Neuropeptides controlling energy balance: orexins and neuromedins

Serum neopterin and orexin-A levels in different stages of diabetic retinopathy

CLINICAL RELEVANCE

Retinopathy is one of the most common microvascular complications of diabetes mellitus and is the leading cause of vision loss in the working middle-aged population.

BACKGROUND

This study aimed to investigate the value of neopterin and orexin-A levels in patients with diabetes mellitus with different stages of diabetic retinopathy and without diabetic retinopathy and to compare those findings with results from healthy individuals without diabetes mellitus.

METHODS

In total, 65 patients with type 2 diabetes mellitus and 22 healthy individuals without diabetes mellitus were enrolled in this prospective study. The participants were separated into four subgroups. The first subgroup included 25 patients without diabetic retinopathy, the second subgroup included 20 patients non-proliferative diabetic retinopathy, the third subgroup included 20 patients with proliferative diabetic retinopathy, and the fourth subgroup included 22 healthy individuals without diabetes mellitus as controls. Serum neopterin and orexin-A levels were analysed and compared among the groups.

RESULTS

The age and gender of the participants between the four subgroups were not statistically significantly different (p > 0.05). The mean neopterin levels were significantly higher in patients included in the diabetes mellitus subgroups compared with the controls (p < 0.001). Neopterin levels significantly increased as diabetic retinopathy progressed within the diabetes mellitus subgroups. Mean orexin-A levels were significantly lower in the diabetes mellitus subgroups compared with the controls (p < 0.001); however, orexin-A levels were not significantly different within the diabetes mellitus subgroups (p > 0.05).

CONCLUSION

Patients with diabetes mellitus have higher serum neopterin and lower serum orexin-A levels compared with healthy individuals without diabetes mellitus. Moreover, serum neopterin levels increase with progression of diabetic retinopathy.

Interactions between Lateral Hypothalamic Orexin and Dorsal Raphe Circuitry in Energy Balance

Orexin/hypocretin terminals innervate the dorsal raphe nucleus (DRN), which projects to motor control areas important for spontaneous physical activity (SPA) and energy expenditure (EE). Orexin receptors are expressed in the DRN, and obesity-resistant (OR) rats show higher expression of these receptors in the DRN and elevated SPA/EE. We hypothesized that orexin-A in the DRN enhances SPA/EE and that DRN-GABA modulates the effect of orexin-A on SPA/EE. We manipulated orexin tone in the DRN either through direct injection of orexin-A or through the chemogenetic activation of lateral-hypothalamic (LH) orexin neurons. In the orexin neuron activation experiment, fifteen minutes prior to the chemogenetic activation of orexin neurons, the mice received either the GABA-agonist muscimol or antagonist bicuculline injected into the DRN, and SPA/EE was monitored for 24 h. In a separate experiment, orexin-A was injected into the DRN to study the direct effect of DRN orexin on SPA/EE. We found that the activation of orexin neurons elevates SPA/EE, and manipulation of GABA in the DRN does not alter the SPA response to orexin neuron activation. Similarly, intra-DRN orexin-A enhanced SPA and EE in the mice. These results suggest that orexin-A in the DRN facilitates negative energy balance by increasing physical activity-induced EE, and that modulation of DRN orexin-A is a potential strategy to promote SPA and EE.

The role of orexin in fatigue and sleep quality in patients with primary Sjögren's syndrome

BACKGROUND

Sleep disorders and fatigue are prevalent symptoms affecting primary Sjögren's syndrome (pSS) patients. This study aimed to assess the sleep quality of pSS patients as well as its relationship to fatigue and orexin level.

METHODS

This is a cross-sectional study evaluating fatigue in pSS using the Fatigue Severity Scale (FSS). Sleep quality was evaluated using the Pittsburg Sleep Quality Index (PSQI). The European Alliance of Associations for Rheumatology (EULAR) Sjögren's Syndrome Disease Activity Index (ESSDAI) and EULAR Sjögren's Syndrome Patient-Reported Index (ESSPRI) were calculated.

RESULTS

Forty-one patients met the sample criteria and were involved in the final report. They were all females, with a mean (± SD) age and median disease duration of 40.87 ± 10.84 and 36 (6-180) months, respectively. The mean ESSDAI was 0.92 ± 1.3, while the mean ESSPRI was 5.8 ± 2.13. Based on the FSS, 32 (78.04%) patients had a positive test with a mean score of 5.07 ± 1.54. The total PSQI score showed that 60.97% had poor sleep, and the orexin level was lower in patients with pSS than in healthy controls. There was no correlation between orexin level and the presence of fatigue nor the PSQI score.

CONCLUSION

In conclusion, serum orexin levels were lower in patients with pSS than healthy controls, It could be related to impairments in sleep and fatigue in patients with pSS.

The Fidget Factor and the obesity paradox. How small movements have big impact

The hypothesis is that the Fidget Factor is the innate neurological pulse that propels humans and other species to move to support their health. Fidgets, previously thought to be spontaneous, are neurologically regulated and highly ordered (non-random). Modern societies being chair-based overwhelm Fidget Factor pulses and consequently inflict chair-based living for transportation, labor, and leisure. Despite impulses firing through the nervous system, people sit because environmental design overwhelms the biology. Urbanization and chair-based societies were designed after the industrial revolution to promote productivity; however, the consequence has been opposite. Crushing the natural urge to move—the Fidget Factor—is a public health calamity. Excess sitting is associated with a myriad of detrimental health consequences and impairs productivity. Fidgeting may reduce all-cause mortality associated with excessive sitting. The Fidget Factor offers hope; data demonstrate that workplaces and schools can be designed to promote activity and free people's Fidget Factors. Evidence shows that people are happier, healthier, wealthier, and more successful if their Fidget Factors are freed.

Evaluation of Blood Levels of Omentin-1 and Orexin-A in Adults with Obstructive Sleep Apnea: A Systematic Review and Meta-Analysis

Background and objective: Obstructive sleep apnea (OSA) can be related to changes in the levels of adipokines and neuropeptides, which in turn may affect the energy balance components of neuronal cells. Herein, a systematic review and meta-analysis checked the changes in serum/plasma levels of omentin-1 (OM-1: an adipokine) and orexin-A (OXA: a neuropeptide) in adults (age > 18 years old) with OSA (aOSA) compared to controls. Materials and methods: Four databases (Cochrane Library, PubMed, Web of Science, and Scopus) were systematically searched until 14 November 2022, without any restrictions. The Joanna Briggs Institute (JBI) critical appraisal checklist adapted for case−control studies was used to assess the quality of the papers. The effect sizes were extracted using the Review Manager 5.3 software for the blood levels of OM-1 and OXA in aOSA compared with controls. Results: Thirteen articles, with six studies for OM-1 levels and eight for OXA levels, were included. The pooled standardized mean differences were −0.85 (95% confidence interval (CI): −2.19, 0.48; p = 0.21; I2 = 98%) and −0.20 (95%CI: −1.16, 0.76; p = 0.68; I2 = 96%) for OM-1 and OXA levels, respectively. Among the studies reporting OM-1, five were high and one was moderate quality. Among the studies reporting OXA, six were moderate, one was high, and one was low quality. Based on the trial sequential analysis, more participants are needed to confirm the pooled results of the analyses of blood levels of OM-1 and OXA. In addition, the radial plot showed outliers as significant factors for high heterogeneity. Conclusions: The main findings indicated a lack of association between the blood levels of OM-1 and OXA and OSA risk. Therefore, OM-1 and OXA did not appear to be suitable biomarkers for the diagnosis and development of OSA.

