Role of the medial prefrontal cortex in coping and resilience

Internal gating and somatization disorders: proposing a yet un-described neural system

Medically unexplained symptoms (MUS) are a major medical burden and our current understanding of the pathophysiological process leading to their development remains minimal. While research has strongly linked chronic stress to the development of MUS the exact mechanisms and the reason for the many variations in the resultant symptomatology remain unclear. In this paper we advance the hypothesis that an internal (visceral) sensory gating system must exist akin to the much better studied external sensory gating system. The hypothesis is based on the observations that under normal conditions sensations of internal organs do not reach consciousness (i.e., filtered or gated out on a subconscious or preattentive level). As visceral sensations are usually perceived only when there is a pathological process affecting the organ, then failure of this internal gating system leading to the sensations arriving to consciousness must be interpreted by the brain to indicate pathology in this organ. If the hypothesis proves to be true and such a system does exist, the implications are many and significant including developing methods for assessing the system and possibly correcting it.

Exercise, stress resistance, and central serotonergic systems

Voluntary exercise reduces the incidence of stress-related psychiatric disorders in humans and prevents serotonin-dependent behavioral consequences of stress in rodents. Evidence reviewed herein is consistent with the hypothesis that exercise increases stress resistance by producing neuroplasticity at multiple sites of the central serotonergic system, which all help to limit the behavioral impact of acute increases in serotonin during stressor exposure.

The neurobiology of the stress-resistant brain

The 2010 Neurobiology of Stress Workshop brought together scientists from all over the world to share and discuss their results from studies examining the consequences of acute, repeated, and chronic stressor exposure on health and disease. Session IV entitled "The neurobiology of the stress-resistant brain" explored how we can intervene to promote stress resistance and stress resilience. Four scientists, who explore this topic from unique and convergent perspectives, presented their experimental results derived from studies in rat (Fleshner and Maier), non-human primates (Lyons), and human (Raskind). Summaries of each presentation, supporting publications, and overall take-home messages from the session are presented.

A unified framework for inhibitory control

Inhibiting unwanted thoughts, actions and emotions figures centrally in daily life, and the prefrontal cortex (PFC) is widely viewed as a source of this inhibitory control. We argue that the function of the PFC is best understood in terms of representing and actively maintaining abstract information, such as goals, which produces two types of inhibitory effects on other brain regions. Inhibition of some subcortical regions takes a directed global form, with prefrontal regions providing contextual information relevant to when to inhibit all processing in a region. Inhibition within neocortical (and some subcortical) regions takes an indirect competitive form, with prefrontal regions providing excitation of goal-relevant options. These distinctions are crucial for understanding the mechanisms of inhibition and how they can be impaired or improved.

Distinct behavioral consequences of stress models of depression in the elevated T-maze

Animals exposed to inescapable stress develop behavioral consequences that are similar to symptoms of depression. Therefore, most of the animal models of depression are based on animal exposure to such stressors. The stress-induced behavioral consequences induced by pre-exposure to shock in the learned helplessness model of depression have been proposed to be a consequence of excessive activation of fear/anxiety related structures which would lead to inhibitory avoidance and impaired escape performance. However, this hypothesis has not yet been investigated in a test that is able to generate these different defense strategies in a same rat, such as the elevated T-maze (ETM). Therefore, the objective of the present study was to test the effects of footshock pre-exposure (inescapable-IS or escapable-ES) on both inhibitory avoidance and escape responses of rats submitted to the ETM 24 h later. Moreover, since it is not known whether these effects would be a common feature to other inescapable stressors used as animal models of depression, we have also investigated the behavior of rats previously exposed to forced swimming or restraint. All stressed groups displayed anxiogenic-like behavior when compared to control groups (non-stressed), evidenced by facilitated acquisition of inhibitory avoidance in the ETM. However, only rats exposed to IS showed impaired escape performance. These results support the hypothesis that the facilitated inhibitory avoidance is a common behavioral consequence of distinct stressful stimuli. However, the impaired escape response is likely to be particularly involved in the mediation of the helpless behavior observed in rats pre-exposed to IS. The neurobiological mechanisms involved in these responses are discussed in the manuscript.

The mesoaccumbens dopamine in coping with stress

Mesoaccumbens dopamine (DA) is involved in the stress response. Although neural mechanisms involved in stress are of paramount importance for both clinical and preclinical research, the results of studies on the stress response by mesoaccumbens DA have received little attention. Therefore, we aimed to review these results and propose a role for mesoaccumbens DA in coping with stress. The data reviewed support the view that fluctuations of tonic levels characterize the mesoaccumbens DA stress response. Stress-induced increase of tonic DA levels in nucleus accumbens (NAc) supports expression of responses aimed at removing and avoiding the stressor through activation of DA D2 receptors, whereas inhibition of DA is associated with cessation of active defensive responses. In novel unescapable/uncontrollable stressful conditions tonic levels of DA in NAc show an initial increase followed by a decrease below pre-stress levels that lasts as long as the stressful situation. This biphasic response fits with the dynamics of the primary and secondary appraisal of a stressor that cannot be removed, escaped or controlled by the organism. In fact, NAc DA fluctuations are controlled by the medial pre-frontal cortex, which is involved in stress appraisal. We propose that enhanced mesoaccumbens DA supports expression of active coping strategies against an event appraised as a stressor and that inhibition of DA is required for passive coping with stressful situations appraised as unescapable/uncontrollable.