Colocalisation of c-Fos and glucocorticoid receptor as well as of 5-HT1A and glucocorticoid receptor immunoreactivity-expressing cells in the brain structures of low and high anxiety rats

Individual differences in inflammatory and oxidative mechanisms of stress-related mood disorders

Emotional stress leads to the development of peripheral disorders and is recognized as a modifiable risk factor for psychiatric disorders, particularly depression and anxiety. However, not all individuals develop the negative consequences of emotional stress due to different stress coping strategies and resilience to stressful stimuli. In this review, we discuss individual differences in coping styles and the potential mechanisms that contribute to individual vulnerability to stress, such as parameters of the immune system and oxidative state. Initial differences in inflammatory and oxidative processes determine resistance to stress and stress-related disorders via the alteration of neurotransmitter content in the brain and biological fluids. Differences in coping styles may serve as possible predictors of resistance to stress and stress-related disorders, even before stressful conditions. The investigation of natural variabilities in stress resilience may allow the development of new methods for preventive medicine and the personalized treatment of stress-related conditions.

Cananga odorata essential oil reverses the anxiety induced by 1-(3-chlorophenyl) piperazine through regulating the MAPK pathway and serotonin system in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cananga odorata essential oil, known as ylang-ylang essential oil (YYO), was commonly used in the aromatherapy for relaxation and mood adjusting use. In our previous study, YYO played anxiolytic effects on the mice in several behavioral tests that based on the instinctive responses to novel environments.

AIM OF THE STUDY

To investigate the effects and mechanisms of YYO reversing the anxiety induced by 5-HT2C receptor agonist 1-(3-chlorophenyl) piperazine (m-CPP).

MATERIALS AND METHODS

m-CPP was administrated to the male ICR mice to develop an anxiety model. The anxiolytic effect of YYO (0.1%, 1% and 10%, v/v) was evaluated in the elevated plus maze (EPM) test after odor exposure. Western blot was used to detect the phosphorylation levels of extracellular signal-regulated kinase 1/2 (ERK1/2) and cAMP response element-binding protein (CREB) and the expression of c-Fos in the prefrontal cortex (PFC) and hippocampus after the EPM test. Serotonin and its metabolite change in the brain were detected by liquid chromatogram with an electrochemical detector. The effect of YYO on the plasma corticosterone level was evaluated using enzyme-linked immunosorbent assay (ELISA) after the odor exposure.

RESULTS

The behavior analysis showed that m-CPP (2 mg/kg and 4 mg/kg) could induce anxiety behaviors in the mice while diazepam (2 mg/kg) reversed the anxiety behavior induced by m-CPP. YYO dose-dependently increased the time and number of entries in the open arms (p < 0.05) compared to the Tween 80 group. YYO reduced the phosphorylation levels of ERK1/2 (p < 0.05) in both PFC and hippocampus. Down-regulations of phosphor-CREB (p < 0.05) and c-Fos (p < 0.05) were only observed in the hippocampus. YYO also affected the brain serotonin metabolism and reduced the blood plasma corticosterone level of the m-CPP treated mice.

CONCLUSION

YYO odor exposure could reverse the anxiety behaviors generated by m-CPP. The anxiolytic effect of YYO was associated with the ERK1/2/CREB pathway in the hippocampus and relevant to the serotonin system.

Repeated Systemic Treatment with Rapamycin Affects Behavior and Amygdala Protein Expression in Rats

BACKGROUND

Clinical data indicate that therapy with small-molecule immunosuppressive drugs is frequently accompanied by an incidence rate of neuropsychiatric symptoms. In the current approach, we investigated in rats whether repeated administration of rapamycin, reflecting clinical conditions of patients undergoing therapy with this mammalian target of rapamycin inhibitor, precipitates changes in neurobehavioral functioning.

METHODS

Male adult Dark Agouti rats were daily treated with i.p. injections of rapamycin (1, 3 mg/kg) or vehicle for 8 days. On days 6 and 7, respectively, behavioral performance in the Elevated Plus-Maze and the Open-Field Test was evaluated. One day later, amygdala tissue and blood samples were taken to analyze protein expression ex vivo.

RESULTS

The results show that animals treated with rapamycin displayed alterations in Elevated Plus-Maze performance with more pronounced effects in the higher dose group. Besides, an increase in glucocorticoid receptor density in the amygdala was seen in both treatment groups even though p-p70 ribosomal S6 kinase alpha, a marker for mammalian target of rapamycin functioning, was not affected. Protein level of the neuronal activity marker c-Fos was again only elevated in the higher dose group. Importantly, effects occurred in the absence of acute peripheral neuroendocrine changes.

CONCLUSIONS

Our findings indicate that anxiety-related behavior following rapamycin treatment was not directly attributed to mTOR-dependent mechanisms or stress but rather due to hyperexcitability of the amygdala together with glucocorticoid receptor-regulated mechanism(s) in this brain region. Together, the present results support the contention that subchronic treatment with rapamycin may induce neurobehavioral alterations in healthy, naive subjects. We here provide novel insights in central effects of systemic rapamycin in otherwise healthy subjects but also raise the question whether therapy with this drug may have detrimental effects on patients' neuropsychological functioning during immune therapy.

