Glucose-sensitive Research Articles

Unacylated Ghrelin Regulates Glucose-Sensitive Neurons Activity and Glycolipid Metabolism via Orexin-A Neurons in the Lateral Hypothalamic Area.

The objective of the study was to investigate the regulatory actions of unacylated ghrelin (UAG) on glucose-sensitive (GS) neurons and glycolipid metabolism in the lateral hypothalamus area (LHA) and its involvement with orexin-A-immunopositive neurons. The effects of UAG administered into the LHA on GS neurons discharges and glycolipid metabolism were detected by single neuron discharge recording, biochemical index analysis and quantitative real-time PCR; the level of c-fos protein in orexin-A-immunopositive neurons was observed using immunofluorescence staining. UAG microinjected into the LHA activated glucose-inhibited neurons, which were partially blocked by pre-administration of anti-orexin-A antibody in the LHA. Furthermore, UAG microinjected into the LHA significantly reduced serum triglycerides (TG), total cholesterol, low-density lipoprotein cholesterol, blood glucose, insulin and hepatic TG levels, while elevated serum high-density lipoprotein cholesterol levels. UAG elevated the mRNA expression of carnitine palmitoyltransferase-1 and reduced the mRNA expression of acetyl-CoA carboxylase-1 in the liver. The above-mentioned effects of UAG were partially blocked by pre-administration of anti-orexin-A antibody. The expressions of orexin-A and c-fos were observed in the LHA. After UAG injection into the LHA, some neurons showed double labeling, and the percentage of double-labeled orexin-A/c-fos neurons in orexin-A-immunopositive neurons increased significantly. UAG in the LHA regulates glycolipid metabolism by activating orexin-A-immunopositive neurons in the LHA.

Glucose-sensitive delivery of metronidazole by using a photo-crosslinked chitosan hydrogel film to inhibit Porphyromonas gingivalis proliferation

A novel glucose-sensitive drug delivery system with controlled release of metronidazole was synthesized by using biocompatible photo-crosslinked chitosan hydrogel film. Specifically, methacrylic anhydride, as photosensitive substance, was firstly grafted on chitosan molecular chains and then UV irradiation was applied as the crosslinking method. Glucose sensitivity was endowed by immobilizing glucose oxidase on the surface of chitosan film. The physicochemical characteristics including chemical composition, crosslinking degree, mechanical strength and related enzyme properties were investigated successively. Cytotoxicity test, drug release and anti-bacterial test were carried out, respectively. The results show that this photo-crosslinked hydrogel film has good mechanical properties; meanwhile, the immobilized enzyme's bonding capacity and activity can maintain a relatively high level after surface activation. In addition, this material possesses better biocompatibility than chemical crosslinked samples. What's more, it can sense the ambient glucose stimulus, rapidly and correspondingly adjust its inner pore structure to control the loaded metronidazole release, lead to an improved antimicrobial activity against Porphyromonas gingivalis under high glucose concentration. This glucose sensitive hydrogel film may provide a promising method for diabetic's periodontitis therapy in clinic.

Orexin-A signaling in the paraventricular nucleus modulates spontaneous firing of glucose-sensitive neurons and promotes food intake via the NPY pathway in rats

Understanding the mechanisms regulating feeding is crucial to unraveling the pathogenesis of obesity. The study primary explored the effects of orexin-A and neuropeptide Y (NPY) signaling in the hypothalamic paraventricular nucleus (PVN) on feeding and glucose-sensitive (GS) neuron activity in rats. Microinjection of orexin-A into the PVN promoted feeding and modulated the spontaneous firing of GS neurons. Those effects were eliminated by pre-injection of the orexin-A receptor-1 (OX1R) antagonist SB-334867 and weaken by the NPY-1 receptor (NPY-1R) antagonist BMS-193885. After orexin-A administration into the PVN, the number of c-fos cells in the arcuate nucleus (ARC) was significantly higher than that in the group receiving normal saline. Furthermore, most cells exhibited co-expression of NPY and c-fos, indicating activation of NPY neurons in the ARC by PVN-administered orexin-A, which might be involved in feeding regulation. These findings indicate that orexin-A and NPY signaling in the PVN are essential to regulating GS neuronal excitability and feeding in rats.

