Karen A. Scott

Leptin activates hypothalamic acetyl-CoA carboxylase to inhibit food intake

Hypothalamic fatty acid metabolism has recently been implicated in the controls of food intake and energy homeostasis. We report that intracerebroventricular (ICV) injection of leptin, concomitant with inhibiting AMP-activated kinase (AMPK), activates acetyl-CoA carboxylase (ACC), the key regulatory enzyme in fatty acid biosynthesis, in the arcuate nucleus (Arc) and paraventricular nucleus (PVN) in the hypothalamus. Arc overexpression of constitutively active AMPK prevents the Arc ACC activation in response to ICV leptin, supporting the hypothesis that AMPK lies upstream of ACC in leptins Arc intracellular signaling pathway. Inhibiting hypothalamic ACC with 5-tetradecyloxy-2-furoic acid, a specific ACC inhibitor, blocks leptin-mediated decreases in food intake, body weight, and mRNA level of the orexigenic neuropeptide NPY. These results show that hypothalamic ACC activation makes an important contribution to leptins anorectic effects. Furthermore, we find that ICV leptin up-regulates the level of malonyl-CoA (the intermediate of fatty acid biosynthesis) specifically in the Arc and increases the level of palmitoyl-CoA (a major product of fatty acid biosynthesis) specifically in the PVN. The rises of both levels are blocked by 5-tetradecyloxy-2-furoic acid along with the blockade of leptin-mediated hypophagia. These data suggest malonyl-CoA as a downstream mediator of ACC in leptins signaling pathway in the Arc and imply that palmitoyl-CoA, instead of malonyl-CoA, could be an effector in relaying ACC signaling in the PVN. Together, these findings highlight site-specific impacts of hypothalamic ACC activation in leptins anorectic signaling cascade.

Role of dorsomedial hypothalamic neuropeptide Y in modulating food intake and energy balance.

Previous studies have suggested that neuropeptide Y (NPY) in the dorsomedial hypothalamus (DMH) serves as an important signaling peptide in the regulation of energy balance. To elucidate such actions, we used the adenoassociated virus (AAV) system to alter Npy gene expression in the DMH and examined the effects of these alterations on food intake and energy balance as well as explored its downstream signaling pathway. We found that AAV-mediated overexpression of NPY in the DMH of lean rats increased food intake and body weight, and exacerbated high-fat diet-induced obesity. Knockdown of NPY expression in the DMH via AAV-mediated RNA interference ameliorated the hyperphagia, obesity, and diabetes of Otsuka Long–Evans Tokushima Fatty (OLETF) rats. NPY knockdown in the DMH produced a nocturnal and meal size-specific feeding effect. Moreover, we found that knockdown of DMH NPY expression in intact rats reduced NPY content in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus and affected within-meal satiation. DMH NPY knockdown increased the feeding inhibitory and NTS c-Fos responses to peripheral administration of cholecystokinin. Together, these results indicate that DMH NPY plays an important role in modulating food intake and energy balance and its dysregulation causes disordered energy balance leading to obesity.

Transferring the blues: Depression-associated gut microbiota induces neurobehavioural changes in the rat.

The gut microbiota interacts with the host via neuroimmune, neuroendocrine and neural pathways. These pathways are components of the brain-gut-microbiota axis and preclinical evidence suggests that the microbiota can recruit this bidirectional communication system to modulate brain development, function and behaviour. The pathophysiology of depression involves neuroimmune-neuroendocrine dysregulation. However, the extent to which changes in gut microbiota composition and function mediate the dysregulation of these pathways is unknown. Thirty four patients with major depression and 33 matched healthy controls were recruited. Cytokines, CRP, Salivary Cortisol and plasma Lipopolysaccharide binding protein were determined by ELISA. Plasma tryptophan and kynurenine were determined by HPLC. Fecal samples were collected for 16s rRNA sequencing. A Fecal Microbiota transplantation was prepared from a sub group of depressed patients and controls and transferred by oral gavage to a microbiota-deficient rat model. We demonstrate that depression is associated with decreased gut microbiota richness and diversity. Fecal microbiota transplantation from depressed patients to microbiota-depleted rats can induce behavioural and physiological features characteristic of depression in the recipient animals, including anhedonia and anxiety-like behaviours, as well as alterations in tryptophan metabolism. This suggests that the gut microbiota may play a causal role in the development of features of depression and may provide a tractable target in the treatment and prevention of this disorder.

