Fluoxetine exerts subregion/layer specific effects on parvalbumin/GAD67 protein expression in the dorsal hippocampus of male rats showing social isolation-induced depressive-like behaviour

The effect of acute crocin on behavioral changes and BDNF expression level in socially isolated rats

Social isolation is a reliable method used for the induction of depression and psychiatric disorders in rodents. It has been suggested that social isolation can lead to hyperlocomotion, as a schizophrenic-like symptom in rodents. On the other hand, crocin (the major constituent of Crocus sativus) induces a wide-range of neuroprotective and mood enhancer effects. In the present study, we aimed to investigate the effect of acute crocin on social isolation-induced behavioral changes and BDNF expression in the hippocampus. Novelty-suppressed feeding test, open field test, marble burying test, hot plate, forced swim test, and the shuttle box were used to assess anxiety-like behavior, locomotor activity, obsessive-compulsive-like (OCD-like) behavior, pain threshold, depressive-like behavior, and passive avoidance memory, respectively. Real-time PCR was used to assess BDNF hippocampal expression level. The results showed that social isolation decreased anxiety- and depressive-like behavior, pain threshold, and BDNF expression, and induced OCD-like behavior and hyperlocomotion. Crocin dose-dependently restored the effect of social isolation on pain threshold, locomotor activity, depressive-like behavior, OCD-like behavior, and BDNF expression. Passive avoidance memory performance was also unaffected. In conclusion, we showed a hyperlocomotion profile and OCD-like behaviors, and a robust decrease in pain threshold in socially isolated rats. It can be suggested that social isolation from adolescence induces a "hyperlocomotion state" that affects all the behavioral functions of rats. Also, the function of BDNF can be related to a hyperlocomotion state and OCD-like symptom. It seems that BDNF expression level can be related to the therapeutic effect of crocin.

GABAergic and inflammatory changes in the frontal cortex following neonatal PCP plus isolation rearing, as a dual-hit neurodevelopmental model for schizophrenia

The pathogenesis of schizophrenia begins in early neurodevelopment and leads to excitatory-inhibitory imbalance. It is therefore essential that preclinical models used to understand disease, select drug targets and evaluate novel therapeutics encompass similar neurochemical deficits. One approach to improved preclinical modelling incorporates dual-hit neurodevelopmental insults, like neonatal administration of phencyclidine (PCP, to disrupt development of glutamatergic circuitry) then post-weaning isolation (Iso, to mimic adolescent social stress). We recently showed that male Lister-hooded rats exposed to PCP-Iso exhibit reduced hippocampal expression of the GABA interneuron marker calbindin. The current study expanded on this by investigating changes to additional populations of GABAergic interneurons in frontal cortical and hippocampal tissue from the same animals (by immunohistochemistry) as well as levels of GABA itself (via ELISA). Because inflammatory changes are also implicated in schizophrenia, we performed additional immunohistochemical evaluations of Iba-1 positive microglia as well as ELISA analysis of IL-6 in the same brain regions. Single-hit isolation-reared and dual-hit PCP-Iso rats both showed reduced parvalbumin immunoreactivity in the prelimbic/infralimbic region of the frontal cortex. However, this was more widespread in PCP-Iso, extending to the medial/ventral and lateral/dorsolateral orbitofrontal cortices. Loss of GABAergic markers was accompanied by increased microglial activation in the medial/ventral orbitofrontal cortices of PCP-Iso, together with frontal cortical IL-6 elevations not seen following single-hit isolation rearing. These findings enhance the face validity of PCP-Iso, and we advocate the use of this preclinical model for future evaluation of novel therapeutics-especially those designed to normalise excitatory-inhibitory imbalance or reduce neuroinflammation.

Olanzapine Effects on Parvalbumin/GAD67 Cell Numbers in Layers/Subregions of Dorsal Hippocampus of Chronically Socially Isolated Rats

Depression is linked to changes in GABAergic inhibitory neurons, especially parvalbumin (PV) interneurons, which are susceptible to redox dysregulation. Olanzapine (Olz) is an atypical antipsychotic whose mode of action remains unclear. We determined the effect of Olz on PV-positive (+) and glutamate decarboxylase 67 (GAD67) + cell numbers in the layers of dorsal hippocampus (dHIPP) cornu ammonis (CA1-CA3) and dentate gyrus (DG) subregions in rats exposed to chronic social isolation (CSIS), which is an animal model of depression. Antioxidative enzymes and proinflammatory cytokine levels were also examined. CSIS decreased the PV+ cell numbers in the Stratum Oriens (SO) and Stratum Pyramidale (SP) of dCA1 and dDG. It increased interleukin-6 (IL-6), suppressor of cytokine signaling 3 (SOCS3), and copper-zinc superoxide dismutase (CuZnSOD) levels, and it decreased catalase (CAT) protein levels. Olz in CSIS increased the number of GAD67+ cells in the SO and SP layers of dCA1 with no effect on PV+ cells. It reduced the PV+ and GAD67+ cell numbers in the Stratum Radiatum of dCA3 in CSIS. Olz antagonizes the CSIS-induced increase in CuZnSOD, CAT and SOCS3 protein levels with no effect on IL-6. Data suggest that the protective Olz effects in CSIS may be mediated by altering the number of PV+ and GAD67+ cells in dHIPP subregional layers.