Comparative efficacy and safety of lemborexant 5 mg versus 10 mg for the treatment of insomnia: a systematic review

INTRODUCTION

Insomnia is a common condition that may be caused by or coexist with other medical or psychological illnesses. Nearly a quarter of a billion people across the globe suffer from insomnia frequently. Lemborexant, a dual orexin receptor antagonist, is a recently authorized hypnotic-based medication for insomnia. The purpose of this systematic review is to further investigate its efficacy and safety profile, with the primary goal of comparing the effects of two FDA-approved doses of lemborexant, 5 mg and 10 mg (LEM5 and LEM10, respectively).

MATERIALS AND METHODS

PubMed, Google Scholar, ClinicalTrials.gov, and Cochrane Central were searched for relevant literature, and studies were considered if they compared the efficacy and safety of lemborexant 5 mg to lemborexant 10 mg. This study comprised clinical trials.

RESULTS

A total of 6 studies were evaluated for efficacy and safety of lemborexant therapy. They reported a significant betterment in values pertaining to sleep efficacy, sleep onset latency, wake after sleep onset, total sleep time, sleep quality, ISI score, and morning alertness. The results presented a dose-dependent pattern and showed slight variation with the different dosages. The most prevalent side effects noted were somnolence, headaches, and dizziness, with infections like UTIs and upper respiratory tract infections also being commonly reported. The incidence is rather ambiguous and not sincerely dose-dependent. The differences between results for LEM5 and LEM10 do not exhibit a wide variation, although slight dose-dependent alterations are noted.

CONCLUSION

Lemborexant is well integrated with the amelioration of sleep disturbances in insomniac patients, as shown by a decrease in eSOL and sWASO and a rise in sSE, sTST, quality of sleep, and morning alertness. Effects last 12 months after therapy.

Sleep-Wake Disorders in Alzheimer's Disease: A Review

Alzheimer's disease (AD) is a multifactorial disease, and it has become a serious health problem in the world. Senile plaques (SPs) and neurofibrillary tangles (NFTs) are two main pathological characters of AD. SP mainly consists of aggregated β-amyloid (Aβ), and NFT is formed by hyperphosphorylated tau protein. Sleep-wake disorders are prevalent in AD patients; however, the links and mechanisms of sleep-wake disorders on the AD pathogenesis remain to be investigated. Here, we referred to the sleep-wake disorders and reviewed some evidence to demonstrate the relationship between sleep-wake disorders and the pathogenesis of AD. On one hand, the sleep-wake disorders may lead to the increase of Aβ production and the decrease of Aβ clearance, the spreading of tau pathology, as well as oxidative stress and inflammation. On the other hand, the ApoE4 allele, a risk gene for AD, was reported to participate in sleep-wake disorders. Furthermore, some neurotransmitters, such as acetylcholine, glutamate, serotonin, melatonin, and orexins, and their receptors were suggested to be involved in AD development and sleep-wake disorders. We discussed and suggested some possible therapeutic strategies for AD treatment based on the view of sleep regulation. In general, this review explored different views to find novel targets of diagnosis and therapy for AD.

Orexin, serotonin, and energy balance

The lateral hypothalamus is critical for the control of ingestive behavior and spontaneous physical activity (SPA), as lesion or stimulation of this region alters these behaviors. Evidence points to lateral hypothalamic orexin neurons as modulators of feeding and SPA. These neurons affect a broad range of systems, and project to multiple brain regions such as the dorsal raphe nucleus, which contains serotoninergic neurons (DRN) important to energy homeostasis. Physical activity is comprised of intentional exercise and SPA. These are opposite ends of a continuum of physical activity intensity and structure. Non‐goal‐oriented behaviors, such as fidgeting, standing, and ambulating, constitute SPA in humans, and reflect a propensity for activity separate from intentional activity, such as high‐intensity voluntary exercise. In animals, SPA is activity not influenced by rewards such as food or a running wheel. Spontaneous physical activity in humans and animals burns calories and could theoretically be manipulated pharmacologically to expend calories and protect against obesity. The DRN neurons receive orexin inputs, and project heavily onto cortical and subcortical areas involved in movement, feeding and energy expenditure (EE). This review discusses the function of hypothalamic orexin in energy‐homeostasis, the interaction with DRN serotonin neurons, and the role of this orexin‐serotonin axis in regulating food intake, SPA, and EE. In addition, we discuss possible brain areas involved in orexin–serotonin cross‐talk; the role of serotonin receptors, transporters and uptake‐inhibitors in the pathogenesis and treatment of obesity; animal models of obesity with impaired serotonin‐function; single‐nucleotide polymorphisms in the serotonin system and obesity; and future directions in the orexin–serotonin field.

This article is categorized under:

Metabolic Diseases > Molecular and Cellular Physiology

Dopamine receptor 2 downregulation and brain-derived neurotrophic factor upregulation in the paraventricular nucleus are correlated with brown adipose tissue thermogenesis in rats with bilateral substantia nigra lesions

