Seasonal and dose-dependent effects of intracerebroventricular leptin on lh secretion and appetite in sheep

The role of leptin in neuroendocrine appetite and reproductive regulation remains to be fully resolved. A series of three experiments was conducted using adequately nourished oestradiol-implanted castrated male sheep. In a cross-over design (n=6), responses to a single i.c.v. (third ventricle) injection of leptin (0.5, 1.0 and 1.5 mg ovine leptin (oLEP) and 1.0 mg murine leptin (mLEP)), N-methyl-D-aspartate (NMDA, 20 micro g) or 0.9% saline (control) were measured in terms of LH secretion (4 h post-injection compared with 4 h pre-injection) and appetite (during 2 h post-injection) in autumn (Experiment 1). NMDA and 1.0 mg oLEP treatments were repeated in the same sheep in the following spring (Experiment 2). With an additional 12 sheep (n=18 in cross-over design), responses to low-dose 'physiological' i.c.v. infusion of leptin (8 ng/h for 12 h daily for 4 days), insulin (0.7 ng/h) and artificial cerebrospinal fluid were measured in the next spring (Experiment 3). LH was studied over 8 h and appetite over 1 h on days 1 and 4 of infusion. In Experiment 1 (autumn), oLEP overall increased LH pulse frequency by up to 110% (P<0.05), decreased LH pulse amplitude (P<0.05) and decreased appetite (P<0.05). mLEP reduced LH pulse amplitude (P<0.05) without significant effect on appetite, while NMDA reduced appetite (P<0.05) but had no effect on LH. In Experiment 2 (spring), LH responses were 'surge-like' with highly significant increases in the moving average LH concentration after 1.0 mg oLEP (P<0.001) and after NMDA (P<0.001). Compared with similar analysis of experiment 1 results, the LH response in spring was greater than that in autumn for both 1.0 mg oLEP (P<0.05) and NMDA (P<0.005). Conversely, unlike in autumn (Experiment 1), there was no effect of 1.0 mg oLEP or NMDA on appetite in the spring (Experiment 2). In Experiment 3 (spring), 'physiological' i.c.v. infusion of oLEP or insulin increased LH pulse frequency by up to 100% (P<0.001) compared with the control infusion on both days 1 and 4, but there were no effects on appetite. These results indicate that intracerebral leptin both stimulates reproductive neuroendocrine output and decreases appetite in adequately nourished sheep. However, the responses of these two axes were dose-dependent and differentially affected by the time of year, suggesting dissociation of the neural pathways involved.     

Cardiovascular Reactivity in Type A and B Males to Mental Arithmetic and Aerobic Exercise at an Equivalent Oxygen Uptake

Cardiovascular hyperreactivity (i.e., response in excess of metabolic requirements) to psychological stress has been implicated in the development of coronary heart disease. The purpose of this study was to evaluate cardiovascular hyperreactivity to psychological stress in Type A and B subjects. Fifteen Type A and 15 Type B young men performed mental arithmetic and cycle ergometry tasks. Linear regressions were calculated for each dependent variable during exercise with oxygen uptake serving as the independent variable. All cardiovascular variables were significantly correlated (p less than .0001) with oxygen uptake during exercise. The regression equations obtained during exercise were then used to predict the value of each cardiovascular variable at the oxygen uptake level obtained during mental arithmetic for each person. Repeated measures ANOVA compared responses observed during arithmetic with responses predicted from exercise at an equivalent oxygen uptake in Type A and B subjects. Heart rate, total peripheral resistance, and mean arterial pressure were significantly greater (p less than .0001) and stroke volume was significantly lower (p less than .0002) during arithmetic than during exercise, while Heather index, cardiac output, and arteriovenous oxygen difference did not differ significantly. No significant differences were found between Type A and B males. Results demonstrated that cardiovascular hyperreactivity was equally robust across Type A and B subjects.     