ER Calcium Levels Help Regulate K(ATP) Channel Trafficking to the Plasma Membrane of Pancreatic Beta Cells

The closing of beta cell K(ATP) channels acutely triggers glucose-induced insulin secretion. However, the trafficking of K(ATP) channels to the beta cell plasma membrane has recently been shown to regulate beta cell secretory function over a longer time course, and changes in the number of K(ATP) channels can help set islet glucose sensitivity. To test whether endoplasmic reticulum free calcium level helps control K(ATP) trafficking to the cell surface, insulin-secreting INS-1 cells were treated for 16-18 h. with either palmitate (PALM; 250 µM), the SERCA inhibitor thapsigargin (TG; 200 nM) or tunicamycin (TM; 10 µg/ml); these treatments alter ER Ca. INS-1 membrane fractions were immunoblotted for SUR1, a K(ATP) channel subunit, Glucose Transporter 2 (GLUT2) or Kv2.1 channels. Isolated islets were transfected with the ER Ca sensor D4ER to monitor ER Ca, and basal ER Ca levels were expressed as FRET ratios. TM-treated cells had low levels of glycosylated SUR1 and GLUT2 on their surface membranes whereas the trafficking of Kv2.1 was unaffected. PALM or TG treatment also reduced surface K(ATP), albeit more modestly. To test if ER Ca was reduced due to Ca egress through ER IP3 receptors, we treated cells with xestospongin C (XeC) to inhibit IP3Rs. XeC prevented ER Ca reduction due to TG treatment and increased K(ATP) trafficking. Furthermore, TM or TG treated islets were more glucose sensitive. These data suggest that ER Ca contributes to the control of SUR1 trafficking to the cell surface and/or ER protein processing. Dynamic regulation of surface K(ATP) by ER Ca may provide a novel negative feedback mechanism to regulate beta cell Ca2+ influx.

Meet the Editorial Board

Development of stimuli-sensitive hydrogels for the delivery of drug involves the development of matrices that are glucose-sensitive and have strong sensing properties so that the developed system can sense the level of glucose and release the medicament in response to blood glucose level. In the present study an attempt has been made to develop a glucose sensitive hydrogel system which modulates the release of an anti-diabetic drug in response to the blood glucose level in the body. The hydrogel system was prepared by gas foaming technique using chitosan and polyvinyl alcohol (PVA) as polymer and glutaraldehyde as cross-linking agent. Metformin was used as a drug candidate because of its short biological half life (6.25±0.5 hrs). The prepared glucose sensitive hydrogel system has characterized using different parameters. It was observed that hydrogel swelled and deswelled reversibly depending on the pH and glucose sensitivity of the medium and has suitable mechanical properties. In-vitro results showed that the enzymatically immobilized hydrogel was sensitive to both pH and glucose for effective release of drug. It was found that higher the concentration of glucose in the medium, higher the amount of drug released from the hydrogel. In vivo results showed that glucose oxidase leads to reduction in blood glucose level in response to variable glucose concentration in the body thus achieving the desired therapeutic levels in the body . The present study showed that glucose sensitive hydrogels not only are efficient in controlling the physiological blood glucose level but also provide for a sustained and controlled release of drugs having short biological half life.

Endogenous PYY and GLP‐1 mediate l‐glutamine responses in intestinal mucosa

l-glutamine (Gln) is an energy source for gastrointestinal (GI) epithelia and can stimulate glucagon-like peptide 1 (GLP-1) release from isolated enteroendocrine L-cells. GLP-1 and peptide YY (PYY) are co-secreted postprandially and both peptides have functional roles in glucose homeostasis and energy balance. The primary aim of this project was to establish the endogenous mechanisms underpinning Gln responses within intact GI mucosae using selective receptor antagonists. Mouse mucosae from different GI regions were voltage-clamped and short-circuit current (Isc) was recorded to Gln added to either surface in the absence or presence of antagonists, using wild-type (WT) or PYY-/- tissues. The glucose sensitivity of Gln responses was also investigated by replacement with mannitol. Colonic apical and basolateral Gln responses (at 0.1 and 1 mM) were biphasic; initial increases in Isc were predominantly GLP-1 mediated. GLP-1 receptor antagonism significantly reduced the initial Gln response in the PYY-/- colon. The slower reductions in Isc to Gln were PYY-Y1 mediated as they were absent from the PYY-/- colon and were blocked selectively in WT tissue by a Y1 receptor antagonist. In jejunum mucosa, Gln stimulated monophasic Isc reductions that were PYY-Y1 receptor mediated. Gln effects were partially glucose sensitive, and Calhex 231 inhibition indicated that the calcium-sensing receptor (CaSR) was involved. Gln stimulates the co-release of endogenous GLP-1 and PYY from mucosal L-cells resulting in paracrine GLP-1 and Y1 receptor-mediated electrogenic epithelial responses. This glucose-sensitive mechanism appears to be CaSR mediated and could provide a significant therapeutic strategy releasing two endogenous peptides better known for their glucose-lowering and satiating effects.