The thermogenesis resulting from brown adipose tissue (BAT)-induced energy consumption is an important method of energy regulation. It has been reported that brain-derived neurotrophic factor (BDNF)-positive neurons in the paraventricular nucleus (PVN) can regulate adaptive thermogenesis in interscapular brown adipose tissue (IBAT), but the upstream regulatory mechanism is still unclear. Our previous studies have found that a large number of dopamine (DA) receptors (DRs) are expressed on BDNF-positive neurons in the PVN and that the substantia nigra (SN) can directly project to the PVN (forming the SN-PVN pathway). Therefore, we speculate that DA in the SN can regulate the expression of BDNF via DRs and then affect IBAT thermogenesis. In this study, bilateral SN lesions were induced in rats with 6-hydroxydopamine (6-OHDA), and the altered expression of DRs and BDNF in the PVN and the metabolic changes in IBAT were studied via double immunofluorescence and western blotting. The results showed that BDNF-positive neurons in the PVN expressed DR 1 (D1) and DR 2 (D2) and were surrounded by a large number of tyrosine hydroxylase (TH)-positive nerve fibers. Compared with the control group, the 6-OHDA group exhibited significantly fewer TH-positive neurons and significantly lower TH expression in the SN, but body weight, IBAT weight and food consumption did not differ between the groups. In the PVN, BDNF expression was upregulated in the 6-OHDA group, while D2 and TH expression was downregulated. In IBAT, the expression of uncoupling protein-1 (UCP-1), phosphorylated hormone-sensitive lipase (p-HSL), TH and β3-adrenergic receptor (β3-AR) was increased, while the expression of fatty acid synthase (FAS) was decreased. The IBAT cell diameter was also decreased in the 6-OHDA group. The results suggest that the SN-PVN pathway may be an upstream neural pathway that can affect BDNF expression in the PVN and that DRs may mediate its regulatory effects. This study expands our understanding of the relationship between DA and obesity.

Dual orexin receptor antagonist (DORA-12) treatment affects the overall levels of Net/maoA mRNA expression in the hippocampus

The orexinergic system plays a significant role in regulating proper sleep/wake maintenance. Dual orexin receptor antagonist (DORA) is widely prescribed for insomnia symptoms. The antagonist acts on orexin 1 and 2 receptors located in certain brain areas, including the locus coeruleus and dorsal raphe. Nevertheless, its effects on monoamine-related gene expression remain unclear. Here, we measured the expression levels of monoamine-related genes in DORA-treated mice. DORA treatment significantly affected overall levels of noradrenalin transporter/monoamine oxidases A mRNA expression in the hippocampus. Our findings suggest that DORA contributes to noradrenalin-related gene expression regulation in the central nervous system.

Acute assessment of subjective appetite and implicated hormones after a hypnosis-induced hallucinated meal: a randomized cross-over pilot trial

The use of hypnosis can generate hallucinatory phenomena, which ranged from vivid/auditory imagery to fully developed "hallucinations" in selected people. The aim of this pilot trial was investigating the acute effects of a hypnosis-induced hallucinated breakfast (HB) compared to those of a real breakfast (RB) on subjective appetite and appetite-regulating hormones in highly hypnotizable individuals. Eight healthy post-menopausal women were recruited to consume two meals: the HB and the RB in a randomized crossover design. Participants underwent appetite sensations measurements (before meal and each 30-min until 270-min) and blood sample collection (at 0, 20, 60, 90, 180-min). A 3-day food-record was filled after each meal. The adjusted repeated measures ANCOVA did not show any meal×time interactions on subjective appetite postprandially. As expected, significantly higher glucose (p < 0.001), insulin (p < 0.001), and lower free fatty acid (p < 0.001) concentrations were found after the RB, but not following HB. Furthermore, RB significantly increased postprandial levels of glucagon-like-peptide-1 and peptide-YY at 20, 60, 90 and 180-min, whereas acylated-ghrelin and leptin levels did not differ. Postprandial neuropeptide-Y and orexin-A values significantly increased at different time-points after RB, but not following HB, while α-melanocyte-stimulating hormone levels enhanced after HB only. Energy intakes were significantly lower after HB on the test-day only (HB = 1146.6 ± 343.8 vs RB = 1634.7 ± 274.2 kcal/d; p = 0.003). Appetite sensation might be modulated by fully developed meal "hallucination" induced by hypnosis, likely affecting brain-peptides implicated in the appetite regulation. However, further studies are needed to verify these results obtained in a highly selected group of individuals. NCT03934580.

Functional characterization of an orexin neuropeptide in amphioxus reveals an ancient origin of orexin/orexin receptor system in chordate

Amphioxus belongs to the subphylum cephalochordata, an extant representative of the most basal chordates, whose regulation of endocrine system remains ambiguous. Here we clearly demonstrated the existence of a functional orexin neuropeptide in amphioxus, which is able to interact with orexin receptor, activate both PKC and PKA pathways, decrease leptin expression, and stimulate lipogenesis. We also showed the transcription level of amphioxus orexin was affected by fasting or temperature, indicating a role of this gene in the regulation of energy balance. In addition, the expression of the amphioxus orexin was detected at cerebral vesicle, which has been proposed to be a homolog of the vertebrate brain. These data collectively suggest that a functional orexin neuropeptide has already emerged in amphioxus, which provide insights into the evolutionary origin of orexin in chordate and the functional homology between the cerebral vesicle and vertebrate brain.

Palatability of Goat's versus Cow's Milk: Insights from the Analysis of Eating Behavior and Gene Expression in the Appetite-Relevant Brain Circuit in Laboratory Animal Models

Goat's (GM) and cow's milk (CM) are dietary alternatives with select health benefits shown in human and animal studies. Surprisingly, no systematic analysis of palatability or preference for GM vs. CM has been performed to date. Here, we present a comprehensive investigation of short-term intake and palatability profiles of GM and CM in laboratory mice and rats. We studied consumption in no-choice and choice scenarios, including meal microstructure, and by using isocaloric milks and milk-enriched solid diets. Feeding results are accompanied by qPCR data of relevant genes in the energy balance-related hypothalamus and brain stem, and in the nucleus accumbens, which regulates eating for palatability. We found that GM and CM are palatable to juvenile, adult, and aged rodents. Given a choice, animals prefer GM- to CM-based diets. Analysis of meal microstructure using licking patterns points to enhanced palatability of and, possibly, greater motivation toward GM over CM. Most profound changes in gene expression after GM vs. CM were associated with the brain systems driving consumption for reward. We conclude that, while both GM and CM are palatable, GM is preferred over CM by laboratory animals, and this preference is driven by central mechanisms controlling eating for pleasure.

An Update on Dual Orexin Receptor Antagonists and Their Potential Role in Insomnia Therapeutics

STUDY OBJECTIVES

Current pharmacological options for the treatment of insomnia insufficiently meet the needs of all insomnia patients. Approved treatments are not consistently effective in improving sleep onset and sleep maintenance, while also having complicated safety profiles. These limitations highlight the unmet need for additional medications and treatment strategies. Initial research suggests that the dual orexin receptor antagonists (DORAs) may offer an additional pharmaceutical option to treat insomnia in some patients.

METHODS

We reviewed the existing literature on dual orexin receptor antagonists in PubMed databases using the search terms "orexin receptor antagonist," "almorexant" "filorexant," "lembroexant" and "suvorexant"; searches were limited to English language primary research articles, clinical trials, and reviews.

