Effect of palatable diet on growth, caloric intake and endocrine-metabolic profile in weanling rats with dorsomedial hypothalamic lesions

Deletion of Glucocorticoid Receptors in Forebrain GABAergic Neurons Alters Acute Stress Responding and Passive Avoidance Behavior in Female Mice

The glucocorticoid receptor (GR) is critically involved in regulation of stress responses [inhibition of the hypothalamic-pituitary-adrenal (HPA) axis], emotional behavior and cognition via interactions with forebrain corticolimbic circuity. Work to date has largely focused on GR actions in forebrain excitatory neurons; however, recent studies suggest a potential role mediated by interneurons. Here, we targeted GR deletion in forebrain GABAergic neurons, including the cortical interneurons, using a Dlx5/6-Cre driver line to test the role of forebrain interneuronal GR in HPA axis regulation and behavior. Our data indicate that GR deletion in GABAergic neurons causes elevated corticosterone stress responsiveness and decreased cross-over latencies in a passive avoidance task in females, but not males. Dlx5/6-Cre driven gene deletion caused loss of GR in interneurons in the prefrontal cortex (PFC) and hippocampus, but also in select diencephalic GABAergic neurons (including the reticular thalamic nucleus and dorsomedial hypothalamus). Our data suggest that GR signaling in interneurons is differentially important in females, which may have implications for GR-directed therapies for stress-related affective disease states.

Optogenetic activation of leptin- and glucose-regulated GABAergic neurons in dorsomedial hypothalamus promotes food intake via inhibitory synaptic transmission to paraventricular nucleus of hypothalamus

OBJECTIVE

The dorsomedial hypothalamus (DMH) has been considered an orexigenic nucleus, since the DMH lesion reduced food intake and body weight and induced resistance to diet-induced obesity. The DMH expresses feeding regulatory neuropeptides and receptors including neuropeptide Y (NPY), cocaine- and amphetamine-regulated transcript (CART), cholecystokinin (CCK), leptin receptor, and melanocortin 3/4 receptors. However, the principal neurons generating the orexigenic function in the DMH remain to be defined. This study aimed to clarify the role of the DMH GABAergic neurons in feeding regulation by using optogenetics and electrophysiological techniques.

METHODS

We generated the mice expressing ChRFR-C167A, a bistable chimeric channelrhodopsin, selectively in GABAergic neurons of DMH via locally injected adeno-associated virus 2. Food intake after optogenetic activation of DMH GABAergic neurons was measured. Electrophysiological properties of DMH GABAergic neurons were measured using slice patch clamp.

RESULTS

Optogenetic activation of DMH GABAergic neurons promoted food intake. Leptin hyperpolarized and lowering glucose depolarized half of DMH GABAergic neurons, suggesting their orexigenic property. Optical activation of axonal terminals of DMH GABAergic neurons at the paraventricular nucleus of hypothalamus (PVN), where anorexigenic neurons are localized, increased inhibitory postsynaptic currents on PVN neurons and promoted food intake.

CONCLUSION

DMH GABAergic neurons are regulated by metabolic signals leptin and glucose and, once activated, promote food intake via inhibitory synaptic transmission to PVN.

Leptin stimulates neuropeptide Y and cocaine amphetamine-regulated transcript coexpressing neuronal activity in the dorsomedial hypothalamus in diet-induced obese mice