Ex vivo generation of glucose sensitive insulin secreting mesenchymal stem cells derived from human adipose tissue

Background:Diabetics are incapable of producing insulin/have autoimmune mechanisms making it ineffective to control glucose secretion. We present a prospective study of glucose-sensitive insulin-secreting mesenchymal stem cells (IS-MSC) generated from human adipose tissue (h-AD) sans xenogenic material.Materials and Methods:Ten grams h-AD from donor anterior abdominal wall was collected in proliferation medium composed of α-Minimum Essential Media (α-MEM), albumin, fibroblast-growth factor and antibiotics, minced, incubated in collagenase-I at 37°C with shaker and centrifuged. Supernatant and pellets were separately cultured in proliferation medium on cell+ plates at 37°C with 5% CO2 for 10 days. Cells were harvested by trypsinization, checked for viability, sterility, counts, flow-cytometry (CD45-/90+/73+), and differentiated into insulin-expressing cells using medium composed of DMEM, gene expressing up-regulators and antibiotics for 3 days. They were studied for transcriptional factors Pax-6, Isl-1, pdx-1 (immunofluorescence). C-peptide and insulin were measured by chemiluminescence. In vitro glucose sensitivity assay was carried out by measuring levels of insulin and C-peptide secretion in absence of glucose followed by 2 hours incubation after glucose addition.Results:Mean IS-AD-MSC quantum was 3.21 ml, cell count, 1.5 ×103 cells/μl), CD45-/90+/73+ cells were 44.37% /25.52%. All of them showed presence of pax-6, pdx-1, and Isl-1. Mean C-Peptide and insulin levels were 0.36 ng/ml and 234 μU/ml, respectively, pre-glucose and 0.87 ng/ml and 618.3 μU/ml post-glucose additions. The mean rise in secretion levels was 2.42 and 2.65 fold, respectively.Conclusion:Insulin-secreting h-AD-MSC can be generated safely and effectively showing in vitro glucose responsive alteration in insulin and C-peptide secretion levels.

Evaluation of glucose sensitive affinity binding assay entrapped in fluorescent dissolved‐core alginate microspheres

The feasibility of dissolved-core alginate-templated fluorescent microspheres as "smart tattoo" glucose biosensors was investigated in simulated interstitial fluid (SIF). The sensor works on the principle of competitive binding and fluorescence resonance energy transfer. The sensor consists of multilayer thin film coated alginate microspheres incorporating dye-labeled glucose receptor and competing ligand within the partially dissolved alginate core. In this study, different approaches for the sensing and detection chemistry were studied, and the response of encapsulated reagents was compared with the solution-phase counterparts. The glucose sensitivity of the encapsulated TRITC-Con A/FITC-dextran (500 kDa) assay in DI water was estimated to be 0.26%/mM glucose while that in SIF was observed to be 0.3%/mM glucose. The glucose sensitivity of TRITC-apo-GOx/FITC-dextran (500 kDa) assay was estimated to be 0.33%/mM glucose in DI water and 0.5%/mM glucose in SIF and both demonstrated a response in the range of 0-50 mM glucose. Therefore, it is hypothesized that the calcium ion concentration outside the microsphere (in the SIF) does not interfere with the response sensitivity. The sensor response was observed to exhibit a maximum response time of 120 s. The system further exhibited a sensitivity of 0.94%/mM glucose with a response in range of 0-50 mM glucose, using near-infrared dyes (Alexa Fluor-647-labeled dextran as donor and QSY-21-conjugated apo-GOx as acceptor), thereby making the sensor more amenable to in vivo use, when implanted in scattering tissue.