RESULTS

Targeting the orexin receptor system for treatment of insomnia offers an additional and alternative pharmacological approach to more common gamma aminobutyric acid agonist sedative hypnotic treatment. Effectiveness is not well established in the current literature; however, the literature does suggest efficacy. Preclinical reports also suggest the potential for treatment in individuals with comorbid Alzheimer disease and insomnia.

CONCLUSIONS

DORAs offer an additional treatment option for insomnia. More clinical trials are needed to robustly evaluate their safety and effectiveness in several subclasses of individuals with insomnia. Given the published literature, head-to-head comparisons to existing treatment for insomnia are warranted.

Microglial Immune Response to Low Concentrations of Combustion-Generated Nanoparticles: An In Vitro Model of Brain Health

The brain is the central regulator for integration and control of responses to environmental cues. Previous studies suggest that air pollution may directly impact brain health by triggering the onset of chronic neuroinflammation. We hypothesize that nanoparticle components of combustion-generated air pollution may underlie these effects. To test this association, a microglial in vitro biological sensor model was used for testing neuroinflammatory response caused by low-dose nanoparticle exposure. The model was first validated using 20 nm silver nanoparticles (AgNP). Next, neuroinflammatory response was tested after exposure to size-selected 20 nm combustion-generated nanoparticles (CGNP) collected from a modern diesel engine. We show that low concentrations of CGNPs promote low-grade inflammatory response indicated by increased pro-inflammatory cytokine release (tumor necrosis factor-α), similar to that observed after AgNP exposure. We also demonstrate increased production of reactive oxygen species and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) p65 phosphorylation in microglia after CGNP stimulation. Finally, we show conditioned media from CGNP-stimulated microglia significantly reduced hypothalamic neuronal survival in vitro. To our knowledge, this data show for the first time that exposure to AgNP and CGNP elicits microglial neuroinflammatory response through the activation of NF-κB.

Exercise counteracts the homeostatic decrease in thermogenesis caused by caloric restriction in sheep

Caloric restriction causes a homeostatic reduction in thermogenesis. We aimed to determine whether exercise could counteract this. We studied four groups of normal-weight ewes ( n = 5), including control sedentary fed ad libitum, exercise fed ad libitum (30 min/d, 5 d/wk), diet-restricted (70% of ad libitum food intake), and combined diet and exercise. Temperature probes implanted in sternal and retroperitoneal adipose tissue and skeletal muscle measured thermogenesis. After the 4-wk intervention, hypothalami were collected for in situ hybridization, and fat and muscle biopsies were collected for real-time PCR and Western blotting. Combined diet and exercise reduced adiposity ( P < 0.05). Caloric restriction alone reduced overnight temperatures in sternal and retroperitoneal fat ( P < 0.05), which was counteracted by exercise ( P < 0.05). Exercise did not induce expression of cellular markers of browning in adipose tissue. There was no effect of diet or exercise on skeletal muscle thermogenesis. Combined diet and exercise increased the expression of neuropeptide Y and agouti-related protein in the hypothalamic arcuate nucleus ( P < 0.05), consistent with reduced adiposity. Gene expressions of key hypothalamic appetite-regulating peptides were not associated with altered thermogenesis. We demonstrate that exercise counteracts the inhibitory effect of caloric restriction to restore thermogenesis in adipose tissue of sheep.-Fuller-Jackson, J.-P., Clarke, I. J., Rao, A., Henry, B. A. Exercise counteracts the homeostatic decrease in thermogenesis caused by caloric restriction in sheep.

Sedentary lifestyle in middle-aged women is associated with severe menopausal symptoms and obesity

OBJECTIVE

The aim of the study was to evaluate the association between sedentary lifestyle and the severity of menopausal symptoms and obesity in middle-aged women.

METHODS

The Menopause Rating Scale, the Goldberg Anxiety and Depression Scale, and the Athens Insomnia Scale were administered to 6,079 Latin American women aged 40 to 59 years. Sedentary lifestyle was defined as fewer than three weekly, 30-minute periods of physical activity.

RESULTS

Sedentary women had more severe menopausal symptoms (total Menopause Rating Scale score: 9.57 ± 6.71 vs 8.01 ± 6.27 points, P < 0.0001) and more depressive symptoms (Goldberg), anxiety (Goldberg), and insomnia (Athens Scale) compared with non-sedentary women. They also had greater mean waist circumference (86.2 ± 12.3 vs 84.3 ± 1.8 cm, P < 0.0001) and a higher prevalence of obesity (20.9% vs 14.3%, P < 0.0001). Logistic regression analysis showed that both obesity (odds ratio [OR] 1.52; 95% CI, 1.32-1.76) and severe menopausal symptoms (OR 1.28; 95% CI, 1.06-1.53), including insomnia and depressive mood, were positively associated with a sedentary lifestyle. Having a stable partner (OR 0.85; 95% CI, 0.76-0.96), using hormone therapy (OR 0.75; 95% CI, 0.64-0.87) and having a higher educational level (OR 0.66; 95% CI, 0.60-0.74) were negatively related to sedentary lifestyle.

CONCLUSIONS

There was a high prevalence of sedentary lifestyle in this middle-aged Latin American female sample which was associated with more severe menopausal symptoms and obesity.

Spontaneous Physical Activity Defends Against Obesity

PURPOSE OF REVIEW

Spontaneous physical activity (SPA) is a physical activity not motivated by a rewarding goal, such as that associated with food-seeking or wheel-running behavior. SPA is often thought of as only "fidgeting," but that is a mischaracterization, since fidgety behavior can be linked to stereotypies in neurodegenerative disease and other movement disorders. Instead, SPA should be thought of as all physical activity behavior that emanates from an unconscious drive for movement.

RECENT FINDINGS

An example of this may be restless behavior, which can include fidgeting and gesticulating, frequent sit-to-stand movement, and more time spent standing and moving. All physical activity burns calories, and as such, SPA could be manipulated as a means to burn calories, and defend against weight gain and reduce excess adiposity. In this review, we discuss human and animal literature on the use of SPA in reducing weight gain, the neuromodulators that could be targeted to this end, and future directions in this field.