GLP-1R Agonism Enhances Adjustable Gastric Banding in Diet-Induced Obese Rats

Bariatric procedures vary in efficacy, but overall are more effective than behavioral and pharmaceutical treatment. Roux-en-Y gastric bypass causes increased secretion of glucagon-like peptide 1 (GLP-1) and reduces body weight (BW) more than adjustable gastric banding (AGB), which does not trigger increased GLP-1 secretion. Since GLP-1–based drugs consistently reduce BW, we hypothesized that GLP-1 receptor (GLP-1R) agonists would augment the effects of AGB. Male Long-Evans rats with diet-induced obesity received AGB implantation or sham surgery. GLP-1R agonism, cannabinoid receptor-1 (CB1-R) antagonism, or vehicle was combined with inflation to evaluate interaction between AGB and pharmacological treatments. GLP1-R agonism reduced BW in both sham and AGB rats (left uninflated) compared with vehicle-treated animals. Subsequent band inflation was ineffective in vehicle-treated rats but enhanced weight loss stimulated by GLP1-R agonism. In contrast, there was no additional BW loss when CB1-R antagonism was given with AGB. We found band inflation to trigger neural activation in areas of the nucleus of the solitary tract known to be targeted by GLP-1R agonism, offering a potential mechanism for the interaction. These data show that GLP-1R agonism, but not CB1-R antagonism, improves weight loss achieved by AGB and suggest an opportunity to optimize bariatric surgery with adjunctive pharmacotherapy.Recent years have seen an unprecedented rise in the prevalence of obesity driven by the combination of sedentary lifestyle and exposure to energy-dense diets. This dramatic rise, which is associated with numerous serious comorbidities, has led the World Health Organization to describe obesity as the greatest current threat to human health (1). Conventional therapies, in the form of decreased caloric intake and increased physical activity, have proven to be of limited effectiveness at a population level (2). Similarly, current pharmacotherapies have been found to be only mildly efficacious (3). To this point, surgical intervention is the only method that currently achieves sustained reductions of body weight (BW) >15% (4).Bariatric interventions have proven to be highly efficacious and frequently carry the beneficial side effect of type 2 diabetes (T2D) resolution (5). The most commonly used bariatric procedures are adjustable gastric banding (AGB), vertical sleeve gastrectomy, and Roux-en-Y gastric bypass (RYGB) surgery (6). However, not all of the currently available surgical options are equally effective. AGB results in an average loss of 46% excess BW (5) and a resolution of T2D in 50–70% of individuals (7). Although emerging data may suggest otherwise (8), this procedure is commonly thought of as restrictive in nature. AGB is minimally invasive and reversible but is less effective than RYGB (5); RYGB, a more invasive and irreversible intervention, results in a loss of 60% excess BW on average and is associated with a surprisingly rapid resolution of T2D in ∼80% of patients, but it is also associated with greater mortality (5). We hypothesized that the superior efficacy of RYGB is due to the humoral reprograming observed after RYGB (9) but not AGB (10). Circulating glucagon-like peptide 1 (GLP-1) and therapies based upon it modulate food intake, glucose homeostasis, BW (11), and fat mass (12).Recent research has focused on identifying the factors responsible for the early benefits of RYGB in the hope that novel, nonsurgical therapies might become possible. Although at least some of the beneficial effects of RYGB on glucose control are secondary to reduced BW, the dramatic changes in gut hormone secretion observed in RYGB but not in AGB may contribute to greater resolution of T2D (13). Studies in humans have identified substantial changes in multiple circulating factors, including GLP-1, following RYGB (14). Levels of GLP-1 are greatly elevated after RYGB but not after AGB, suggesting that it may function as a modulator of both BW and glucose homeostasis (15). Given that several diabetes drugs on the market act as GLP-1 receptor (GLP-1R) agonists, modulation of the GLP-1 system may improve less invasive surgical therapies for weight loss and diabetes.We hypothesized that treatment with a GLP-1R agonist would augment weight loss with AGB and that this combined benefit is specific for GLP-1. Taken together, our results suggest that less invasive approaches such as AGB may achieve similar results to RYGB when combined with appropriate pharmacotherapies.     