Modeling of a glucose sensitive composite membrane for closed-loop insulin delivery

A theoretical model was developed to describe a dynamic process involving an enzymatic reaction and diffusion of reactants and product inside glucose sensitive composite membrane. The composite membrane consisted of nanoparticles of a weakly acidic polymer, glucose oxidase and catalase embedded in a hydrophobic polymer. Time- and position-dependent diffusivity of involved species was considered in the model. Donnan equilibrium was used to find concentrations of buffer ions inside the membrane. The profiles of pH, species concentrations, volume fraction of swollen gel, polymer and water-filled space, as well as solute diffusivity inside the membrane were predicted by the model as a function of step changes of glucose concentration in the external solution. The effects of design parameters and environmental conditions on the glucose responsiveness and insulin permeability of the membrane were studied. The results indicated that the glucose responsiveness of the membrane could be amplified by optimizing the loading of glucose oxidase in the membrane. The glucose sensitivity of the membrane in a phosphate buffer was found to be higher than that in a citrate buffer for a studied membrane formulation. The presented model is a useful numerical tool for the design of glucose-responsive composite membranes for closed-loop insulin delivery.

Brain glucose sensing and body energy homeostasis: role in obesity and diabetes.

The brain has evolved mechanisms for sensing and regulating glucose metabolism. It receives neural inputs from glucosensors in the periphery but also contains neurons that directly sense changes in glucose levels by using glucose as a signal to alter their firing rate. Glucose-responsive (GR) neurons increase and glucose-sensitive (GS) decrease their firing rate when brain glucose levels rise. GR neurons use an ATP-sensitive K+ channel to regulate their firing. The mechanism regulating GS firing is less certain. Both GR and GS neurons respond to, and participate in, the changes in food intake, sympathoadrenal activity, and energy expenditure produced by extremes of hyper- and hypoglycemia. It is less certain that they respond to the small swings in plasma glucose required for the more physiological regulation of energy homeostasis. Both obesity and diabetes are associated with several alterations in brain glucose sensing. In rats with diet-induced obesity and hyperinsulinemia, GR neurons are hyporesponsive to glucose. Insulin-dependent diabetic rats also have abnormalities of GR neurons and neurotransmitter systems potentially involved in glucose sensing. Thus the challenge for the future is to define the role of brain glucose sensing in the physiological regulation of energy balance and in the pathophysiology of obesity and diabetes.

Complex functional attributes of amygdaloid gustatory neurons in the rhesus monkey.

To reveal specific functions of glucose-sensitive (GS) and glucose-insensitive (GIS) cells in chemical information processing, single neuron activity was recorded in the amygdaloid body (AMY) of macaques during: 1) gustatory stimulations and 2) micro-electrophoretic administration of chemicals. Of the 629 neurons tested, 56 (8.9%) responded to, usually two or more, taste qualities. Hedonically distinct tastants usually elicited opposite firing rate changes of the gustatory cells. Seventy percent of the gustatory responses were recorded from GS neurons (17% of all AMY cells). Catecholamines (CAs) induced discharge rate changes in a majority of taste-responsive neurons: The GS gustatory cells were suppressed by norepinephrine (in the form of noradrenaline HCl, NA), whereas the GIS taste-responsive neurons were facilitated by dopamine (DA). Furthermore, NA- and/or DA-antagonists were able to attenuate or suppress taste-elicited responses of several of these cells. These and previous data indicate a specific functional organization of AMY gustatory cells: The GS and GIS taste neurons appear to be involved in differential integration of feeding-associated humoral-metabolic, motivational and exogenous chemical information.