Brown and Beige Adipose Tissues in Health and Disease

Brown and beige adipocytes arise from distinct developmental origins. Brown adipose tissue (BAT) develops embryonically from precursors that also give to skeletal muscle. Beige fat develops postnatally and is highly inducible. Beige fat recruitment is mediated by multiple mechanisms, including de novo beige adipogenesis and white-to-brown adipocyte transdifferentiaiton. Beige precursors reside around vasculatures, and proliferate and differentiate into beige adipocytes. PDGFRα+Ebf2+ precursors are restricted to beige lineage cells, while another PDGFRα+ subset gives rise to beige adipocytes, white adipocytes, or fibrogenic cells. White adipocytes can be reprogramed and transdifferentiated into beige adipocytes. Brown and beige adipocytes display many similar properties, including multilocular lipid droplets, dense mitochondria, and expression of UCP1. UCP1-mediated thermogenesis is a hallmark of brown/beige adipocytes, albeit UCP1-independent thermogenesis also occurs. Development, maintenance, and activation of BAT/beige fat are guided by genetic and epigenetic programs. Numerous transcriptional factors and coactivators act coordinately to promote BAT/beige fat thermogenesis. Epigenetic reprograming influences expression of brown/beige adipocyte-selective genes. BAT/beige fat is regulated by neuronal, hormonal, and immune mechanisms. Hypothalamic thermal circuits define the temperature setpoint that guides BAT/beige fat activity. Metabolic hormones, paracrine/autocrine factors, and various immune cells also play a critical role in regulating BAT/beige fat functions. BAT and beige fat defend temperature homeostasis, and regulate body weight and glucose and lipid metabolism. Obesity is associated with brown/beige fat deficiency, and reactivation of brown/beige fat provides metabolic health benefits in some patients. Pharmacological activation of BAT/beige fat may hold promise for combating metabolic diseases. © 2017 American Physiological Society. Compr Physiol 7:1281-1306, 2017.

Appetite-Controlling Endocrine Systems in Teleosts

Mammalian studies have shaped our understanding of the endocrine control of appetite and body weight in vertebrates and provided the basic vertebrate model that involves central (brain) and peripheral signaling pathways as well as environmental cues. The hypothalamus has a crucial function in the control of food intake, but other parts of the brain are also involved. The description of a range of key neuropeptides and hormones as well as more details of their specific roles in appetite control continues to be in progress. Endocrine signals are based on hormones that can be divided into two groups: those that induce (orexigenic), and those that inhibit (anorexigenic) appetite and food consumption. Peripheral signals originate in the gastrointestinal tract, liver, adipose tissue, and other tissues and reach the hypothalamus through both endocrine and neuroendocrine actions. While many mammalian-like endocrine appetite-controlling networks and mechanisms have been described for some key model teleosts, mainly zebrafish and goldfish, very little knowledge exists on these systems in fishes as a group. Fishes represent over 30,000 species, and there is a large variability in their ecological niches and habitats as well as life history adaptations, transitions between life stages and feeding behaviors. In the context of food intake and appetite control, common adaptations to extended periods of starvation or periods of abundant food availability are of particular interest. This review summarizes the recent findings on endocrine appetite-controlling systems in fish, highlights their impact on growth and survival, and discusses the perspectives in this research field to shed light on the intriguing adaptations that exist in fish and their underlying mechanisms.

Inhibition of oxytocin and vasopressin neuron activity in rat hypothalamic paraventricular nucleus by relaxin-3-RXFP3 signalling

KEY POINTS

Relaxin-3 is a stress-responsive neuropeptide that acts at its cognate receptor, RXFP3, to alter behaviours including feeding. In this study, we have demonstrated a direct, RXFP3-dependent, inhibitory action of relaxin-3 on oxytocin and vasopressin paraventricular nucleus (PVN) neuron electrical activity, a putative cellular mechanism of orexigenic actions of relaxin-3. We observed a Gα_i/o -protein-dependent inhibitory influence of selective RXFP3 activation on PVN neuronal activity in vitro and demonstrated a direct action of RXFP3 activation on oxytocin and vasopressin PVN neurons, confirmed by their abundant expression of RXFP3 mRNA. Moreover, we demonstrated that RXFP3 activation induces a cadmium-sensitive outward current, which indicates the involvement of a characteristic magnocellular neuron outward potassium current. Furthermore, we identified an abundance of relaxin-3-immunoreactive axons/fibres originating from the nucleus incertus in close proximity to the PVN, but associated with sparse relaxin-3-containing fibres/terminals within the PVN.

ABSTRACT

The paraventricular nucleus of the hypothalamus (PVN) plays an essential role in the control of food intake and energy expenditure by integrating multiple neural and humoral inputs. Recent studies have demonstrated that intracerebroventricular and intra-PVN injections of the neuropeptide relaxin-3 or selective relaxin-3 receptor (RXFP3) agonists produce robust feeding in satiated rats, but the cellular and molecular mechanisms of action associated with these orexigenic effects have not been identified. In the present studies, using rat brain slices, we demonstrated that relaxin-3, acting through its cognate G-protein-coupled receptor, RXFP3, hyperpolarized a majority of putative magnocellular PVN neurons (88%, 22/25), including cells producing the anorexigenic neuropeptides, oxytocin and vasopressin. Importantly, the action of relaxin-3 persisted in the presence of tetrodotoxin and glutamate/GABA receptor antagonists, indicating its direct action on PVN neurons. Similar inhibitory effects on PVN oxytocin and vasopressin neurons were produced by the RXFP3 agonist, RXFP3-A2 (82%, 80/98 cells). In situ hybridization histochemistry revealed a strong colocalization of RXFP3 mRNA with oxytocin and vasopressin immunoreactivity in rat PVN neurons. A smaller percentage of putative parvocellular PVN neurons was sensitive to RXFP3-A2 (40%, 16/40 cells). These data, along with a demonstration of abundant peri-PVN and sparse intra-PVN relaxin-3-immunoreactive nerve fibres, originating from the nucleus incertus, the major source of relaxin-3 neurons, identify a strong inhibitory influence of relaxin-3-RXFP3 signalling on the electrical activity of PVN oxytocin and vasopressin neurons, consistent with the orexigenic effect of RXFP3 activation observed in vivo.

Impact of Orexin-A Treatment on Food Intake, Energy Metabolism and Body Weight in Mice

Orexin-A and -B are hypothalamic neuropeptides of 33 and 28-amino acids, which regulate many homeostatic systems including sleep/wakefulness states, energy balance, energy homeostasis, reward seeking and drug addiction. Orexin-A treatment was also shown to reduce tumor development in xenografted nude mice and is thus a potential treatment for carcinogenesis. The aim of this work was to explore in healthy mice the consequences on energy expenditure components of an orexin-A treatment at a dose previously shown to be efficient to reduce tumor development. Physiological approaches were used to evaluate the effect of orexin-A on food intake pattern, energy metabolism body weight and body adiposity. Modulation of the expression of brain neuropeptides and receptors including NPY, POMC, AgRP, cocaine- and amphetamine related transcript (CART), corticotropin-releasing hormone (CRH) and prepro-orexin (HCRT), and Y2 and Y5 neuropeptide Y, MC4 (melanocortin), OX1 and OX2 orexin receptors (Y2R, Y5R, MC4R, OX1R and OX2R, respectively) was also explored. Our results show that orexin-A treatment does not significantly affect the components of energy expenditure, and glucose metabolism but reduces intraperitoneal fat deposit, adiposity and the expression of several brain neuropeptide receptors suggesting that peripheral orexin-A was able to reach the central nervous system. These findings establish that orexin-A treatment which is known for its activity as an inducer of tumor cell death, do have minor parallel consequence on energy homeostasis control.