Allostasis and allostatic load in the context of poverty in early childhood

This paper examined the relation of early environmental adversity associated with poverty to child resting or basal level of cortisol in a prospective longitudinal sample of 1135 children seen at 7, 15, 24, 35, and 48 months of age. We found main effects for poor housing quality, African American ethnicity, and low positive caregiving behavior in which each was uniquely associated with an overall higher level of cortisol from age 7 to 48 months. We also found that two aspects of the early environment in the context of poverty, adult exits from the home and perceived economic insufficiency, were related to salivary cortisol in a time-dependent manner. The effect for the first of these, exits from the home, was consistent with the principle of allostatic load in which the effects of adversity on stress physiology accumulate over time. The effect for perceived economic insufficiency was one in which insufficiency was associated with higher levels of cortisol in infancy but with a typical but steeper decline in cortisol with age at subsequent time points.     

Central infusion of leptin into well-fed and undernourished ewe lambs: effects on feed intake and serum concentrations of growth hormone and luteinizing hormone

Leptin has been implicated in the regulation of feed intake, growth, and reproduction. The objective of this study was to determine if centrally administered leptin would affect feed intake and the secretion of growth hormone (GH) and luteinizing hormone (LH) in ewe lambs. Eighteen ewe lambs were ovariectomized and fitted with intracerebroventricular (i.c.v.) cannulae. Lambs were randomly assigned to receive either a maintenance diet (fed), or a diet that provided 38% of maintenance requirements (diet-restricted) for 14 weeks. Subsequently, recombinant ovine leptin or vehicle was continuously infused, via i.c.v. cannulae, in a linearly increasing dose for 8 days, reaching a maximum of 1.25 microg/kg per h. Feed intake was recorded on days -1 to 7. Blood was collected via jugular cannulae every 10 min for 4 h on days 0, 2, 4, 6 and 8 for the determination of serum leptin, insulin, LH and GH. Leptin suppressed feed intake in fed lambs on days 4 to 7 (P<0.001), but had no effect on feed intake in diet-restricted lambs (P>0.25). Fed lambs had greater serum concentrations of leptin than diet-restricted lambs (P=0.007). Also, although not different on day 0 (pretreatment), on day 8 serum leptin concentrations were greater in leptin-treated lambs than in saline-treated lambs (P=0.003). Insulin was lower in diet-restricted than in fed lambs (P=0.003), but was not affected by leptin treatment (P=0.82). LH pulse frequencies were lower in diet-restricted lambs than in fed lambs (P=0.038), but were not affected by leptin treatment (P=0.85). Mean serum GH was greater in diet-restricted than in fed lambs (P<0.01). In diet-restricted lambs treated with leptin or saline, mean GH did not differ on day 0, but increased in response to leptin treatment (P<0.006). Treatment of fed lambs with leptin did not affect serum GH (P>0.32). From this work, we propose that leptin represents an important functional link between adipose stores and hypothalamic function in ruminants. We demonstrate that leptin concentrations change in response to reduced nutritional status, and that leptin has the ability to regulate multiple physiological processes in lambs, including both feed intake and secretion of GH.     

