Duration of Social Isolation Affects Production of Nitric Oxide in the Rat Brain

Resocialization mitigates depressive behaviors induced by social isolation stress in mice: Attenuation of hippocampal neuroinflammation and nitrite level

BACKGROUND AND AIM

Social isolation stress (SIS) is a stressor known to trigger depressive behaviors. Psychiatric disorders are associated with neurobiological changes, such as neuroinflammation and an increase in nitric oxide (NO) signaling. Despite the well-established detrimental effects of SIS and the involvement of neuroinflammation and NO in depression, potential management strategies, especially resocialization, remain insufficiently explored. Our aim was to elucidate the effects of resocialization on depressive behaviors in socially isolated mice, with a focus on the possible involvement of neuroinflammation and nitrite in the hippocampus (HIP).

METHODS

We utilized 24 Naval Medical Research Institute male mice, maintained under both social and isolation conditions (SC and IC). After the isolation period, the mice were divided into two groups of eight, including the SIS group and a resocialized group. The SC group was kept without exposure to isolation stress. We conducted the open-field test, forced swimming test, and splash test to evaluate depressive behaviors. Additionally, nitrite levels, as well as the gene expression of interleukin (IL)-1β, tumor necrosis factor (TNF), and toll-like receptor 4 (TLR4) in the HIP, were measured.

RESULTS

The study found that resocialization significantly reduces depressive behaviors in SIS mice. The results suggest that the antidepressive effects of resocialization may be partially due to the modulation of the neuroinflammatory response and nitrite levels in the HIP. This is supported by the observed decrease in hippocampal gene expression of IL-1β, TLR4, and TNF, along with a reduction in nitrite levels following resocialization.

CONCLUSION

These insights could pave the way for new management strategies for depression, emphasizing the potential benefits of social interactions.

Role of Acorus calamus in preventing depression, anxiety, and oxidative stress in long-term socially isolated rats

Background and Aim

Social isolation stress (SIS) and individual housing have been shown to cause abnormal cognitive insufficiencies, altered anxiety levels, and signs of psychiatric diseases. Acorus calamus (AC), commonly known as Sweet Flag, has been widely used in India to treat neurological, metabolic, and respiratory disorders, indicating its potential therapeutic value. This study aimed to determine the antidepressant and antioxidative effects of AC on rats subjected to long-term, social isolation-induced stress.

Materials and Methods

This study involved 2-month-old male rats (24) weighing approximately 180-200 g bred in-house. The rats were divided into four groups (n = 6): Group 1 received saline, Group 2 received SIS, Group 3 received only 50 mg/kg AC, and Group 4 received 50 mg/kg AC and SIS for 6 weeks. After this, behavioral, biochemical, and neuronal assays were conducted.

Results

Behavioral experiments showed significantly higher activity levels (p < 0.001) in AC-treated rats than in the SIS group. In addition, rats subjected to SIS with AC treatment exhibited enhanced total antioxidants, superoxide dismutase, and neuronal assays compared to rats subjected to SIS alone.

Conclusion

Acorus calamus treatment improved the antidepressant and antioxidant potential against SIS in rat brain tissue. Moreover, we proved that AC can effectively reverse the neurotoxicity induced by SIS in animal models. As we battle against the coronavirus disease 2019 pandemic and social isolation, AC could be considered a supplementary treatment to alleviate depressive-like symptoms in our present-day lifestyle.

Nine-month-long Social Isolation Changes the Levels of Monoamines in the Brain Structures of Rats: A Comparative Study of Neurochemistry and Behavior

Social isolation (SI) is chronic psycho-emotional stress for humans and other socially living species. There are few comparative studies that have measured monoamine levels in brain structures in male and female rats subjected to SI. Existing data is highly controversial. In our recent study, we investigated behavioral effects of SI prolonged up to 9 months on a rather large sample of 69 male and female Wistar rats. In the present study, we measured the levels of monoamines-norepinephrine (NE), dopamine (DA), 5-hydroxytryptamine (5-HT), and DA and 5-HT metabolites-in the brain structures of 40 rats from the same sample. The single-housed rats of both sexes showed hyperactivity and reduced reactivity to novelty in the Open Field test, and impaired passive avoidance learning. Regardless of their sex, by the time of sacrifice, the single-housed rats weighed less and had lower pain sensitivity and decreased anxiety compared with group-housed animals. SI decreased NE levels in the hippocampus and increased them in the striatum. SI induced functional activation of the DA-ergic system in the frontal cortex and hypothalamus, with increased DA and 3-methoxytyramine levels. SI-related changes were found in the 5-HT-ergic system: 5-HT levels increased in the frontal cortex and striatum, while 5-hydroxyindoleacetic acid only increased in the frontal cortex. We believe that SI prolonged for multiple months could be a valuable model for comparative analysis of the behavioral alterations and the underlying molecular processes in dynamics of adaptation to chronic psychosocial stress in male and female rats in relation to age-dependent changes.

Absence of a significant interaction of two common NOS1 and 5-HTT polymorphisms on sensorimotor gating in humans

The neurotransmitter serotonin has been critically implicated in the pathogenesis of several mental disorders. The serotonin transporter (5-HTT) is a key regulator of serotonergic neurotransmission and its genetic variability is associated with increased risk of psychopathology. One well known polymorphic locus in the 5-HTT gene affecting its expression is a tandem repeat in the promoter region (5-HTTLPR). It has been reported that 5-HTT is functionally coupled with the neuronal nitric oxide synthase (NOS1 or nNOS), an enzyme catalyzing the production of nitric oxide (NO). We have previously demonstrated that a tandem repeat polymorphism in the promoter of NOS1 exon 1f (Ex1f-VNTR) is associated with sensorimotor gating, a marker of inhibitory processing and a well established endophenotype of several neuropsychiatric disorders. Here we investigated the combined genetic effects of NOS1 Ex1f-VNTR and 5-HTTLPR on sensorimotor gating, measured by prepulse inhibition (PPI) of the acoustic startle reflex, in 164 healthy adults. We found no evidence for the interaction between NOS1 Ex1f-VNTR and 5-HTTLPR on PPI. PPI was associated with NOS1 Ex1f-VNTR, but not 5-HTTLPR. Our data suggest that while NOS1 plays a role in sensorimotor gating, the nitrergic pathway of gating regulation does not involve the action of 5-HTT.