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.

Prenatal and adult androgen activities in alcohol dependence

OBJECTIVE

Alcohol dependence is more prevalent in men than in women. The evidence for how prenatal and adult androgens influence alcohol dependence is limited. We investigated the effects of prenatal and adult androgen activity on alcohol dependence. Moreover, we studied how the behaviours of pregnant women affect their children's prenatal androgen load.

METHOD

We quantified prenatal androgen markers (e.g., second-to-fourth finger length ratio [2D : 4D]) and blood androgens in 200 early-abstinent alcohol-dependent in-patients and 240 controls (2013-2015, including a 12-month follow-up). We also surveyed 134 women during pregnancy (2005-2007) and measured the 2D : 4D of their children (2013-2016).

RESULTS

The prenatal androgen loads were higher in the male alcohol-dependent patients compared to the controls (lower 2D : 4D, P = 0.004) and correlated positively with the patients' liver transaminase activities (P < 0.001) and alcohol withdrawal severity (P = 0.019). Higher prenatal androgen loads and increasing androgen levels during withdrawal predicted earlier and more frequent 12-month hospital readmission in alcohol-dependent patients (P < 0.005). Moreover, stress levels (P = 0.002), alcohol (P = 0.010) and tobacco consumption (P = 0.017), and lifetime stressors (P = 0.019) of women during pregnancy related positively to their children's prenatal androgen loads (lower 2D : 4D).

CONCLUSION

Androgen activities in alcohol-dependent patients and behaviours of pregnant women represent novel preventive and therapeutic targets of alcohol dependence.

αCaMKII controls the establishment of cocaine's reinforcing effects in mice and humans

Although addiction develops in a considerable number of regular cocaine users, molecular risk factors for cocaine dependence are still unknown. It was proposed that establishing drug use and memory formation might share molecular and anatomical pathways. Alpha-Ca(2+)/calmodulin-dependent protein kinase-II (αCaMKII) is a key mediator of learning and memory also involved in drug-related plasticity. The autophosphorylation of αCaMKII was shown to accelerate learning. Thus, we investigated the role of αCaMKII autophosphorylation in the time course of establishing cocaine use-related behavior in mice. We found that αCaMKII autophosphorylation-deficient αCaMKII(T286A) mice show delayed establishment of conditioned place preference, but no changes in acute behavioral activation, sensitization or conditioned hyperlocomotion to cocaine (20 mg kg(-1), intraperitoneal). In vivo microdialysis revealed that αCaMKII(T286A) mice have blunted dopamine (DA) and blocked serotonin (5-HT) responses in the nucleus accumbens (NAcc) and prefrontal cortex after acute cocaine administration (20 mg kg(-1), intraperitoneal), whereas noradrenaline responses were preserved. Under cocaine, the attenuated DA and 5-HT activation in αCaMKII(T286A) mice was followed by impaired c-Fos activation in the NAcc. To translate the rodent findings to human conditions, several CAMK2A gene polymorphisms were tested regarding their risk for a fast establishment of cocaine dependence in two independent samples of regular cocaine users from Brazil (n=688) and Switzerland (n=141). A meta-analysis across both samples confirmed that CAMK2A rs3776823 TT-allele carriers display a faster transition to severe cocaine use than C-allele carriers. Together, these data suggest that αCaMKII controls the speed for the establishment of cocaine's reinforcing effects.

Role of medial prefrontal, entorhinal, and occipital 5-HT in cocaine-induced place preference and hyperlocomotion: evidence for multiple dissociations

RATIONALE

Application of cocaine or exposure to cocaine-related stimuli induces widespread activation of the cortex in neuroimaging studies with human subjects. In accordance to these findings, it was reported in previous microdialysis experiments that cocaine increased serotonin (5-HT) and dopamine in various cortical brain areas. The present series of studies set out to investigate the functional role of the observed increases in 5-HT in the medial prefrontal cortex (mPFC), the entorhinal cortex (EC), and the occipital cortex (OccC) in the mediation of cocaine-induced conditioned place preference (CPP) and hyperactivity.

MATERIALS AND METHODS

To reduce 5-HTergic neurotransmission in circumscribed brain areas, bilateral local infusions of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), were made into the mPFC, EC, or OccC. Two weeks following surgery, cocaine-induced (10 mg/kg; i.p.) CPP was measured in an unbiased design.