Neuropeptide Y (NPY) neurons in both the arcuate nucleus of the hypothalamus (ARH) and the dorsomedial hypothalamus (DMH) have been implicated in food intake and obesity. However, while ARH NPY is highly expressed in the lean animal, DMH NPY mRNA expression is observed only after diet-induced obesity (DIO). Furthermore, while ARH NPY neurons are inhibited by leptin, the effect of this adipokine on DMH NPY neurons is unknown. In this study we show that in contrast to the consistent expression in the ARH, DMH NPY mRNA expression was undetectable until after 10 weeks in mice fed a high-fat diet, and peaked at 20 weeks. Surprisingly, electrophysiological experiments demonstrated that leptin directly depolarized and increased the firing rate of DMH NPY neurons in DIO mice. To further differentiate the regulation of DMH and ARH NPY populations, fasting decreased expression of DMH NPY expression, while it increased ARH NPY expression. However, treatment with a leptin receptor antagonist failed to alter DMH NPY expression, indicating that leptin may not be the critical factor regulating mRNA expression. Importantly, we also demonstrated that DMH NPY neurons coexpress cocaine amphetamine-regulated transcript (CART); however, CART mRNA expression in the DMH peaked earlier in the progression of DIO. This study demonstrates novel and important findings. First, NPY and CART are coexpressed in the same neurons within the DMH, and second, leptin stimulates DMH NPY neurons. These studies suggest that during the progression of DIO, there is an unknown signal that drives the expression of the orexigenic NPY signal within the DMH, and that the chronic hyperleptinemia increases the activity of these NPY/CART neurons.

Efferent projections of neuropeptide Y-expressing neurons of the dorsomedial hypothalamus in chronic hyperphagic models

The dorsomedial hypothalamus (DMH) has long been implicated in feeding behavior and thermogenesis. The DMH contains orexigenic neuropeptide Y (NPY) neurons, but the role of these neurons in the control of energy homeostasis is not well understood. NPY expression in the DMH is low under normal conditions in adult rodents but is significantly increased during chronic hyperphagic conditions such as lactation and diet-induced obesity (DIO). To understand better the role of DMH-NPY neurons, we characterized the efferent projections of DMH-NPY neurons using the anterograde tracer biotinylated dextran amine (BDA) in lactating rats and DIO mice. In both models, BDA- and NPY-colabeled fibers were limited mainly to the hypothalamus, including the paraventricular nucleus of the hypothalamus (PVH), lateral hypothalamus/perifornical area (LH/PFA), and anteroventral periventricular nucleus (AVPV). Specifically in lactating rats, BDA-and NPY-colabeled axonal swellings were in close apposition to cocaine- and amphetamine-regulated transcript (CART)-expressing neurons in the PVH and AVPV. Although the DMH neurons project to the rostral raphe pallidus (rRPa), these projections did not contain NPY immunoreactivity in either the lactating rat or the DIO mouse. Instead, the majority of BDA-labeled fibers in the rRPa were orexin positive. Furthermore, DMH-NPY projections were not observed within the nucleus of the solitary tract (NTS), another brainstem site critical for the regulation of sympathetic outflow. The present data suggest that NPY expression in the DMH during chronic hyperphagic conditions plays important roles in feeding behavior and thermogenesis by modulating neuronal functions within the hypothalamus, but not in the brainstem.

Differential gene expression between neuropeptide Y expressing neurons of the dorsomedial nucleus of the hypothalamus and the arcuate nucleus: microarray analysis study

The Dorsomedial Nucleus of the Hypothalamus (DMH) is known to play important roles in ingestive behavior and body weight homeostasis. The DMH contains neurons expressing Neuropeptide Y (NPY) during specific physiological conditions of hyperphagia and obesity, however, the role of DMH-NPY neurons has yet to be characterized. In contrast to the DMH-NPY neurons, NPY expressing neurons have been best characterized in the Arcuate Nucleus of the Hypothalamus (ARH). The purpose of this study is to characterize the chemical phenotype of DMH-NPY neurons by comparing the gene expression profiles of NPY neurons in the DMH and ARH isolated from postnatal NPY-hrGFP mice by microarray analysis. Twenty genes were differentially expressed in the DMH-NPY neurons compared to the ARH. Among them, there were several transcriptional factors that play important roles in the regulation of energy balance. DMH-NPY neurons expressed Glutamic Acid Decarboxylase (GAD) 65 and 67, suggesting that they may be GABAergic, similar to ARH-NPY neurons. While ARH-NPY neurons expressed leptin receptor (ObRb) and displayed the activation of STAT3 in response to leptin administration, DMH-NPY neurons showed neither. These findings strongly suggest that DMH-NPY neurons could play a distinct role in the control of energy homeostasis and are differentially regulated from ARH-NPY neurons through afferent inputs and transcriptional regulators.

