Neurocircuit control of the hypothalamo-pituitary-adrenocortical axis during stress:

Neuroendocrine regulation of the stress response in adult zebrafish, Danio rerio

The main objectives of this study were to investigate the dynamics of the cortisol stress response and the underlying molecular regulation in adult zebrafish exposed to acute and long-term stressors that differed in nature, duration and relative intensity. Fish showed a very rapid and prolonged increase in trunk cortisol concentrations, starting at around 15min and returning to basal levels at around 2h following exposure to acute stressors. In addition, acute stress affected significantly brain mRNA expression levels of several genes (corticotropin-releasing factor, crf; pro-opiomelanocortin, pomc; glucocorticoid receptor, gr; MR/GR ratio; prolactin, prl; hypocretin/orexin, hcrt; brain-derived neurotrophic factor, bdnf; c-fos). Exposure of fish to unpredictable relatively low-grade environmental and husbandry stressors (SP-1) did not affect the overall behaviour of fish, as well as trunk cortisol concentrations. Fish exposed to relatively higher-grade long-term stressors (SP-2) showed elevated cortisol levels as well as significant changes in most of gene transcripts. In particular, fish exposed to SP-2 showed statistically significant upregulation in brain gr, mr, prl and hcrt compared to SP-1 and control individuals. The highest mean values of bdnf transcripts were found in SP-2 exposed zebrafish and the lowest in control fish, while an approximately 5 to 6-fold upregulation was observed in c-fos mean relative mRNA levels of long-term stress-exposed fish, regardless of stressor intensity, compared to control zebrafish. In conclusion, we developed realistic acute and unpredictable long-term stress protocols, based on husbandry and environmental stressors and physical, chemical, mechanical and social stimuli that fish may experience either in nature or under intensive rearing conditions.

Pain and natural disaster

The treatment for pain in emergency medicine is a matter of increasing interest. Available data indicate that in both normal conditions and during major-emergencies, the majority of healthcare providers are culturally and professionally unprepared to adequately treat acute pain conditions. In case of natural disasters, opioid drugs are often unavailable. Moreover, no guidelines or validated protocols provide adequate indications for the treatment for pain in case of massive emergencies. Training of the medical and nursing staff, in both formal and continuing, or on-the-job education is needed to adequately face a devastating emergency. Unfortunately, there is an inadequate level of training among healthcare professionals, even in highly seismic areas, and the source of aid is frequently limited, especially in the immediate aftermath of a disaster to those already present at the scene. Pain inadequately treated may modify the characteristics of the pain itself. Pain is no longer considered just a symptom, but itself becomes an autonomous pathology heavily influencing the social life and psycho-social aspects of a person. In the disastrous situation following an earthquake, an inadequate treatment of pain was the major violation of the psycho-physical integrity of individuals and a severe violation of their rights, as human beings and patients.

Contribution of the vagus nerve and lamina terminalis to brain activation induced by refeeding

Following refeeding, c-fos expression is induced in a particular set of brain regions that include the nucleus of the solitary tract (NTS), parabrachial nucleus (PB), central amygdala (CeA), paraventricular hypothalamic nucleus (PVH), supraoptic nucleus (SON) and the circumventricular organs. Within the PVH, the expression is particularly intense in the magnocellular division of the nucleus and it is as yet not clear how this activation occurs. The respective contribution of the vagus afferents and lamina terminalis, which conveys signals entering the brain through the forebrain circumventricular organs, has been investigated in rats subjected to a unilateral cervical vagotomy (UCV) or a unilateral lesion of the fibres running within the lamina terminalis (ULT) and projecting to the neuroendocrine hypothalamus. UCV significantly decreased postprandial c-fos expression in the NTS, PB, CeA and parvocellular division of the PVH. In contrast, ULT impaired postprandial activation of the magnocellular neurons in the PVH and SON. The present study also characterized the types of neurons activated in the PVH and SON during refeeding. In the magnocellular regions, arginine-vasopressin (AVP) neurons were activated upon refeeding whereas there was no apparent induction of Fos expression in oxytocin cells. In the parvocellular PVH, postprandial Fos was induced only in 30% of the corticotrophin-releasing factor (CRF) and AVP neurons. The results of the present study suggest that the postprandial activation of the brain requires the integrity of both the vagal- and lamina terminalis-associated pathways.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Effects of treadmill running on brain activation and the corticotropin-releasing hormone system

The present study was conducted to investigate the effects of treadmill running on the corticotropin-releasing hormone (CRH), CRH receptor type 1 (CRH-R1) and CRH-binding protein (CRH-BP) in the brain of rats that were killed either at rest, immediately after 60 min of treadmill running, or 180 min following a 60-min session of intensive exercise. The expression of the neuronal activity marker c-FOS was also determined in the three conditions of this study. The levels of c-FOS mRNA immediately following running were high in the cortex, caudate-putamen, lateral septum, bed nucleus of the stria terminalis, dorsal and medial thalamus, hypothalamus, pontine nuclei, locus coeruleus and hypoglossal nucleus. In most brain regions investigated, excluding the locus coeruleus and the cingulate cortex, c-FOS mRNA expression returned to control levels after 2 h of recovery. The highest concentration of cells co-expressing the protein Fos and CRH mRNA neurons was found in the parvocellular part of the paraventricular nucleus, which also expressed CRH heteronuclear RNA and CRH-R1 mRNA. The medial preoptic area (MPOA), the medial mammillary nucleus and the posterior hypothalamic as well as the somatosensory cortex, the medial geniculate nucleus, the reticulotegmental nucleus, and Barrington's nucleus also co-expressed Fos and CRH mRNA. The expression of CRH-BP gene was induced in the MPOA following running. In summary, the present study demonstrates that treadmill running leads to a strong expression of c-FOS mRNA that is widely distributed throughout the brain. c-FOS mRNA was found in structures of the somatosensory and somatomotor systems, indicating that these regions were activated during exercise. The pattern of distribution of c-FOS mRNA showed similarities with that triggered by neurogenic and systemic stresses. The present results also indicate that treadmill running can strongly activate the hypophysiotropic CRH system, which suggests, in agreement with the pattern of c-FOS mRNA distribution, that treadmill running has a strong stress component.

Stress activation of cortex and hippocampus is modulated by sex and stage of estrus

Sex plays a major role in stress integration and stress-related affective disease states. Notably, neurocircuits regulating organismic responses to stress are prime targets for central gonadal steroid action. To assess the roles of sex and estrous cycle in central stress integration, we analyzed c-fos mRNA expression in hypothalamic-pituitary-adrenocortical-related regions of stressed male and cycling female (proestrous, estrous, and diestrous) rats. At 60 min after the onset of acute restraint stress, all animal groups showed induction of c-fos mRNA in the frontal cortex, cingulate cortex, piriform cortex, hippocampus, hypothalamic paraventricular nucleus (PVN), medial amygdala, and lateral septum. However, the magnitude of c-fos induction in cortical and hippocampal regions was substantially lower in proestrous and estrous females compared with males and diestrous females. Sex- and estrus cycle-related changes are region specific, as no difference in c-fos induction occurred in the hypothalamic PVN, medial amygdala, or ventrolateral septum in any group. Furthermore, induction of c-fos mRNA in limbic cortexes (but not hippocampus) was positively correlated with progesterone and negatively correlated with ACTH levels. Taken together, this study indicates that cortical structures are differentially stress activated in females depending on the phase of the estrous cycle, perhaps in a progesterone-dependent fashion.