RESULTS

The 90% depletion of 5-HT in the mPFC significantly attenuated the preference for the cocaine-associated environment and the hyperlocomotor response to cocaine. A 61% depletion of 5-HT in the EC reduced conditioned place preference without modulation of hyperactivity, while a 78% 5-HT depletion of the OccC cortex had no effect on cocaine-induced CPP and hyperactivity. No lesion affected general activity, habituation learning, or visual stimulation-induced behavioral activation.

CONCLUSION

These results indicate an important role of cortical 5-HT in the mediation of cocaine-induced CPP and specify the region-dependent contribution of a neurochemical response to cocaine-mediated behavior.

Visual sensory-motor gating by serotonin activation in the medial prefrontal and occipital, but not in the rhinal, cortices in rats

A behavioral reaction to sensory stimulation is a basic mechanism which is pivotal to many complex behavioral responses. In previous studies we found that visual stimulation induces a selective serotonergic and dopaminergic activation in the occipital (OccC), but not temporal (TempC) cortex in freely moving rats. In a behavioral study in rats we demonstrate now that visual stimulation (0, 8, 22, 82, 155 or 440 lux) activates behavioral activity in an intensity-dependent manner. Behavior activating visual stimulation with 82 lux, but not 22 lux or 82 dB white noise, increased extracellular serotonin (5-HT), but not dopamine (DA), in the medial prefrontal cortex (mPFC) in freely moving animals measured by in vivo microdialysis. There was no effect on 5-HT or DA in the entorhinal and perirhinal cortex. Visual stimulation with 82 lux increased extracellular 5-HT in the mPFC and OccC also in anesthetized animals, but had no effect in the TempC. Auditory stimulation reduced 5-HT in the TempC, but had no effect in the mPFC or OccC. Neither visual nor auditory stimulation had a significant effect on DA in all three cortical areas. We conclude that visual stimulation induces behavioral activation by increasing 5-HT activity in the mPFC and OccC.

Dissociating effects of cocaine and d-amphetamine on dopamine and serotonin in the perirhinal, entorhinal, and prefrontal cortex of freely moving rats

RATIONALE

Neuroimaging studies with humans showed widespread activation of the cortex in response to psychostimulant drugs. However, the neurochemical nature of these brain activities is not characterized.

OBJECTIVE

The aim of the present study was to investigate the effects of cocaine and d-amphetamine on dopamine (DA) and serotonin (5-HT) in cortical areas of the hippocampal network in comparison to the prefrontal cortex (PFC).

MATERIALS AND METHODS

We conducted in vivo microdialysis experiments in behaving rats measuring DA and 5-HT in the perirhinal cortex (PRC), entorhinal cortex (EC), and PFC, after application of cocaine (0, 5, 10, 20 mg/kg; i.p.) or d-amphetamine (0, 0.5, 1.0, 2.5 mg/kg; i.p.).

RESULTS

Cocaine and d-amphetamine dose-dependently increased DA and 5-HT levels in the PRC, EC, and PFC. A predominant DA response to d-amphetamine was only found in the PFC, but not in the PRC and EC. Cocaine increased DA and 5-HT to an equal extent in the PFC and PRC but induced a predominant 5-HT response in the EC. When comparing the neurochemical responses between the drugs at an equal level of behavioral activation, cocaine was more potent than d-amphetamine in increasing 5-HT in the PFC, while no differences were found in the PRC or EC or in the DA responses in all three cortical areas.

CONCLUSIONS

We conclude that cocaine and d-amphetamine increase DA and 5-HT levels in PRC and EC largely to the same extent as in the PFC.

Cocaine-induced ???active immobility??? and its modulation by the serotonin1A receptor

