Prednisolone increases neural reactivity to negative socio-emotional stimuli in healthy young men

Psycho-Behavioural Changes in Dogs Treated with Corticosteroids: A Clinical Behaviour Perspective

Simple Summary

Corticosteroids hormones are central to stress responses and, along with other hormones and neurotransmitters, contribute to the onset of physiological and behavioural changes aimed at helping the animal cope with anticipated demand. Both the human and animal literature suggest that exposure to systemic exogenous corticosteroid treatments can be associated with negative emotional states. In this paper, the potential behavioural effects of exogenous corticosteroid treatment on dogs and other species are discussed to show why consideration should be given to this matter when prescribing these drugs.

Abstract

Arousal and distress are often important factors in problematic behaviours, and endogenous corticosteroids are important mediators in the associated stress responses. Exogenous corticosteroid treatments have been reported to change behaviour in human patients and laboratory animals, with similar changes also noted in pet dogs. These behaviours not only potentially adversely impact the welfare of the dogs, but also the quality of life of their owners. Indeed, corticosteroids can bias sensitivity towards aversion in dogs. A decrease in behaviours associated with positive affective states, such as play and exploratory behaviours, together with an increase in aggression and barking have also been described in dogs. According to the available literature, human patients with pre-existing psychiatric disorders are more at risk of developing behavioural side effects due to corticosteroid treatments. It is reasonable to consider that the same may happen in dogs with pre-existing behavioural problems. In this paper, the possible behavioural side effects of exogenous corticosteroids are summarised to help inform and support veterinarians prescribing these drugs.

Structural covariance of amygdala subregions is associated with trait aggression and endogenous testosterone in healthy individuals

Many studies point toward volume reductions in the amygdala as a potential neurostructural marker for trait aggression. However, most of these findings stem from clinical samples, rendering unclear whether the findings generalize to non-clinical populations. Furthermore, the notion of neural networks suggests that interregional correlations in gray matter volume (i.e., structural covariance) can explain individual differences in aggressive behavior beyond local univariate associations. Here, we tested whether structural covariance between amygdala subregions and the rest of the brain is associated with self-reported aggression in a large sample of healthy young students (n = 263; 49% women). Salivary testosterone concentrations were measured for a subset of n = 40 male and n = 36 female subjects, allowing us to investigate the influence of endogenous testosterone on structural covariance. Aggressive individuals showed enhanced covariance between left superficial amygdala (SFA) and left dorsal anterior insula (dAI), but lower covariance between right laterobasal amygdala (LBA) and right dorsolateral prefrontal cortex (dlPFC). These structural patterns overlap with functional networks involved in the genesis and regulation of aggressive behavior, respectively. With increasing endogenous testosterone, we observed stronger structural covariance between right centromedial amygdala (CMA) and right medial prefrontal cortex in men and between left CMA and bilateral orbitofrontal cortex in women. These results speak for structural covariance of amygdala subregions as a robust correlate of trait aggression in healthy individuals. Moreover, regions that showed structural covariance with the amygdala modulated by either testosterone or aggression did not overlap, suggesting a complex role of testosterone in human social behavior beyond facilitating aggressiveness.

Glucocorticoids, metabolism and brain activity

The review integrates different experimental approaches including biochemistry, c-Fos expression, microdialysis (glutamate, GABA, noradrenaline and serotonin), electrophysiology and fMRI to better understand the effect of elevated level of glucocorticoids on the brain activity and metabolism. The available data indicate that glucocorticoids alter the dynamics of neuronal activity leading to context-specific changes including both excitation and inhibition and these effects are expected to support the task-related responses. Glucocorticoids also lead to diversification of available sources of energy due to elevated levels of glucose, lactate, pyruvate, mannose and hydroxybutyrate (ketone bodies), which can be used to fuel brain, and facilitate storage and utilization of brain carbohydrate reserves formed by glycogen. However, the mismatch between carbohydrate supply and utilization that is most likely to occur in situations not requiring energy-consuming activities lead to metabolic stress due to elevated brain levels of glucose. Excessive doses of glucocorticoids also impair the production of energy (ATP) and mitochondrial oxidation. Therefore, glucocorticoids have both adaptive and maladaptive effects consistently with the concept of allostatic load and overload.

Associations between brain activity and endogenous and exogenous cortisol - A systematic review

To arrive at a coherent understanding of the relation between glucocorticoids and the human brain, we systematically reviewed the literature for studies examining the associations between endogenous or exogenous cortisol and human brain function. Higher levels of endogenous cortisol during psychological stress were related to increased activity in the middle temporal gyrus and perigenual anterior cingulate cortex (ACC), decreased activity in the ventromedial prefrontal cortex, and altered function (i.e., mixed findings, increased or decreased) in the amygdala, hippocampus and inferior frontal gyrus. Moreover, endogenous cortisol response to psychological stress was related to increased activity in the inferior temporal gyrus and altered function in the amygdala during emotional tasks that followed psychological stress. Exogenous cortisol administration was related to increased activity in the postcentral gyrus, superior frontal gyrus and ACC, and altered function in the amygdala and hippocampus during conditioning, emotional and reward-processing tasks after cortisol administration. These findings were in line with those from animal studies on amygdala activity during and after stress.