Effects of Chronic Social Stress on Obesity

The prevalence of overweight and obesity has markedly increased during the past few decades. Stress has been suggested as one environmental factor that may contribute to the development of obesity. In this review, we discuss the role that exposure to chronic stress may play in the development of obesity, with particular attention to the effects of chronic psychosocial stress. Of particular importance is the effect that social stress has on dietary preference, food consumption, and regional distribution of adipose tissue. We present evidence from human and animal studies that links sympathetic nervous system and hypothalamic-pituitary-adrenal axis hyperactivity with visceral obesity, and that stress tends to alter the pattern of food consumption, and promotes craving of nutrient-dense “comfort foods.” Lastly, we discuss the visible burrow system, a model of chronic social stress used in our laboratory to assess the effects of social subordination on behavioral and metabolic profile.

Angiotensin Type 1 Receptors in the Subfornical Organ Mediate the Drinking and Hypothalamic-Pituitary-Adrenal Response to Systemic Isoproterenol

Circulating angiotensin II (ANGII) elicits water intake and activates the hypothalamic-pituitary-adrenal (HPA) axis by stimulating angiotensin type 1 receptors (AT1Rs) within circumventricular organs. The subfornical organ (SFO) and the organum vasculosum of the lamina terminalis (OVLT) are circumventricular organs that express AT1Rs that bind blood-borne ANGII and stimulate integrative and effector regions of the brain. The goal of these studies was to determine the contribution of AT1Rs within the SFO and OVLT to the water intake and HPA response to increased circulating ANGII. Antisense oligonucleotides directed against the AT1R [AT1R antisense (AT1R AS)] were administered into the OVLT or SFO. Quantitative receptor autoradiography confirmed that AT1R AS decreased ANGII binding in the SFO and OVLT compared with the scrambled sequence control but did not affect AT1R binding in other nuclei. Subsequently, water intake, ACTH, and corticosterone (CORT) were assessed after administration of isoproterenol, a beta-adrenergic agonist that decreases blood pressure and elevates circulating ANGII. Delivery of AT1R AS into the SFO attenuated water intake, ACTH, and CORT after isoproterenol, whereas similar treatment in the OVLT had no effect. To determine the specificity of this blunted drinking and HPA response, the same parameters were measured after treatment with hypertonic saline, a stimulus that induces drinking independently of ANGII. Delivery of AT1R AS into the SFO or OVLT had no effect on water intake, ACTH, or CORT after hypertonic saline. The results imply that AT1R within the SFO mediate drinking and HPA responses to stimuli that increase circulating ANGII.

Central angiotensin II has catabolic action at white and brown adipose tissue

Considerable evidence implicates the renin-angiotensin system (RAS) in the regulation of energy balance. To evaluate the role of the RAS in the central nervous system regulation of energy balance, we used osmotic minipumps to chronically administer angiotensin II (Ang II; icv; 0.7 ng/min for 24 days) to adult male Long-Evans rats, resulting in reduced food intake, body weight gain, and adiposity. The decrease in body weight and adiposity occurred relative to both ad libitum- and pair-fed controls, implying that reduced food intake in and of itself does not underlie all of these effects. Consistent with this, rats administered Ang II had increased whole body heat production and oxygen consumption. Additionally, chronic icv Ang II increased uncoupling protein-1 and β(3)-adrenergic receptor expression in brown adipose tissue and β3-adrenergic receptor expression in white adipose tissue, which is suggestive of enhanced sympathetic activation and thermogenesis. Chronic icv Ang II also increased hypothalamic agouti-related peptide and decreased hypothalamic proopiomelanocortin expression, consistent with a state of energy deficit. Moreover, chronic icv Ang II increased the anorectic corticotrophin- and thyroid-releasing hormones within the hypothalamus. These results suggest that Ang II acts in the brain to promote negative energy balance and that contributing mechanisms include an alteration in the hypothalamic circuits regulating energy balance, a decrease in food intake, an increase in energy expenditure, and an increase in sympathetic activation of brown and white adipose tissue.

