Wake-promoting effects of orexin: Its independent actions against the background of an impaired corticotropine-releasing hormone receptor system

Neuroimmune connections between corticotropin-releasing hormone and mast cells: novel strategies for the treatment of neurodegenerative diseases

Corticotropin-releasing hormone is a critical component of the hypothalamic–pituitary–adrenal axis, which plays a major role in the body’s immune response to stress. Mast cells are both sensors and effectors in the interaction between the nervous and immune systems. As first responders to stress, mast cells can initiate, amplify and prolong neuroimmune responses upon activation. Corticotropin-releasing hormone plays a pivotal role in triggering stress responses and related diseases by acting on its receptors in mast cells. Corticotropin-releasing hormone can stimulate mast cell activation, influence the activation of immune cells by peripheral nerves and modulate neuroimmune interactions. The latest evidence shows that the release of corticotropin-releasing hormone induces the degranulation of mast cells under stress conditions, leading to disruption of the blood-brain barrier, which plays an important role in neurological diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, autism spectrum disorder and amyotrophic lateral sclerosis. Recent studies suggest that stress increases intestinal permeability and disrupts the blood-brain barrier through corticotropin-releasing hormone-mediated activation of mast cells, providing new insight into the complex interplay between the brain and gastrointestinal tract. The neuroimmune target of mast cells is the site at which the corticotropin-releasing hormone directly participates in the inflammatory responses of nerve terminals. In this review, we focus on the neuroimmune connections between corticotropin-releasing hormone and mast cells, with the aim of providing novel potential therapeutic targets for inflammatory, autoimmune and nervous system diseases.

Corticotropin-Releasing Factor and Toll-Like Receptor Gene Expression Is Associated with Low-Grade Inflammation in Irritable Bowel Syndrome Patients with Depression

The mechanism of low-grade inflammation in irritable bowel syndrome (IBS) is unclear; our research concentrates on the involvement of the corticotropin-releasing factor (CRF) and Toll-like receptor (TLR) gene expression in the process of low-grade inflammation in IBS patients with depression. This study suggests more IBS patients are presenting with the states of depression and anxiety. IBS patients with depression have shown a lower grade inflammatory response and an imbalance of the inflammatory response. CRF1, CRF2, TLR2, and TLR4 in IBS patients with depression are significantly higher than those without depression and controls. Thus, activation of the CRF-TLR associated pathways produces an inflammatory reaction, which can concurrently affect the digestive tract and the CNS and induce the corresponding digestive and psychiatric symptoms.

A role for orexin in cytotoxic chemotherapy-induced fatigue

Fatigue is the most common symptom related to cytotoxic chemotherapeutic treatment of cancer. Peripheral inflammation associated with cytotoxic chemotherapy is likely a causal factor of fatigue. The neural mechanisms by which cytotoxic chemotherapy associated inflammation induces fatigue behavior are not known. This lack of knowledge hinders development of interventions to reduce or prevent this disabling symptom. Infection induced fatigue/lethargy in rodents is mediated by suppression of hypothalamic orexin activity. Orexin is critical for maintaining wakefulness and motivated behavior. Though there are differences between infection and cytotoxic chemotherapy in some symptoms, both induce peripheral inflammation and fatigue. Based on these similarities we hypothesized that cytotoxic chemotherapy induces fatigue by disrupting orexin neuron activity. We found that a single dose of a cytotoxic chemotherapy cocktail (cyclophosphamide, adriamycin, 5-fluorouracil - CAF) induced fatigue/lethargy in mice and rats as evidenced by a significant decline in voluntary locomotor activity measured by telemetry. CAF induced inflammatory gene expression - IL-1R1 (p<0.001), IL-6 (p<0.01), TNFα (p<0.01), and MCP-1 (p<0.05) - in the rodent hypothalamus 6-24h after treatment during maximum fatigue/lethargy. CAF decreased orexin neuron activity as reflected by decreased nuclear cFos localization in orexin neurons 24h after treatment (p<0.05) and by decreased orexin-A in cerebrospinal fluid 16 h after treatment (p<0.001). Most importantly, we found that central administration of 1 μg orexin-A restored activity in CAF-treated rats (p<0.05). These results demonstrate that cytotoxic chemotherapy induces hypothalamic inflammation and that suppression of hypothalamic orexin neuron activity has a causal role in cytotoxic chemotherapy-induced fatigue in rodents.