Sucrose preference test: A systematic review of protocols for the assessment of anhedonia in rodents

Anhedonia is described as a decreased ability to experience rewarding and enjoyable activities, a core symptom of major depressive disorder. The sucrose preference test (SPT) is a widely used and reliable behavioural test to assess anhedonia in rodents, based on a two-bottle choice paradigm. To date, different protocols are in use, inducing variability between researchers and hampering comparisons between studies. We performed a systematic review of the SPT protocols used in 2021 to identify the parameters in which they differ and their potential impact. We searched a total of four databases (PubMed, Scopus, Web of Science and Science Direct), from 1st January 2021 to 31st December 2021, and screened a total of 1066 articles. After screening by title and abstract, a total of 415 articles were included in this review. We extracted and analysed the different procedures used, the type of sweet solution and the habituation, deprivation, and testing protocols. The overall quality of the studies was considered very good, however, SPT protocols were extremely variable between studies with a total of 65 different habituation protocols and 104 combinations of food/water deprivation and preference testing duration. As the SPT is one of the most used tests to assess anhedonia in rodents, this work raises awareness of the great variability in SPT protocols being currently used. Furthermore, we call for standardization in the protocol used, and overall improvement of data reporting of methodologies and results, to increase the consistency between studies and allow a better comparison of results between different labs.

Intermittent Theta Burst Stimulation Improves Motor and Behavioral Dysfunction through Modulation of NMDA Receptor Subunit Composition in Experimental Model of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder characterized by the progressive degeneration of the dopaminergic system, leading to a variety of motor and nonmotor symptoms. The currently available symptomatic therapy loses efficacy over time, indicating the need for new therapeutic approaches. Repetitive transcranial magnetic stimulation (rTMS) has emerged as one of the potential candidates for PD therapy. Intermittent theta burst stimulation (iTBS), an excitatory protocol of rTMS, has been shown to be beneficial in several animal models of neurodegeneration, including PD. The aim of this study was to investigate the effects of prolonged iTBS on motor performance and behavior and the possible association with changes in the NMDAR subunit composition in the 6-hydroxydopamine (6-OHDA)-induced experimental model of PD. Two-month-old male Wistar rats were divided into four groups: controls, 6-OHDA rats, 6-OHDA + iTBS protocol (two times/day/three weeks) and the sham group. The therapeutic effect of iTBS was evaluated by examining motor coordination, balance, spontaneous forelimb use, exploratory behavior, anxiety-like, depressive/anhedonic-like behavior and short-term memory, histopathological changes and changes at the molecular level. We demonstrated the positive effects of iTBS at both motor and behavioral levels. In addition, the beneficial effects were reflected in reduced degeneration of dopaminergic neurons and a subsequent increase in the level of DA in the caudoputamen. Finally, iTBS altered protein expression and NMDAR subunit composition, suggesting a sustained effect. Applied early in the disease course, the iTBS protocol may be a promising candidate for early-stage PD therapy, affecting motor and nonmotor deficits.

Fluoxetine Enhances Synaptic Vesicle Trafficking and Energy Metabolism in the Hippocampus of Socially Isolated Rats

Chronic social isolation (CSIS)-induced alternation in synaptic and mitochondrial function of specific brain regions is associated with major depressive disorder (MDD). Despite the wide number of available medications, treating MDD remains an important challenge. Although fluoxetine (Flx) is the most frequently prescribed antidepressant, its mode of action is still unknown. To delineate affected molecular pathways of depressive-like behavior and identify potential targets upon Flx treatment, we performed a comparative proteomic analysis of hippocampal purified synaptic terminals (synaptosomes) of rats exposed to six weeks of CSIS, an animal model of depression, and/or followed by Flx treatment (lasting three weeks of six-week CSIS) to explore synaptic protein profile changes. Results showed that Flx in controls mainly induced decreased expression of proteins involved in energy metabolism and the redox system. CSIS led to increased expression of proteins that mainly participate in Ca²⁺/calmodulin-dependent protein kinase II (Camk2)-related neurotransmission, vesicle transport, and ubiquitination. Flx treatment of CSIS rats predominantly increased expression of proteins involved in synaptic vesicle trafficking (exocytosis and endocytosis), and energy metabolism (glycolytic and mitochondrial respiration). Overall, these Flx-regulated changes in synaptic and mitochondrial proteins of CSIS rats might be critical targets for new therapeutic development for the treatment of MDD.