Effect of Housing Types on Growth, Feeding, Physical Activity, and Anxiety-Like Behavior in Male Sprague-Dawley Rats

Background

Animal welfare and accurate data collection are equally important in rodent research. Housing influences study outcomes and can challenge studies that monitor feeding, so housing choice needs to be evidence-based. The goal of these studies was to (1) compare established measures of well-being between rodents housed in wire grid-bottom floors with a resting platform compared to solid-bottom floors with bedding and (2) determine whether presence of a chewable device (Nylabone) affects orexin-A-induced hyperphagia.

Methods

Rodents were crossed over to the alternate housing twice after 2-week periods. Time required to complete food intake measurements was recorded as an indicator of feasibility. Food intake stimulated by orexin-A was compared with and without the Nylabone. Blood corticosterone and hypothalamic BDNF were assessed.

Results

Housing had no effect on growth, energy expenditure, corticosterone, hypothalamic BDNF, behavior, and anxiety measures. Food intake was disrupted after housing cross-over. Time required to complete food intake measurements was significantly higher for solid-bottom bedded cages. The Nylabone had no effect on orexin-A-stimulated feeding.

Conclusion

Well-being is not significantly different between rodents housed on grid-bottom floors and those in solid-bottom-bedded cages based on overall growth and feeding but alternating between housing confounds measures of feeding.

Orexin in Patients with Alcohol Dependence Treated for Relapse Prevention: A Pilot Study

AIM

The aim of the study was to assess the blood concentration of orexin and its association with other clinical factors in patients with alcohol dependence.

METHODS

Thirty-two males hospitalized on an addiction treatment ward due to alcohol dependence and 23 healthy men as a control group were enrolled in the study. The measurement of orexin in the blood was made at the beginning of the treatment (after withdrawal symptoms had stopped) and again after 4 weeks of observation.

RESULTS

At the beginning of the observation, the alcohol-dependent patients had significantly greater orexin blood concentration than the control group. After 4 weeks of treatment for relapse prevention, the blood orexin level decreased significantly to a value similar to that in the control group. At the beginning of the study, more severely alcohol-dependent patients (Short Alcohol Dependence Data [SADD] score range: 20-45) had significantly greater orexin blood concentration than individuals with moderate addiction severity (SADD score range: 10-19). However, after 4 weeks of abstinence, the peptide blood concentration was similar in both groups of alcoholic patients.

CONCLUSIONS

Orexin or its receptor is a potential target for relapse prevention treatment, but further study with long-term observation is needed to verify the usefulness of blood orexin determination as a marker of alcohol relapse risk.

Effect of orexin-A (hypocretin-1) on hyperalgesic and cachectic manifestations of experimentally induced rheumatoid arthritis in rats

Orexin-A has been shown to modulate pain sensation and increase appetite. Rheumatoid arthritis (RA) is characterized by joint destruction, deformity, hyperalgesia, and weight reduction. Aim: Evaluate the possible effect of orexin-A on hyperalgesic and cachectic manifestations in an adjuvant-induced arthritis (AIA) rat model. Methods: Forty adult male Wistar rats were distributed among 4 groups; I, normal controls; II, rats with AIA induced by intradermal injection of Mycobacterium butyricum, but with no other treatment; III, AIA rats treated daily with an intravenous injection of orexin-A for 8 days; and IV, AIA rats treated orally with dexamethasone for 8 days. The parameters we assessed were pain-associated behavior, body mass, hind paw volume, serum levels of nerve growth factor (NGF) and neuropeptide Y (NPY). Results: Orexin-A caused a significant reduction in pain sensation and NGF levels, and increased body mass and the levels of NPY, whereas treatment with dexamethasone led to significant reductions in paw swelling and pain sensation. Conclusion: Orexin-A has hypoalgesic properties and increases body mass, whereas dexamethasone has a potent anti-inflammatory effect. Therefore, the combination of orexin-A and dexamethasone should have a greater effect with respect to attenuating the manifestations and complications associated with RA.

Selection of motor programs for suppressing food intake and inducing locomotion in the Drosophila brain

Central mechanisms by which specific motor programs are selected to achieve meaningful behaviors are not well understood. Using electrophysiological recordings from pharyngeal nerves upon central activation of neurotransmitter-expressing cells, we show that distinct neuronal ensembles can regulate different feeding motor programs. In behavioral and electrophysiological experiments, activation of 20 neurons in the brain expressing the neuropeptide hugin, a homolog of mammalian neuromedin U, simultaneously suppressed the motor program for food intake while inducing the motor program for locomotion. Decreasing hugin neuropeptide levels in the neurons by RNAi prevented this action. Reducing the level of hugin neuronal activity alone did not have any effect on feeding or locomotion motor programs. Furthermore, use of promoter-specific constructs that labeled subsets of hugin neurons demonstrated that initiation of locomotion can be separated from modulation of its motor pattern. These results provide insights into a neural mechanism of how opposing motor programs can be selected in order to coordinate feeding and locomotive behaviors.

Orexin, cardio-respiratory function, and hypertension

In this review we focus on the role of orexin in cardio-respiratory functions and its potential link to hypertension. (1) Orexin, cardiovascular function, and hypertension. In normal rats, central administration of orexin can induce significant increases in arterial blood pressure (ABP) and sympathetic nerve activity (SNA), which can be blocked by orexin receptor antagonists. In spontaneously hypertensive rats (SHRs), antagonizing orexin receptors can significantly lower blood pressure under anesthetized or conscious conditions. (2) Orexin, respiratory function, and central chemoreception. The prepro-orexin knockout mouse has a significantly attenuated ventilatory CO2 chemoreflex, and in normal rats, central application of orexin stimulates breathing while blocking orexin receptors decreases the ventilatory CO2 chemoreflex. Interestingly, SHRs have a significantly increased ventilatory CO2 chemoreflex relative to normotensive WKY rats and blocking both orexin receptors can normalize this exaggerated response. (3) Orexin, central chemoreception, and hypertension. SHRs have higher ABP and SNA along with an enhanced ventilatory CO2 chemoreflex. Treating SHRs by blocking both orexin receptors with oral administration of an antagonist, almorexant (Almxt), can normalize the CO2 chemoreflex and significantly lower ABP and SNA. We interpret these results to suggest that the orexin system participates in the pathogenesis and maintenance of high blood pressure in SHRs, and the central chemoreflex may be a causal link to the increased SNA and ABP in SHRs. Modulation of the orexin system could be a potential target in treating some forms of hypertension.

