Elsevier

Biological Psychiatry

Volume 66, Issue 4, 15 August 2009, Pages 384-392
Biological Psychiatry

Archival Report
Involvement of NOX2 in the Development of Behavioral and Pathologic Alterations in Isolated Rats

https://doi.org/10.1016/j.biopsych.2009.04.033Get rights and content

Background

Social stress leads to oxidative stress in the central nervous system, contributing to the development of mental disorders. Loss of parvalbumin in interneurons is an important feature of these diseases. We studied the role of the superoxide-producing nicotinamide adenosine dinucleotide phosphate (NADPH) oxidase 2 (NOX2) in rats exposed to social isolation.

Methods

Male rats were kept for 7 weeks in group or in social isolation (n = 6–10 per group). Behavioral tests, immunohistochemistry, and analysis of NOX2 expression were performed at the end of social isolation. Apocynin was given in the drinking water (5 mg/kg/day).

Results

NOX2 was below detection level in the brains of control animals, whereas it was highly expressed in isolated rats, particularly in nucleus accumbens and prefrontal cortex. Indirect markers of oxidative stress (oxidized nucleic acid 8-hydroxy-2′-deoxyguanosine, redox-sensitive transcription factor c-fos, and hypoxia-inducible factor-1α) were increased after social isolation in brain areas with high NOX2 expression. An increase in immunoreactive microglia suggested that oxidative stress could be in part due to NOX2 activation in microglia. In response to social isolation, rats showed increased locomotor activity, decreased discrimination, signs of oxidative stress in neurons, and loss of parvalbumin-immunoreactivity. Treatment of isolated rats with the antioxidant/NOX inhibitor apocynin prevented the behavioral and histopathological alterations induced by social isolation.

Conclusions

Our data suggest that NOX2-derived oxidative stress is involved in loss of parvalbumin immunoreactivity and development of behavioral alterations after social isolation. These results provide a molecular mechanism for the coupling between social stress and brain oxidative stress, as well as potential new therapeutic avenues.

Section snippets

Animals

An equal number of adult male and female Wistar rats (Harlan, S. Pietro al Natisone, Udine, Italy) were used to obtain litters. A total number of 17 dams provided offspring for inclusion in the study. All animals were housed at a constant room temperature (22° ± 3°C) and relative humidity (55% ± 5%) under a 12-hour light/dark cycle (lights on from 7:00 am to 7:00 pm). Food and water were freely available. All efforts were made to minimize the number of animals used and their suffering in

Induction of NOX2 Expression in Rat Brain After Social Isolation

We performed reverse transcriptase (RT)-PCR to assess the effect of social isolation on NOX2 gene expression in specific areas of rat brain: amygdala (AMY), hippocampus (HIPP), nucleus accumbens (NACC), prefrontal cortex (PFC), and striatum (STR.). Whereas NOX2 mRNA was below detection levels in the five selected brain areas of control rats (n = 5), NOX2 transcripts in isolated rats (n = 5) were detected in four of these five brain regions (AMY, HIPP, NACC, and PFC, but not in STR). The

Discussion

In this study, we investigated the relationship among social-isolation-induced brain alterations, NOX2, and oxidative stress. We demonstrate that social isolation of young rats leads to an upregulation of NOX2 and all subunits (p47phox, p22phox, p67phox, p40phox) required for the activation of the enzyme. The upregulation of NOX2 is accompanied by signs of brain oxidative stress, increased microglia immunostaining, decrease of parvalbumin-immunoreactivity in neurons and behavioral alterations.

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    Authors SSo, SSc, LT, and K-HK contributed equally to this work.

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