The dorsomedial hypothalamic nucleus and its role in ingestive behavior and body weight regulation: lessons learned from lesioning studies

This review article discusses the well-established role of the dorsomedial hypothalamic nucleus (DMN) in feeding, drinking and body weight (BW) regulation. DMN lesions (L) in both weanling and mature rats of both sexes produce hypophagia, hypodipsia and reduced ponderal and linear growth in the presence of normal body composition. The growth reduction is not due to a deficient secretion of growth hormone, insulin-like growth factor-1, thyroxine, triiodothyronine or insulin. DMNL rats actively defend their lower BW (BW settling point) by becoming either hyper- or hypophagic, depending on the experimental manipulation, thereby defending both lean and fat mass. They also regulate their 24-h caloric intake, but they may overeat during the first hour of refeeding following a fast, possibly due to a reduced ability to monitor blood glucose or to respond to cholecystokinin (CCK). 2-Deoxy-D-glucose (2DG) increases c-fos expression in orexin-A neurons in the DMN, and DMNL eliminated the orexigenic effect of 2DG. DMNL rats on high-fat diets do not get as obese as controls, which may be due to a reduction of DMN neuropeptide Y (NPY). Rats lacking DMN CCK-A receptors are obese and have increased expression of NPY in the DMN, supporting earlier data that CCK may act at the DMN to suppress food intake. Excitotoxin studies showed that loss of DMN cell somata, and not fibers of passage, is important in the development of the DMNL syndrome. The DMN is a site where opioids increase food intake and knife-cut studies have shown that fibers traveling to/from the DMN are important in this response. An interaction of glucose and opioids in DMN may also be involved in the control of food intake. DMN knife cuts interrupting fibers in the posterior and ventral directions additively produce the hypophagia and reduced linear and ponderal growth observed after DMNL. Ventral cuts may interrupt important connections with the arcuate nucleus. Lateral and posterior DMN cuts additively produce the hypodipsic effect seen after DMNL, but DMNL rats respond normally to all water-regulatory challenges, i.e., the hypophagia is not due to a primary hypodipsia. The DMN has been shown to be involved in the rat's feeding response to an imbalanced amino acid diet. These data show the DMN has an important role in many processes that control both food intake and BW regulation.

Somatic parameters, organ growth, and plasma substrates in weanling rats with lateral hypothalamic lesions one month postoperatively

Somatic and some metabolic aspects of the syndrome that follows bilateral destruction of the lateral hypothalamic area (LHA) have been studied primarily in mature rats. Fewer data are available for the weanling rat. Weanling Sprague-Dawley rats received small (10 mC) bilateral electrolytic lesions (LHAL). Sham-operated controls were pair-gained to LHAL rats (CON-PG) or fed ad lib (CON-ADLIB). All rats were killed 1 month after LHAL. Both LHAL and CON-PG weighed less, had less carcass fat, and were shorter than CON-ADLIB. Also, LHAL were somewhat, but significantly (SIGN), shorter than CON-PG. Rats with LHAL has less carcass protein than CON-ADLIB in percent but not in absolute terms. Liver, epididymal fat pads, diaphragm, kidneys adrenals, testes, spleen, and heart grew SIGN smaller in LHAL vs. CON-ADLIB, but in no instance was there a SIGN difference between LHAL and CON-PG. In body weight percentage, some of these differences (liver, kidneys, heart) were not SIGN. Both LHAL and CON-PG had larger adrenals than CON-ADLIB and both LHAL and CON-PG had SIGN less protein in their livers, epididymal fat pads, and diaphragm than CON-ADLIB. In organ weight percentage, however, LHAL rats had more protein in their livers and fat pads than CON-ADLIB and LHAL rats had less protein in fat pads than CON-PG in absolute but not in percent organ weight terms. Plasma glucose was similar in all groups, but LHAL had SIGN lower triglycerides and total cholesterol than CON-ADLIB.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormone and somatic changes in rats pair-fed to growth retarded dorsomedial hypothalamic nuclei-lesioned rats