Dramatic impacts on brain pathology, anxiety, and cognitive function in the knock-in APPNL-G-F mouse model of Alzheimer disease following long-term voluntary exercise

Background

An active lifestyle is associated with improved cognitive functions in aged people and may prevent or slow down the progression of various neurodegenerative diseases including Alzheimer’s disease (AD). To investigate these protective effects, male APP^NL-G-F mice were exposed to long-term voluntary exercise.

Methods

Three-month-old AD mice were housed in a cage supplemented with a running wheel for 9 months for long-term exercise. At the age of 12 months, behavioral tests were completed for all groups. After completing behavioral testing, their brains were assessed for amyloid pathology, microgliosis, and cholinergic cells.

Results

The results showed that APP^NL-G-F mice allowed to voluntarily exercise showed an improvement in cognitive functions. Furthermore, long-term exercise also improved anxiety in APP^NL-G-F mice as assessed by measuring thigmotaxis in the Morris water task. We also found reductions in amyloid load and microgliosis, and a preservation of cholinergic cells in the brain of APP^NL-G-F mice allowed to exercise in their home cages. These profound reductions in brain pathology associated with AD are likely responsible for the observed improvement of learning and memory functions following extensive and regular exercise.

Conclusion

These findings suggest the potential of physical exercise to mitigate the cognitive deficits in AD.

Environmental enrichment as a strategy: Attenuates the anxiety and memory impairment in social isolation stress

BACKGROUND

Social isolation (SI) early in life produces behavioral and cognitive abnormalities. On the contrary, environmental enrichment (EE) offers beneficial effects on brain plasticity and development. This study was designed to examine how EE affects memory functions, anxiety level, and the expression levels of memory/anxiety-related genes such as NR2A, NR2B, BDNF, and cFos in the hippocampus of socially isolated rats.

MATERIALS AND METHODS

Wistar albino male rats (n = 40) were separated into the five groups: Standard cage (SC), SI, EE, SI + SC, and SI + EE group. For each group, eight rats were housed, either grouped or isolated, in a standard or 3-week EE, respectively. Morris water maze test (MWMT) was used for measuring the learning and memory function. Elevated plus maze (EPM) and open field (OF) were used for the evaluation of anxiety behavior. Blood corticosterone level was evaluated by the ELISA method. The expression levels of genes were measured by the RT-PCR method.

RESULTS

Results showed that EE increased memory performance in the SI group (p < 0.05). SI caused anxiety while EE improved anxiety behavior (p < 0.05). There was no significant difference between the groups in the OF test. Corticosterone levels did not change between groups. BDNF expression level was downregulated in EE and SI + SC compared with the SC group (respectively; p = 0.012; p = 0.011). NR2A, NR2B, and cFos expression levels did not change between groups significantly.

CONCLUSIONS

SI impaired memory performance while EE has beneficial effects on memory in socially isolated rats. EE alone was insufficient to cause alterations in the memory performance. The therapeutic effects of EE became strengthened while applied together with stress protocol. Together with improving the effectiveness of memory function, EE has the potential to decrease anxiety behavior. EE seemed to be the reason for decreasing in BDNF.

Impact of stress on inhibitory neuronal circuits, our tribute to Bruce McEwen

This manuscript is dedicated to the memory of Bruce S. McEwen, to commemorate the impact he had on how we understand stress and neuronal plasticity, and the profound influence he exerted on our scientific careers. The focus of this review is the impact of stressors on inhibitory circuits, particularly those of the limbic system, but we also consider other regions affected by these adverse experiences. We revise the effects of acute and chronic stress during different stages of development and lifespan, taking into account the influence of the sex of the animals. We review first the influence of stress on the physiology of inhibitory neurons and on the expression of molecules related directly to GABAergic neurotransmission, and then focus on specific interneuron subpopulations, particularly on parvalbumin and somatostatin expressing cells. Then we analyze the effects of stress on molecules and structures related to the plasticity of inhibitory neurons: the polysialylated form of the neural cell adhesion molecule and perineuronal nets. Finally, we review the potential of antidepressants or environmental manipulations to revert the effects of stress on inhibitory circuits.