'Active immobility' (AI) is an independent behaviour that can be characterized by behavioural immobility, an increased muscular rigidity and the sustaining of an unusual posture. In previous studies with cocaine we observed, concomitant with hyperlocomotion and increased rearing activity, an increase in AI in well-habituated animals, which may constitute another 'positive' acute effect of cocaine on behaviour. The contribution of the serotonergic (5-HT) system to AI is well established. However, little information exists about the contribution of particular 5-HT-receptor subtypes. In order to examine a possible role of the 5-HT1A receptor on this effect of cocaine, we systematically re-analysed four previous experiments in well-habituated animals and one in little-habituated animals, focusing on the acute behavioural effects of cocaine on AI. We found that, in well-habituated animals, cocaine at a medium dose (10 mg/kg, i.p.) induces AI behaviour, which, however, does not correlate with cocaine effects on locomotion, rearing or grooming behaviour. However, there was no effect of cocaine (1, 5 or 15 mg/kg, i.p.) on AI in little-habituated animals. The 5-HT1A-receptor antagonist, WAY 100635 [N-[2-(4-2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide trihydrochloride] (0.4 mg/kg, i.p.), potentiated cocaine-induced AI in well-habituated animals, while the 5-HT1A-receptor agonist, 8-OH-DPAT (0.2 mg/kg, i.p.), attenuated it. The local application of 8-OH-DPAT [8-hydroxy-2-(di-n-propylamino)tetralin] into the nucleus accumbens (0, 1, 10 micromol/l) or hippocampus (0, 0.1, 1, 10 micromol/l) modulated cocaine-induced AI in a complex way. These results showed that cocaine induces AI at a medium dose in well-habituated but not in little-habituated animals. The cocaine-induced AI in well-habituated animals can be potentiated by systemic 5-HT1A-receptor antagonism and attenuated by 5-HT1A-receptor agonism. Two experiments with local activation of postsynaptic 5-HT1A receptors revealed that both nucleus accumbens and hippocampal 5-HT1A-receptor populations are involved in the expression of cocaine-induced AI.

Nucleus accumbens serotonin1A receptors control cocaine-induced hyperactivity but not local serotonin increase: an in vivo microdialysis study

The nucleus accumbens (Nac) is an important structure for cocaine-induced hyperactivity and receives a dense serotonergic (5-HT) innervation. Previous studies showed that a systemic activation of 5-HT(1A) receptors potentiates cocaine-induced hyperlocomotion, but attenuates the cocaine-induced 5-HT increase in the Nac. In order to address the role of Nac 5-HT(1A) receptors in the control of cocaine-induced and spontaneous behavioural activity and local 5-HT release, we used in vivo microdialysis in freely moving rats. The 5-HT(1A)-receptor agonist, 8-OH-DPAT (0, 1 and 10 microM), was applied locally into the Nac by reverse dialysis followed by a cocaine (10 mg/kg) or saline i.p. injection. The Nac 5-HT(1A)-receptor activation potentiated cocaine-induced hyperlocomotion, but attenuated rearing behaviour dose-dependently. Parallel to that, the cocaine-induced increase in Nac 5-HT dialysate level was unaffected, as were the decreases in 5-HIAA and DOPAC dialysate levels after cocaine. In saline treated rats, the local application of 8-OH-DPAT into the Nac affected neither spontaneous behavioural activity nor 5-HT, 5-HIAA or DOPAC dialysate levels in the Nac. These data suggest that Nac 5-HT(1A) receptors exert a bi-directional control of cocaine-induced hyperactivity, while not affecting spontaneous behaviour. Furthermore, accumbal 5-HT(1A) receptors do not appear to be directly involved in the acute effects of cocaine on 5-HT, 5-HIAA or DOPAC levels in the Nac.

Serotonin1A-receptor agonism attenuates the cocaine-induced increase in serotonin levels in the hippocampus and nucleus accumbens but potentiates hyperlocomotion: an in vivo microdialysis study

The hippocampus and the nucleus accumbens (Nac) are important structures for the modulation of spontaneous locomotor activity. Both structures receive a serotonergic (5-HT) innervation. We have previously reported that the 5-HT(1A)-receptor antagonist WAY 100635 blocked cocaine-induced hyperactivity, while potentiating cocaine-induced 5-HT increases in the hippocampus and the Nac. In order to further investigate the relationship between extracellular 5-HT concentration and cocaine-induced behaviour, we used in vivo microdialysis to measure the effects of the 5-HT(1A)-receptor agonist 8-OH-DPAT on cocaine-induced changes in the extracellular 5-HT concentration in the hippocampus and the Nac and on behavioural activity. Following a pilot pretest in which we determined the lowest effective dose of 8-OH-DPAT for potentiating cocaine-induced hyperlocomotion, four groups of rats were given one of the following drug treatments: 8-OH-DPAT (0.2 mg/kg) and cocaine (10 mg/kg), saline and cocaine (10 mg/kg), 8-OH-DPAT (0.2 mg/kg) and saline, or saline and saline. The injections were administered i.p. and spaced 30 min apart. We found that the 5-HT(1A)-receptor agonist 8-OH-DPAT attenuated the cocaine-induced increases in 5-HT in the hippocampus and the Nac, but potentiated cocaine-induced hyperlocomotion. 5-HT metabolite measurements revealed a complex role for the 5-HT(1A)-receptor in the broad spectrum of cocaine's neurochemical effects. Altogether, these observations support an important role of the 5-HT(1A)-receptor in the hippocampus and Nac in the modulation of cocaine stimulant effects.