Stress-induced hippocampus Npas4 mRNA expression relates to specific psychophysiological patterns of stress response

Neuronal Per-Arnt-Sim (PAS) domain protein 4 (Npas4) is a key protein that intervenes in GABA synapse scaling and neurotrophicity enhancing. Since GABA and neurotrophicity are implicated in stress response and Npas4-deficient rodents exhibit behavioral alterations, an investigation was designed in rats to verify whether stress-induced spontaneous hippocampus Npas4 mRNA expression would be associated with specific patterns of stress response. The rats were exposed to one of three stressor levels: no stress (CTL, n = 15), exposure to a footshock apparatus (Sham, S, n = 40) and footshock (F, n = 80). After stress exposure the S and F rats were tested in an activity cage, and subsequently in an elevated plus maze (EPM), just prior to the sacrifice. Using cluster analysis, the animals already assigned to a stress level were also distributed into 2 subgroups depending on their Npas4 mRNA levels. The low (L) and high (H) Npas4 expression subgroups were identified in the S and F groups, the CTL group being independent of the Npas4 levels. The Npas4 effect was studied through the interaction between stress (S and F) and Npas4 level (L and H). The biological stress response was similar in H and L rats, except blood corticosterone that was slightly lower in the H rats. The H rats were more active in the actimetry cage and presented higher levels of exploration in the EPM. They also exhibited higher hippocampus activation, as assessed by the c-fos, Egr1 and Arc mRNA levels. Therefore high Npas4 expression favors stress management.

Midazolam treatment before re-exposure to contextual fear reduces freezing behavior and amygdala activity differentially in high- and low-anxiety rats

The aim of this study was to examine the effects of benzodiazepine (midazolam) administration on rat conditioned fear responses and on local brain activity (c-Fos and CRF expressions) of low- (LR) and high- (HR)anxiety rats after the first and second contextual fear test sessions. The animals were divided into LR and HR groups based on the duration of their conditioned freezing response in the first contextual fear test. The fear-re-conditioned LR and HR animals (28 days later) had increased freezing durations compared with those durations during the first conditioned fear test. These behavioral effects were accompanied by increased c-Fos expression in the medial amygdala (MeA), the basolateral amygdala (BLA), and the paraventricular hypothalamic nuclei and elevated CRF expression in the MeA. All these behavioral and immunochemical effects of fear re-conditioning were stronger in the LR group compared with the effects in the HR group. Moreover, in the LR rats, the re-conditioning led to decreased CRF expression in the primary motor cortex (M1) and to increased CRF expression in the BLA. The pretreatment of rats with midazolam before the second exposure to the aversive context significantly attenuated the conditioned fear response, lowered the serum corticosterone concentration, decreased c-Fos and CRF expressions in the MeA and in the BLA, and increased CRF complex density in M1 area only in the LR group. These studies have demonstrated that LR rats are more sensitive to re-exposure to fear stimuli and that midazolam pretreatment was associated with modified brain activity in the amygdala and in the prefrontal cortex in this group of animals. The current data may facilitate a better understanding of the neurobiological mechanisms responsible for individual differences in the psychopathological processes accompanying some anxiety disorders characterized by stronger reactivity to re-exposure to stressful challenges, e.g., posttraumatic stress disorder.

The effect of chronic administration of corticosterone on anxiety- and depression-like behavior and the expression of GABA-A receptor alpha-2 subunits in brain structures of low- and high-anxiety rats

The aim of this study was to examine changes in rat emotional behavior and determine differences in the expression of GABA-A receptor alpha-2 subunits in brain structures of low- (LR) and high-anxiety (HR) rats after the repeated corticosterone administration. The animals were divided into LR and HR groups based on the duration of their conditioned freezing in a contextual fear test. Repeated daily administration of corticosterone (20 mg/kg) for 21 days decreased activity in a forced swim test, reduced body weight and decreased prefrontal cortex corticosterone concentration in both the LR and HR groups. These effects of corticosterone administration were stronger in the HR group in comparison with the appropriate control group, and compared to LR treated and LR control animals. Moreover, in the HR group, chronic corticosterone administration increased anxiety-like behavior in the open field and elevated plus maze tests. The behavioral effects in HR rats were accompanied by a decrease in alpha-2 subunit density in the medial prefrontal cortex (prelimbic cortex and frontal association cortex) and by an increase in the expression of alpha-2 subunits in the basolateral amygdala. These studies have shown that HR rats are more susceptible to anxiogenic and depressive effects of chronic corticosterone administration, which are associated with modification of GABA-A receptor function in the medial prefrontal cortex and basolateral amygdala. The current data may help to better understand the neurobiological mechanisms responsible for individual differences in changes in mood and emotions induced by repeated administration of high doses of glucocorticoids or by elevated levels of these hormones associated with chronic stress or affective pathology.