Behavioural brain research
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Resilience is an active process that involves a discrete set of neural substrates and cellular mechanisms and enables individuals to avoid some of the negative consequences of extreme stress. We have previously shown that dominant individuals show less stress-induced changes in behavior compared to subordinates using a conditioned defeat model in male Syrian hamsters (Mesocricetus auratus). To rule out pre-existing differences between dominants and subordinates, we examined whether 14 days of dominance experience is required to reduce the conditioned defeat response and whether the development of conditioned defeat resistance correlates with defeat-induced neural activation in select brain regions. ⋯ We found that 14-day dominants showed a decreased conditioned defeat response compared to 14-day subordinates and controls, while 1-day and 7-day dominants did not differ from their subordinate counterparts. Also, the duration of dominance relationship was associated with distinct patterns of defeat-induced neural activation such that only 14-day dominants showed elevated c-Fos immunoreactivity in the ventral medial prefrontal cortex, medial amygdala, and lateral portions of the ventral medial hypothalamus. Our data suggest that resistance to social stress develops during the maintenance of dominance relationships and is associated with experience-dependent neural plasticity in select brain regions.
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Environmental factors influence a variety of health-related outcomes. In general, being raised in an environment possessing social, sensory, and motor enrichment reduces the rewarding effects of various drugs, thus protecting against abuse vulnerability. However, in the case of methamphetamine (METH), which acts at the vesicular monoamine transporter 2 (VMAT2) to enhance dopamine release from the cytosol, previous evidence suggests that METH reward may not be altered by environmental enrichment. ⋯ However, cue-induced reinstatement was reduced by environmental enrichment. Together, these results suggest that environmental enrichment does not alter VMAT2 function involved in METH reward. However, the enrichment-induced decrease in cue-induced reinstatement indicates that enrichment may have a beneficial effect against relapse following a period of extinction via a neural mechanism other than striatal VMAT2 function.
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In clinical populations, prevalence rates for a number of anxiety disorders differ between males and females and gonadal hormones are thought to contribute to these differences. While these hormones have been shown to modulate the anxiolytic effects of the benzodiazepine agonist diazepam in some models, findings are inconsistent. Here, we tested for sex differences in response to anxiogenic stimuli following a 30-min diazepam (1.0mg/kg) pre-treatment in male and female rats showing high (HAn) and low (LAn) anxiety-like behavior on the elevated plus maze. ⋯ In the CeA, males displayed an increased number of PV-IR neurons compared to females, with no differences found between LAn and HAn. Further, trait differences were evident in the CA2 region of the hippocampus, regardless of sex. Taken together, these data suggest that gonadal hormones and trait anxiety may influence the sensitivity to the anti-anxiety effects of diazepam and these differences may be due in part to the distribution of GABA-containing interneurons.
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There are several reports that cognitive impairment is observed in stress related disorders and chronic stress impairs learning and memory. However, very few studies have looked into the possible ways of preventing this stress-induced deficit. This research study was conducted to evaluate the effects of quercetin, a natural flavonoid, with strong antioxidant and free radical scavenger properties, on chronic stress induced learning and memory deficits and oxidative stress in hippocampus. ⋯ Quercetin treatment caused a significant decrease in the hippocampus MDA levels and improves SOD and GPx activities in stressed animals. Finally, quercetin significantly decreased plasma corticosterone levels in stressed animals. Based on results of this study, chronic stress has detrimental effects on learning and memory and quercetin treatment can prevent from oxidative stress and impairment of learning and memory induced by chronic stress.
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Neonatal alcohol exposure in rodents causes dramatic neurodegenerative effects throughout the developing nervous system, particularly in the striatum, acutely after exposure. These acute neurodegenerative effects are augmented in mice lacking adenylyl cyclases 1 and 8 (AC1/8) as neonatal mice with a genetic deletion of both AC isoforms (DKO) have increased vulnerability to ethanol-induced striatal neurotoxicity compared to wild type (WT) controls. While neonatal ethanol exposure is known to negatively impact cognitive behaviors, such as executive functioning and working memory in adolescent and adult animals, the threshold of ethanol exposure required to impinge upon developmental behaviors in mice has not been extensively examined. ⋯ Locomotor stimulation was significantly increased in animals that received ethanol as neonates, peaking significantly in ethanol-treated DKO mice compared to ethanol-treated WT controls, while sedation duration following high-dose ethanol challenge was unaffected. These data indicate that the maturational parameters examined in the current study may not be sensitive enough to detect effects of a single ethanol exposure during the brain growth spurt period. Genetic deletion of AC1/8 reveals a role for these cylases in attenuating ethanol-induced behavioral effects in the neonatally-exposed adolescent.