Auditory noise can prevent increased extracellular acetylcholine levels in the hippocampus in response to aversive stimulation

The intent of this study was to investigate neurochemical and behavioural effects of aversive stimulation and the impact of auditory background noise. Using in vivo microdialysis, hippocampal acetylcholine was extracted and subjected to HPLC analysis while male Wistar rats were exposed to aversive stimulation similar to that used in conventional procedures for aversive conditioning. Three groups of animals were used. Animals in the first group were exposed to a single tone/footshock pairing followed by a tone alone 2 h later. Animals in the second group served as controls and were only exposed to the tone without shock. A third group was exposed to the same tone/shock pairing and tone as the first group while being exposed to constant background noise during the whole experiment. The results showed, that the tone/shock combination led to pronounced behavioral and cholinergic activation. In contrast, exposure to background noise prevented the increase in hippocampal ACh levels to tone/shock stimulation. The unconditioned behavioural response, however, was not prevented suggesting that hippocampal ACh is not a necessary correlate of behavioural activation or arousal. A second experiment intended to investigate the effects of background noise in a shuttle box avoidance learning paradigm where rats were trained to avoid an aversive footshock, which was signalled by a tone. There, one group of rats was exposed to background noise during avoidance learning, and the other group was not exposed to noise. Whereas both groups learned to avoid the shock to some degree over training, the noise exposed animals did not show improvement in escape performance over the course of training, indicating that the noise hindered development of an adaptive response to the shock. In summary, our data indicate that background noise can prevent increased extracellular hippocampal ACh levels in response to an aversive stimulus, and can also lead to deficits in learning to escape from shock.

High versus low reactivity to a novel environment: behavioural, pharmacological and neurochemical assessments

Based on their rearing response to a novel open field, male Wistar rats were divided into two sub-groups with either high or low behavioural activity (high rearings, versus low rearings). These sub-groups were repeatedly exposed to the same open field and tested for behavioural habituation. Since we previously found neurochemical evidence for different cholinergic reactivities in such high rearing and low rearing rats, their behavioural responses to the muscarinic antagonist scopolamine (0.5 mg/kg) were also investigated in the open field. Additionally, they were exposed to the elevated plus-maze to test for possible differences in measures of anxiety. After behavioural testing, tissue concentrations of biogenic amines were determined in the ventral striatum (nucleus accumbens, olfactory tubercle), frontal cortex, striatum, hippocampus and amygdala. The results show that the higher rearing responses of high rearing rats in the novel open field were paralleled by higher locomotor activity. These behavioural differences between groups decreased with repeated open field exposure, an effect which was largely due to between-session habituation in high rearing rats. Thereby, high rearing rats approached the lower levels of low rearing rats, in which locomotor activity and rearings did not habituate between testing. Nevertheless, habituation was also observed in low rearing rats, especially in the measure of thigmotactic scanning, since the levels of scanning declined both between and within test sessions. The anticholinergic challenge with scopolamine induced a general pattern of behavioural activation. Furthermore, scopolamine partly reinstated the behavioural differences between high and low rearing rats that had been observed in the novel open field, since high rearing rats showed more rearing behaviour than low rearing rats under scopolamine. In contrast to the open field, there were no significant differences between high and low rearing rats in the plus-maze. The neurochemical analysis revealed, among others, higher dopamine levels in the ventral striatum of high rearing rats together with lower serotonin levels in the medial frontal cortex. The current findings thus indicate that high and low rearing rats not only differ in their behavioural response to a novel environment, but also in their patterns of behavioural habituation, and with respect to behaviour induced by an anti-cholinergic challenge. These differential behavioural profiles of high and low rearing animals are discussed with respect to the role of dopaminergic mechanisms in the forebrain, and the potential impact of cholinergic mechanisms.

Relationship between anxiety and serotonin in the ventral striatum

Rats were tested in an elevated plus-maze on two consecutive days. Based on the percentage of time spent in the open arms on the 1st day, they were divided into two subgroups with either low or high anxiety levels. A post-mortem neurochemical analysis showed that animals with high anxiety had lower ventral striatal tissue levels of 5-HT. No such differences were found for 5-HT in other brain areas or in dopamine and norepinephrine levels. The ventral striatal 5-HT levels correlated with plus-maze behavior on the 2nd but not 1st day. These data suggest that individual differences in ventral striatal 5-HT interact with plus-maze behavior, which may help to explain why serotonergic drugs can have inconsistent effects in this paradigm.