Rats with dorsomedial hypothalamic nuclei lesions (DMNL) are hypophagic and have reduced linear and ponderal growth, but have normal body composition and anabolic hormone concentrations. Previous studies have shown rats pair-fed to levels consumed (70-80% of ad lib) by DMNL rats, using a meal-feeding paradigm, have abnormal body composition and hormone concentrations. Whether the noted changes were due to restriction per se or method of food presentation was uncertain. In the present study, one group of sham-operated rats was pair fed (SHPF) by a computer-operated system that presented 45 mg food pellets in the exact amount and pattern as their DMNL yoked partner; another sham-operated group was ad lib fed (SHAD). At the end of Experiment 1 (11 days) and Experiment 2 (3 weeks) blood was collected for hormone and metabolite analyses; body compositions were also determined. Unlike an earlier report, the DMNL and SHPF groups had normal percentage body fat. Percentage carcass protein was similar in all groups at 11 days, but slightly elevated in DMNL rats at 3 weeks. Also, in contrast to an earlier study, plasma-free fatty acid levels were comparable in DMNL and SHPF rats. Plasma insulin was normal in the DMNL and SHPF rats at 11 days, but was lowered (p < 0.05) in the SHPF group at 3 weeks. Plasma thyroxine was reduced (p < 0.01) in the SHPF group at 11 days but returned to normal by 3 weeks. Thyroxine and triiodothyronine levels were normal in the DMNL groups. Plasma corticosterone levels were similar in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Brown (BAT) and white (WAT) adipose tissue in high-fat junk food (HFJF) and chow-fed rats with dorsomedial hypothalamic lesions (DMNL rats)

Male weanling rats received dorsomedial hypothalamic nucleus lesions (DMNL) or sham operations and were fed for 173 postoperative days a high-fat diet and given a 32% sucrose solution as drinking fluid. This was supplemented with chocolate chip cookies, potato chips and marshmallows. Other DMNL and sham-operated controls were fed lab chow instead of the above high-fat junk food diet (HFJF) and given tap water instead of 32% sucrose solution. All animals were killed on postoperative day 174. Caloric intake per 100 g body weight was similar in all groups; however, the HFJF fed control and DMNL rats had significantly elevated carcass fat. Since HFJF-DMNL rats were not nearly as obese as the HFJF control animals, it appears that the DMNL offered some protection against the HFJF-diet-produced obesity. When their smaller body size is considered. DMN lesions had no effect on brown adipose tissue (BAT) mass in chow-fed or HFJF fed rats, whereas BAT size was significantly enlarged in HFJF-fed control animals. This suggests but does not prove that HFJF-fed controls, but not DMNL rats, may be using dietary-induced thermogenesis (DIT) to attenuate their obesity. We hypothesize that the HFJF-fed DMNL may not be enhancing DIT as reflected in normal BAT size, because they had not attained a degree of fatness to activate this system, or the DMN lesions impaired its activation. Both HFJF-fed groups showed reduced linear growth compared to their counterparts. The reason for stunting is uncertain, but may be related to their low plasma insulin concentrations.

Experimental obesity: a homeostatic failure due to defective nutrient stimulation of the sympathetic nervous system

The basic hypothesis of this review is that studies on models of experimental obesity can provide insight into the control systems regulating body nutrient stores in humans. In this homeostatic or feedback approach to analysis of the nutrient control system, we have examined the afferent feedback signals, the central controller, and the efferent control elements regulating the controlled system of nutrient intake, storage, and oxidation. The mechanisms involved in the beginning and ending of single meals must clearly be related to the long-term changes in fat stores, although this relationship is far from clear. Changes in total nutrient storage in adipose tissue can arise as a consequence of changes in the quantity of nutrients ingested in one form or another or a decrease in the utilization of the ingested nutrients. A change in energy intake can be effected by increased size of individual meals, increased number of meals in a 24-hour period, or a combination of these events. Similarly, a decrease in utilization of these nutrients can develop through changes in resting metabolic energy expenditure which are associated with one of more of the biological cycles such as protein metabolism, triglyceride for glycogen synthesis and breakdown, or maintenance of ionic gradients for Na+ + K+ across cell walls. In addition, differences in energy expenditure related to the thermogenesis of eating or to the level of physical activity may account for differences in nutrient utilization.