Emotional Stability Interacts with Cortisol Levels Before fMRI on Brain Processing of Fearful Faces

Functional-Magnetic-Imaging (fMRI) is widely adopted to investigate neurophysiological correlates of emotion processing (EP). However, studies have reported that scanning procedures in neuroimaging protocols may increase or cause anxiety and psychological distress related with the scanning, thus inducing peripheral cortisol release. These phenomena may in turn impact on brain EP. Additionally, previous findings have indicated that inter-individual differences in stress-response intensity are mediated by levels of Emotional Stability (ES), a personality trait that has been associated with brain activity during EP, especially in amygdala and prefrontal cortex (PFC). The aim of this study was to investigate the interaction between indices of stress related to anticipation of fMRI scanning and levels of ES on amygdala and PFC activity during EP. With this aim, 55 healthy volunteers were characterized for trait ES. Furthermore, salivary cortisol levels at baseline and soon before fMRI scanning were measured as an index of stress related to scanning anticipation. During fMRI, participants performed an explicit EP task. We found that variation in salivary cortisol (Δc) interacts with ES on left amygdala and PFC activity during EP. More in details, in the context of a higher ES, the greater the Δc, the lower the activity in left amygdala and PFC. In the context of lower ES, the opposite Δc-brain activity relationship was found. Our results suggest that the stressful potential of fMRI interacts with personality traits in modulating brain activity during EP. These findings should be taken into account when interpreting neuroimaging studies especially exploring brain physiology during EP.

From words to action: Implicit attention to antisocial semantic cues predicts aggression and amygdala reactivity to angry faces in healthy young women

Implicit measures of aggressiveness are able to circumvent response biases that plague self-reports, but it is unclear how they link to neural activation during aggressive interactions and to aggression-related endocrine function. Here, we tested whether an implicit attentional bias toward antisocial semantic information was associated with endogenous testosterone (T) and cortisol (C) levels, as well as with aggressive behavior and amygdala reactivity to angry faces in a separate competitive paradigm. On Day one, participants (39 healthy young women) completed an emotional word Stroop task in which they had to indicate the font color of antisocial, prosocial, or neutral words. On Day two, we measured subjects' brain activity during a competitive reaction time task in which the female opponent displayed angry or neutral facial expressions at the start of each trial and provoked participants with increasingly strong sound blasts. T and C were measured in saliva during a regular weekday as well as before and after scanning. We previously showed that aggression was associated with enhanced amygdala reactivity to angry faces in this sample. The present analyses revealed that subjects were slower to identify the font color of antisocial relative to neutral words, and that this attentional bias predicted higher aggression. T and C were uncorrelated with Stroop scores. Crucially, the relationship between implicit attention to antisocial words and aggression was mediated by amygdala reactivity to angry faces. Our data indicate that a tendency to dwell on implicit hostile cues reflects enhanced responsivity to overt anger displays.

Glucocorticoid Administration Improves Aberrant Fear-Processing Networks in Spider Phobia

Glucocorticoids reduce phobic fear in patients with anxiety disorders. Previous studies have shown that fear-related activation of the amygdala can be mediated through the visual cortical pathway, which includes the fusiform gyrus, or through other pathways. However, it is not clear which of the pathways that activate the amygdala is responsible for the pathophysiology of a specific phobia and how glucocorticoid treatment alleviates fear processing in these neural networks. We recorded the brain activity with functional magnetic resonance imaging in patients with spider phobia, who received either 20 mg of cortisol or a placebo while viewing pictures of spiders. We also tested healthy participants who did not receive any medication during the same task. We performed dynamic causal modelling (DCM), a connectivity analysis, to examine the effects of cortisol on the networks involved in processing fear and to examine if there was an association between these networks and the symptoms of the phobia. Cortisol administration suppressed the phobic stimuli-related amygdala activity to levels comparable to the healthy participants and reduced subjective phobic fear. The DCM analysis revealed that cortisol administration suppressed the aberrant inputs into the amygdala that did not originate from the visual cortical pathway, but rather from a fast subcortical pathway mediated by the pulvinar nucleus, and suppressed the interactions between the amygdala and fusiform gyrus. This network changes were distinguishable from healthy participants and considered the residual changes under cortisol administration. We also found that the strengths of the aberrant inputs into the amygdala were positively correlated with the severity of spider phobia. This study demonstrates that patients with spider phobia show an aberrant functional connectivity of the amygdala when they are exposed to phobia-related stimuli and that cortisol administration can alleviate this fear-specific neural connectivity.