Glucose Parameters Are Altered in Mouse Offspring Produced by Assisted Reproductive Technologies and Somatic Cell Nuclear Transfer

Fortunately, the majority of children conceived through assisted reproductive technologies (ARTs) appear healthy; however, metabolic abnormalities, including elevated glucose and increased and altered adipose tissue deposition, have been reported in adolescents. To parse out factors that may be responsible, we investigated the effects of two different ARTs—in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI)—as well as somatic cell nuclear transfer (SCNT) on glucose clearance, body weight, and body composition of young adult mice. Female and male mice generated through ART weighed more than control (naturally conceived [STOCK]) mice at birth. No differences in body weight were observed in males up to 8 wk of age. ART females took longer than control mice to clear a glucose bolus, with glucose clearance most impaired in SCNT females. IVF females secreted more insulin and had a higher insulin peak 15 min after glucose injection compared with all other groups. Male mice exhibited no differences in glucose clearance, but IVF males required more insulin to do so. SCNT females weighed more than IVF, ICSI, and STOCK females, and they had higher fat content than ICSI females and higher leptin levels than all other groups. These results show that glucose parameters are altered in young adult mice conceived through techniques associated with ART before onset of obesity and may be responsible for its development later in life. The present study suggests that more investigation regarding the long-term effects of manipulations associated with ART is warranted.

Blood-Borne Angiotensin II Acts in the Brain to Influence Behavioral and Endocrine Responses to Psychogenic Stress

This study elucidates the neural circuits by which circulating angiotensin II (ANGII) acts in the brain to influence humoral and behavioral responses to psychological stressors. To test the hypothesis that systemic ANGII mediates stress responding via the subfornical organ (SFO), we first found that the timing of increased systemic ANGII in response to 60 min restraint coincides with increased c-fos mRNA expression in the SFO. Next, we administered an anterograde neuronal tract tracer into the SFO and found that fibers originating there make appositions onto neurons in the paraventricular nucleus of the hypothalamus that are also c-fos positive following restraint stress. To determine whether circulating ANGII stimulates the release of stress hormones via activation of angiotensin type 1 receptors (AT1R) within the SFO, we delivered lentivirus to knockdown AT1R expression locally in the SFO. Inhibition of AT1R specifically within the SFO blunted the release of adrenocorticotrophin-releasing hormone and corticosterone in response to restraint stress and caused rats to spend more time in the open arms of an elevated-plus maze than controls, indicating that inhibition of AT1R within the SFO is anxiolytic. Collectively, these results suggest that circulating ANGII acts on AT1R in the SFO to influence responding to psychological stressors.

Acute exposure to a high-fat diet alters meal patterns and body composition.

Weight gain and adiposity are often attributed to the overconsumption of unbalanced, high-fat diets however, the pattern of consumption can also contribute to associated body weight and compositional changes. The present study explored the rapid alterations in meal patterns of normal-weight rats given continuous access to high-fat diet and examined body weight and composition changes compared to chow fed controls. Ten Long-Evans rats were implanted with subcutaneous microchips for meal pattern analysis. Animals were body weight matched and separated into two groups: high-fat or chow fed. Each group was maintained on their assigned diet for nine days and monitored for 22 h each day for meal pattern behavior. Body weight was evaluated every other day, and body composition measures were taken prior and following diet exposure. High-fat fed animals gained more weight and adipose tissue than chow fed controls and displayed a reduced meal frequency and increased meal size. Furthermore, meal size was significantly correlated with the gain of adipose tissue. Together, these results suggest that consumption of a high-fat diet can rapidly alter meal patterns, which in turn contribute to the development of adiposity.

Meal patterns and hypothalamic NPY expression during chronic social stress and recovery

In the present study, we examined meal patterns during and after exposure to the visible burrow system (VBS), a rodent model of chronic social stress, to determine how the microstructure of food intake relates to the metabolic consequences of social subordination. Male Long-Evans rats were housed in mixed-sex VBS colonies (4 male, 2 female) for 2 wk, during which time a dominance hierarchy formed [1 dominant male (DOM) and 3 subordinate males (SUB)], and then male rats were individually housed for a 3-wk recovery period. Controls were individually housed with females during the 2-wk VBS period and had no changes in ingestive behavior compared with a habituation period. During the hierarchy-formation phase of VBS housing, DOM and SUB had a reduced meal frequency, whereas SUB also had a reduced meal size. However, during the hierarchy-maintenance phase of VBS housing, DOM meal patterns did not differ from controls, whereas SUB continued to display a reduced food intake via less frequent meals. During recovery, DOM had comparable meal patterns to controls, whereas SUB had an increased meal size. Hypothalamic neuropeptide Y (NPY) mRNA levels were not different between these groups during the experimental period. Together, the results suggest that exposure to chronic social stress alters ingestive behavior both acutely and in the long term, which may influence the metabolic changes that accompany bouts of stress and recovery; however, these differences in meal patterns do not appear to be mediated by hypothalamic NPY.