Orexin, cardio-respiratory function, and hypertension

In this review we focus on the role of orexin in cardio-respiratory functions and its potential link to hypertension. (1) Orexin, cardiovascular function, and hypertension. In normal rats, central administration of orexin can induce significant increases in arterial blood pressure (ABP) and sympathetic nerve activity (SNA), which can be blocked by orexin receptor antagonists. In spontaneously hypertensive rats (SHRs), antagonizing orexin receptors can significantly lower blood pressure under anesthetized or conscious conditions. (2) Orexin, respiratory function, and central chemoreception. The prepro-orexin knockout mouse has a significantly attenuated ventilatory CO₂ chemoreflex, and in normal rats, central application of orexin stimulates breathing while blocking orexin receptors decreases the ventilatory CO₂ chemoreflex. Interestingly, SHRs have a significantly increased ventilatory CO₂ chemoreflex relative to normotensive WKY rats and blocking both orexin receptors can normalize this exaggerated response. (3) Orexin, central chemoreception, and hypertension. SHRs have higher ABP and SNA along with an enhanced ventilatory CO₂ chemoreflex. Treating SHRs by blocking both orexin receptors with oral administration of an antagonist, almorexant (Almxt), can normalize the CO₂ chemoreflex and significantly lower ABP and SNA. We interpret these results to suggest that the orexin system participates in the pathogenesis and maintenance of high blood pressure in SHRs, and the central chemoreflex may be a causal link to the increased SNA and ABP in SHRs. Modulation of the orexin system could be a potential target in treating some forms of hypertension.

Orexin: pathways to obesity resistance?

Obesity has increased in prevalence worldwide, attributed in part to the influences of an obesity-promoting environment and genetic factors. While obesity and overweight increasingly seem to be the norm, there remain individuals who resist obesity. We present here an overview of data supporting the idea that hypothalamic neuropeptide orexin A (OXA; hypocretin 1) may be a key component of brain mechanisms underlying obesity resistance. Prior work with models of obesity and obesity resistance in rodents has shown that increased orexin and/or orexin sensitivity is correlated with elevated spontaneous physical activity (SPA), and that orexin-induced SPA contributes to obesity resistance via increased non-exercise activity thermogenesis (NEAT). However, central hypothalamic orexin signaling mechanisms that regulate SPA remain undefined. Our ongoing studies and work of others support the hypothesis that one such mechanism may be upregulation of a hypoxia-inducible factor 1 alpha (HIF-1α)-dependent pathway, suggesting that orexin may promote obesity resistance both by increasing SPA and by influencing the metabolic state of orexin-responsive hypothalamic neurons. We discuss potential mechanisms based on both animal and in vitro pharmacological studies, in the context of elucidating potential molecular targets for obesity prevention and therapy.

Brain regulation of energy balance and body weight

Body weight is determined by a balance between food intake and energy expenditure. Multiple neural circuits in the brain have evolved to process information about food, food-related cues and food consumption to control feeding behavior. Numerous gastrointestinal endocrine cells produce and secrete satiety hormones in response to food consumption and digestion. These hormones suppress hunger and promote satiation and satiety mainly through hindbrain circuits, thus governing meal-by-meal eating behavior. In contrast, the hypothalamus integrates adiposity signals to regulate long-term energy balance and body weight. Distinct hypothalamic areas and various orexigenic and anorexigenic neurons have been identified to homeostatically regulate food intake. The hypothalamic circuits regulate food intake in part by modulating the sensitivity of the hindbrain to short-term satiety hormones. The hedonic and incentive properties of foods and food-related cues are processed by the corticolimbic reward circuits. The mesolimbic dopamine system encodes subjective "liking" and "wanting" of palatable foods, which is subjected to modulation by the hindbrain and the hypothalamic homeostatic circuits and by satiety and adiposity hormones. Satiety and adiposity hormones also promote energy expenditure by stimulating brown adipose tissue (BAT) activity. They stimulate BAT thermogenesis mainly by increasing the sympathetic outflow to BAT. Many defects in satiety and/or adiposity hormone signaling and in the hindbrain and the hypothalamic circuits have been described and are believed to contribute to the pathogenesis of energy imbalance and obesity.

Role of the locus coeruleus in enhanced orexin A-induced spontaneous physical activity in obesity-resistant rats

Orexin/hypocretin terminals innervate noradrenergic locus coeruleus (LC) neurons that project to the prefrontral cortex, which may influence spontaneous physical activity (SPA) and energy balance. Obesity-resistant (OR) rats have higher orexin receptors (OXR) mRNA in the LC and other brain regions, as well as lower adiposity compared with obese rats. These findings led us to hypothesize that orexin activity in the LC is relevant for the OR phenotype. We compared OR rats to Sprague-Dawley rats. We predicted that: 1) brain OXR expression pattern is sufficient to differentiate OR from non-bred Sprague-Dawley rats; 2) nonresting energy expenditure (NREE) and orexin A (OXA)-stimulated SPA after injection in LC would be greater in OR rats; and 3) the effect of OXA on SPA would be greater than its effect on feeding. OXR mRNA from 11 brain sites and the SPA and feeding responses to OXA in the LC were determined. Body composition, basal SPA, and EE were determined. Principal component analysis of the OXR expression pattern differentiates OR and Sprague-Dawley rats and suggests the OXR mRNA in the LC is important in defining the OR phenotype. Compared with Sprague-Dawley rats, OR rats had greater SPA and NREE and lower resting EE and adiposity. SPA responsivity to OXA in the LC was greater in OR rats compared with Sprague-Dawley rats. OXA in the LC did not stimulate feeding in OR or Sprague-Dawley rats. These data suggest that the LC is a prominent site modulating OXA-stimulated SPA, which promotes lower adiposity and higher nonresting EE.