Nesfatin-1/NUCB2 as a potential new element of sleep regulation in rats

Study Objectives

Millions suffer from sleep disorders that often accompany severe illnesses such as major depression; a leading psychiatric disorder characterized by appetite and rapid eye movement sleep (REMS) abnormalities. Melanin-concentrating hormone (MCH) and nesfatin-1/NUCB2 (nesfatin) are strongly co - expressed in the hypothalamus and are involved both in food intake regulation and depression. Since MCH was recognized earlier as a hypnogenic factor, we analyzed the potential role of nesfatin on vigilance.

Design

We subjected rats to a 72 h-long REMS deprivation using the classic flower pot method, followed by a 3 h-long ‘rebound sleep’. Nesfatin mRNA and protein expressions as well as neuronal activity (Fos) were measured by quantitative in situ hybridization technique, ELISA and immunohistochemistry, respectively, in ‘deprived’ and ‘rebound’ groups, relative to controls sacrificed at the same time. We also analyzed electroencephalogram of rats treated by intracerebroventricularly administered nesfatin-1, or saline.

Results

REMS deprivation downregulated the expression of nesfatin (mRNA and protein), however, enhanced REMS during ‘rebound’ reversed this to control levels. Additionally, increased transcriptional activity (Fos) was demonstrated in nesfatin neurons during ‘rebound’. Centrally administered nesfatin-1 at light on reduced REMS and intermediate stage of sleep, while increased passive wake for several hours and also caused a short-term increase in light slow wave sleep.

Conclusions

The data designate nesfatin as a potential new factor in sleep regulation, which fact can also be relevant in the better understanding of the role of nesfatin in the pathomechanism of depression.

Deficiency of corticotropin-releasing hormone type-2 receptor alters sleep responses to bacterial lipopolysaccharide in mice

In response to infectious stimuli, enhanced non-rapid eye movement sleep (NREMS) occurs, which is driven by pro-inflammatory cytokines. Those cytokines further elicit the release of corticotropin-releasing hormone (CRH), resulting in the activation of the hypothalamic-pituitary-adrenocortical axis. Signals of CRH are mediated by two receptor types, namely CRH-R1 and -R2. The role of CRH-R1 in wake-promoting effects of CRH has been rather clarified, whereas the involvement of CRH-R2 in sleep-wake regulation is poorly understood. To investigate whether CRH-R2 interferes with sleep responses to immune challenge, this study examined effects of bacterial lipopolysaccharide (LPS) on sleep in CRH-R2 deficient (KO) mice. CRH-R2 KO mice and control littermates (CL) were implanted with electrodes for recording electroencephalogram (EEG) and electromyogram. After recovery, LPS was applied by intraperitoneal injection at doses of 0.1, 1.0, or 10 μg at dark onset. In response to LPS injection NREMS of both genotypes was enhanced in a dose-dependent manner. However, CRH-R2 KO mice showed a larger increase, in particular after 10 μg of LPS compared to CL mice. During postinjection, reduced delta power for NREMS was detected in both genotypes after each dose, but the highest dose evoked a marked elevation of EEG activity in a limited frequency band (4 Hz). However, the EEG power of lower frequencies (1-2 Hz) increased more in CRH-R2 KO than in CL mice. The results indicated that CRH-R2 KO mice show greater NREMS responses to LPS, providing evidence that CRH-R2 participates in sleep-wake regulation via an interaction with the activated immune system.