The Effect of Local Violence on Children’s Attention and Impulse Control

Objectives. We examined whether the burden of violence in a child’s community environment alters the child’s behavior and functioning in the classroom setting.Methods. To identify the effects of local violence, we exploited variation in the timing of local homicides, based on data from the Chicago Police Department, relative to the timing of interview assessments conducted as part of a randomized controlled trial conducted with preschoolers in Head Start programs from 2004–2006, the Chicago School Readiness Project. We compared children’s scores when exposed to recent local violence with scores when no recent violence had occurred to identify causal effects.Results. When children were assessed within a week of a homicide that occurred near their home, they exhibited lower levels of attention and impulse control and lower preacademic skills. The analysis showed strong positive effects of local violence on parental distress, providing suggestive evidence that parental responses may be a likely pathway by which local violence affects young children.Conclusions. Exposure to homicide generates acute psychological distress among caregivers and impairs children’s self-regulatory behavior and cognitive functioning.As one of the leading causes of death among young people, interpersonal violence is an urgent public health problem.1,2 Violence has a disproportionate impact on children, it is highly concentrated in space, and a great deal of evidence suggests that the effects of violence extend beyond the direct victims of assaults or homicides. Direct and indirect exposure to violence is associated with negative health consequences and psychobiological symptoms of distress, such as posttraumatic stress disorder, depression, and difficulty concentrating.3–6 Furthermore, the threat or the experience of violence during childhood can induce high levels of stress, which manifests itself in children’s compromised cognitive functioning, as well as in their academic performance, emotional responses, and social interactions.7–13We considered how the burden of violence in a child’s community can alter the child’s behavior and functioning in the classroom setting. We specifically focused on violence exposure among young children facing socioeconomic disadvantage. Research over the past 2 decades has highlighted stark poverty-related disparities in children’s school readiness as early as kindergarten entry and has underscored poor children’s much higher likelihood of exposure to a wide range of stressful life events, including neighborhood violence.14–17 Yet exposure to violence remains a relatively unexplored pathway through which poor children’s opportunities for learning may be compromised. In examining this pathway, we hypothesized that exposure to extreme community violence, in the form of local homicides, would have an acute impact on children’s ability to regulate behavior, maintain attention, and control impulses in the classroom setting. If local violence affects behavior and performance in the classroom, the results would provide evidence for an additional mechanism by which the problem of community violence extends into key domains of social life, with consequences that have the potential to alter educational trajectories and a range of subsequent health and social outcomes.18–20However, identifying the causal impact of community violence on children’s behavioral and cognitive functioning is difficult because families do not randomly select into violent (or nonviolent) environments.7,21,22 Associations between community violence and children’s outcomes may be a result of unobserved characteristics of families that lead some families to be at higher risk for having to move into (or not being able to move out of) violent community settings.19,23 Those same unobserved parental characteristics may also place children’s likelihood of school success in jeopardy.To address this problem, we departed from the traditional approach to identifying the impact of community violence on children, which involves making comparisons among children living within different communities. Instead, we exploited variation in the timing of local violence—in this case, homicide—relative to the timing of assessments conducted as part of a randomized controlled trial, the Chicago School Readiness Project (CSRP).24,25 The CSRP was designed to assess the effects of a classroom intervention geared toward improving self-regulation and cognitive skills among a sample of students in Head Start classrooms in Chicago. Using data from the CSRP merged with data on homicides across Chicago, we hypothesized that exposure to recent homicides occurring within close geographic proximity to children’s homes affects children’s ability to maintain focus, control impulses, and perform well on tests of preacademic cognitive skills.     

Comparison of R128Q mutations in human, ovine, and chicken leptins

Human leptin and its R128Q mutant, as well as the R128Q mutants of ovine and chicken leptins, were prepared, expressed in Escherichia coli, refolded, and purified to homogeneity yielding electrophoretically pure, over 95% monomeric protein. R128Q mutations did not change the binding properties to BAF/3 cells stably transfected with the long form of human leptin receptor compared, respectively, to non-mutated human, ovine, and chicken leptins. In contrast, the biological activity tested in a proliferation assay in the same cells was drastically changed. Human leptin R128Q lost its activity and even became a weak antagonist, whereas the activities of ovine and chicken leptins were reduced 25- and 80-fold. If dimerization models were applicable leptin receptor activation, the present results would suggest that site 2 of the hormone was impaired. Two models, the human growth hormone:human growth hormone receptor (hGH:hGHR) (1:2) and the granulocyte-colony stimulating factor:granulocyte-colony stimulating factor receptor (GCSF:GCSFR) (2:2) complexes, were used for modeling. Superimposing the leptin structure on the hGH and GCSF models in the complex structures did not indicate any role for R128 in receptor binding. This made it impossible to correlate the results shown in the present work with the currently available models. Therefore, leptin may bind its receptors in a manner different than those proposed until now.