Orexin modulation of adipose tissue

The orexins are neuropeptides with critical functions in the central nervous system. These neuropeptides have important roles in energy balance and obesity, and therefore on the accumulation of adipose tissue. Rodents lacking orexins, typically through genetic knockouts, experience increased weight gain and accumulation of adipose tissue. Evidence indicates that the lack of the orexins increase adiposity as a result of decreased energy expenditure, principally through a reduction of physical activity. Different lines of evidence suggest that other mechanisms are likely also in play, and neural influences on both white and brown adipose tissues remain to be fully and functionally defined. In addition, the orexin peptides and their receptors are expressed in adipose tissue, with little available information as to their significance. This review summarizes our current understanding of how the orexin peptides affect adipose tissue. We provide a brief introduction to the physiology of orexins and their effects on white and brown adipose tissues in the context of energy balance. We conclude this review by integrating this information in the context of the known physiology of the orexins. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Radiosynthesis and evaluation of [11C]EMPA as a potential PET tracer for orexin 2 receptors

EMPA is a selective antagonist of orexin 2 (OX2) receptors. Previous literature with [(3)H]-EMPA suggest that it may be used as an imaging agent for OX2 receptors; however, brain penetration is known to be modest. To evaluate the potential of EMPA as a PET radiotracer in non-human primate (as a step to imaging in man), we radiolabeled EMPA with carbon-11. Radiosynthesis of [(11)C]N-ethyl-2-(N-(6-methoxypyridin-3-yl)-2-methylphenylsulfonamido)-N-(pyridin-3-ylmethyl)acetamide ([(11)C]EMPA), and evaluation as a potential PET tracer for OX2 receptors is described. Synthesis of an appropriate non-radioactive O-desmethyl precursor was achieved from EMPA with sodium iodide and chlorotrimethylsilane. Selective O-methylation using [(11)C]CH3I in the presence of cesium carbonate in DMSO at room temp afforded [(11)C]EMPA in 1.5-2.5% yield (non-decay corrected relative to trapped [(11)C]CH3I at EOS) with ≥95% chemical and radiochemical purities. The total synthesis time was 34-36min from EOB. Studies in rodent suggested that uptake in tissue was dominated by nonspecific binding. However, [(11)C]EMPA also showed poor uptake in both rats and baboon as measured with PET imaging.

Arrestins in metabolic regulation

This review summarizes the regulatory roles of β-arrestins in whole-body energy balance, body weight control, and carbohydrate and lipid homeostasis. Much research has pointed in the direction of the functions of β-arrestins in mediating desensitization and endocytosis of G protein-coupled receptors as well as in activating the receptor/β-arrestin/ERK signaling pathway being crucial for metabolic regulation. Furthermore, β-arrestins form diverse signal complexes for the activation of the downstream cassettes for the body's metabolic reactions. However, further studies are required to fully address the emerging roles of β-arrestins in metabolic regulation and related diseases.

Orexin A Affects INS-1 Rat Insulinoma Cell Proliferation via Orexin Receptor 1 and the AKT Signaling Pathway

Our aim is to investigate the role of the AKT/PKB (protein kinase B) signaling pathway acting via orexin receptor 1 (OX1R) and the effects of orexin A (OXA) on cell proliferation in the insulin-secreting beta-cell line (INS-1 cells). Rat INS-1 cells were exposed to different concentrations of OXA in vitro and treated with OX1R antagonist (SB334867), PI3K antagonist (wortmannin), AKT antagonist (PF-04691502), or negative control. INS-1 amount of cell proliferation, viability and apoptosis, insulin secretion, OX1R protein expression, caspase-3 activity, and AKT protein levels were determined. We report that OXA (10(-10) to 10(-6) M) stimulates INS-1 cell proliferation and viability, reduces the proapoptotic activity of caspase-3 to protect against apoptotic cell death, and increases insulin secretion. Additionally, AKT phosphorylation was stimulated by OXA (10(-10) to 10(-6) M). However, the OX1R antagonist SB334867 (10(-6) M), the PI3K antagonist wortmannin (10(-8) M), the AKT antagonist PF-04691502 (10(-6) M), or the combination of both abolished the effects of OXA to a certain extent. These results suggest that the upregulation of OXA-OX1R mediated by AKT activation may inhibit cell apoptosis and promote cell proliferation in INS-1 cells. This finding provides functional evidence of the biological actions of OXA in rat insulinoma cells.

Orexin A decreases lipid peroxidation and apoptosis in a novel hypothalamic cell model

Current data support the idea that hypothalamic neuropeptide orexin A (OxA; hypocretin 1) mediates resistance to high fat diet-induced obesity. We previously demonstrated that OxA elevates spontaneous physical activity (SPA), that rodents with high SPA have higher endogenous orexin sensitivity, and that OxA-induced SPA contributes to obesity resistance in rodents. Recent reports show that OxA can confer neuroprotection against ischemic damage, and may decrease lipid peroxidation. This is noteworthy as independent lines of evidence indicate that diets high in saturated fats can decrease SPA, increase hypothalamic apoptosis, and lead to obesity. Together data suggest OxA may protect against obesity both by inducing SPA and by modulation of anti-apoptotic mechanisms. While OxA effects on SPA are well characterized, little is known about the short- and long-term effects of hypothalamic OxA signaling on intracellular neuronal metabolic status, or the physiological relevance of such signaling to SPA. To address this issue, we evaluated the neuroprotective effects of OxA in a novel immortalized primary embryonic rat hypothalamic cell line. We demonstrate for the first time that OxA increases cell viability during hydrogen peroxide challenge, decreases hydrogen peroxide-induced lipid peroxidative stress, and decreases caspase 3/7 induced apoptosis in an in vitro hypothalamic model. Our data support the hypothesis that OxA may promote obesity resistance both by increasing SPA, and by influencing survival of OxA-responsive hypothalamic neurons. Further identification of the individual mediators of the anti-apoptotic and peroxidative effects of OxA on target neurons could lead to therapies designed to maintain elevated SPA and increase obesity resistance.

Innervation of ventricular and periventricular brain compartments

Synaptic transmission is divided into two broad categories on the basis of the distance over which neurotransmitters travel. Wiring transmission is the release of transmitter into synaptic clefts in close apposition to receptors. Volume transmission is the release of transmitters or modulators over varying distances before interacting with receptors. One case of volume transmission over potentially long distances involves release into cerebrospinal fluid (CSF). The CSF contains neuroactive substances that affect brain function and range in size from small molecule transmitters to peptides and large proteins. CSF-contacting neurons are a well-known and universal feature of non-mammalian vertebrates, but only supra- and subependymal serotonergic plexuses are a commonly studied feature in mammals. The origin of most other neuroactive substances in CSF is unknown. In order to determine which brain regions communicate with CSF, we describe the distribution of retrograde neuronal labeling in the rat brain following ventricular injection of Cholera toxin, ß subunit (CTß), a tracer frequently used in brain circuit analysis. Within 15 to 30 min following intraventricular injection, there is only diffuse, non-specific staining adjacent to the ventricular surface. Within 2 to 10 days, however, there is extensive labeling of neuronal perikarya in specific nuclear groups in the telencephalon, thalamus, hypothalamus and brainstem, many at a considerable distance from the ventricles. These observations support the view that ventricular CSF is a significant channel for volume transmission and identifies those brain regions most likely to be involved in this process.