CA3 and dentate gyrus (DG)). We found that MS produces a dramatic and sustained decrease in the astroglial population in all the areas measured (from -25% in CA1 to -85.7% in ACC), whereas increased numbers of microglia were found, in more restricted regions: STD (72.6%), ACC (31%) and CA3 (33.3%) areas. Regarding mRNA measurements, we found increased IL-6 mRNA expression in HC (104.2%), and after MS.

Environmental noise exposure modifies astrocyte morphology in hippocampus of young male rats

Background:

Chronic exposure to noise induces changes on the central nervous system of exposed animals. Those changes affect not only the auditory system but also other structures indirectly related to audition. The hippocampus of young animals represents a potential target for these effects because of its essential role in individuals’ adaptation to environmental challenges.

Objective:

The aim of the present study was to evaluate hippocampus vulnerability, assessing astrocytic morphology in an experimental model of environmental noise (EN) applied to rats in pre-pubescent stage.

Materials and Methods:

Weaned Wistar male rats were subjected to EN adapted to the rats’ audiogram for 15 days, 24 h daily. Once completed, plasmatic corticosterone (CORT) concentration was quantified, and immunohistochemistry for glial fibrillary acidic protein was taken in hippocampal DG, CA3, and CA1 subareas. Immunopositive cells and astrocyte arborizations were counted and compared between groups.

Results:

The rats subjected to noise exhibited enlarged length of astrocytes arborizations in all hippocampal subareas. Those changes were accompanied by a marked rise in serum CORT levels.

Conclusions:

These findings confirm hippocampal vulnerability to EN and suggest that glial cells may play an important role in the adaptation of developing the participants to noise exposure.

The involvement of astrocytes in early-life adversity induced programming of the brain

Early‐life adversity (ELA) in the form of stress, inflammation, or malnutrition, can increase the risk of developing psychopathology or cognitive problems in adulthood. The neurobiological substrates underlying this process remain unclear. While neuronal dysfunction and microglial contribution have been studied in this context, only recently the role of astrocytes in early‐life programming of the brain has been appreciated. Astrocytes serve many basic roles for brain functioning (e.g., synaptogenesis, glutamate recycling), and are unique in their capacity of sensing and integrating environmental signals, as they are the first cells to encounter signals from the blood, including hormonal changes (e.g., glucocorticoids), immune signals, and nutritional information. Integration of these signals is especially important during early development, and therefore we propose that astrocytes contribute to ELA induced changes in the brain by sensing and integrating environmental signals and by modulating neuronal development and function. Studies in rodents have already shown that ELA can impact astrocytes on the short and long term, however, a critical review of these results is currently lacking. Here, we will discuss the developmental trajectory of astrocytes, their ability to integrate stress, immune, and nutritional signals from the early environment, and we will review how different types of early adversity impact astrocytes.

Social stress during adolescence activates long-term microglia inflammation insult in reward processing nuclei

The experience of social stress during adolescence is associated with higher vulnerability to drug use. Increases in the acquisition of cocaine self-administration, in the escalation of cocaine-seeking behavior, and in the conditioned rewarding effects of cocaine have been observed in rodents exposed to repeated social defeat (RSD). In addition, prolonged or severe stress induces a proinflammatory state with microglial activation and increased cytokine production. The aim of the present work was to describe the long-term effects induced by RSD during adolescence on the neuroinflammatory response and synaptic structure by evaluating different glial and neuronal markers. In addition to an increase in the conditioned rewarding effects of cocaine, our results showed that RSD in adolescence produced inflammatory reactivity in microglia that is prolonged into adulthood, affecting astrocytes and neurons of two reward-processing areas of the brain (the prelimbic cortex, and the nucleus accumbens core). Considered as a whole these results suggest that social stress experience modulates vulnerability to suffer a loss of glia-supporting functions and neuronal functional synaptic density due to drug consumption in later life.