Glucose-sensitive neurons of the globus pallidus: I. Neurochemical characteristics

The lateral hypothalamic area (LHA) and globes pallidtaz (GP) are basically involved in the regulation of feeding and metabolic processes. In the LHA, glucose-sensitive (GS) neurons were described: their activity was found to be specifically suppressed by electrophoretic application of glucose, and these neurons appeared to be also influenced by various feeding-associated neurochemical signals. The main goal of the present experiments was to examine whether similar GS neurons exist in the GP. In addition, neurochemical attributes of the cells were also tested. In anesthetized rats and anesthetized or awake monkeys, single-neuron activity of the GP was recorded by means of carbon fiber multibarreled microelectrodes and the effects of glucose, glutamate (Gt), GABA, dopamine (DA), noradrenaline (NA) and acetylcholine (Ach) were studied. In both the rat and monkey GP, approximately 12% of the neurons examined responded, with inhibition, to glucose. GP neurons, in a high proportion, were also inhibited by GABA and NA. After application of Gt, DA, or Ach, activity increase or decrease occurred. GS neurons exhibited remarkable sensitivity to these neurochemicals previously identified as neurotransmitters of the complex pallidal, extrapyramidel-limbic neuron loops. The results, along with previous data, indicate that GS cells of the GP, while possessing complex neurochemical characteristics, may belong to a hierarchically organized central glucose-monitoring system essential in the regulation of feeding.

Glucose-sensitive neurons of the globus pallidus: II. Complex functional attributes

The globus pallidus (GP) is intimately involved in regulation of various aspects of hunger- and thirst-motivated behaviors. Our parallel neurochernical studies demonstrated the existence of GP neurons whose discharge rates are suppressed by glucose applied microelectrophoretically. In the present series of experiments, we aimed to provide complex, feeding-associated functional characterization—similar to that previously accomplished in the case of lateral hypothalamic and amygdabid chemosensitive neurons—of these glucose-sensitive (GS) and the glucose-insensitive (GIS) pallidal cells. To do so, extracellular single neuron activity of the GP was recorded in anesthetized rats and anesthetized or awake rhesus monkeys by means of carbon fiber, multibarreled glass microelectrodes during: a) microelectrophoretic administration of chemicals, b) gustatory, and c) olfactory stimulations. In alert primates, activity changes were also recorded during presentation of food and nonfood objects as well as during the performance of a conditioned, high fixed-ratio bar-press feeding task. The half of pallidal cells examined showed firing rate changes during phases of the conditioned alimentary task. In both species, about 1/7 of all neurons tested proved to be GS, while the proportion of cells responding to gustatory and olfactory stimulations was 19% and 16%, respectively. Task-related and taste- and smell-responsive units were mainly found among the GS neurons of the pallidum. These data, along with previous findings, indicate that chemosensitive cells of the GP, in an apparent overlap with units of the central gustatory representation, are involved in a hierarchically organized glucose-monitoring neural network, through which pallidal neurons exert their integrative functions in the central feeding control.

Responses of lateral hypothalamic glucose-sensitive and glucose-insensitive neurons to chemical stimuli in behaving rhesus monkeys.

1. Extracellular single neuron activity was recorded in the lateral hypothalamic area (LHA) of awake, behaving monkeys, with particular regard to the feeding-related functional characteristics of glucose-sensitive (GS) versus glucose-insensitive (GIS) neurons. Firing rate changes were recorded by means of carbon fiber, multibarreled glass microelectrodes during 1) microelectrophoretic application of various chemicals, 2) gustatory and olfactory stimulation, and 3) a high fixed-ratio schedule (FR) bar press feeding task. 2. In 336 neurons examined, 91 (27%) were suppressed by electrophoretically administered glucose, and so they were designated as GS cells. The 245 neurons (73%) in which the firing rates did not change during glucose applications were pronounced GIS. The 179 GS and GIS cells tested exhibited different responses to the catecholamines (CAs), noradrenaline (NA) and dopamine (DA), both of which are intimately involved in the control of feeding. More GS neurons responded to NA than did GIS cells; the predominant effect of both CAs on GS neurons was inhibition. 3. The taste responsiveness of 111 LHA neurons was examined. Fifty-seven cells (52%) showed responses to gustatory stimulation. Of 50 GS neurons tested, 33 (66%) exhibited firing rate changes to tastes. On the contrary, only 24 (39%) of the 61 GIS neurons examined responded to gustatory stimuli. Activity changes of GS neurons commonly occurred to two or more tastants, in distinction to the relative gustatory specificity shown by GIS cells. 4. Two hundred fifty-six (84%) of the 303 neurons tested responded during one or more phases of the bar press feeding task. Most activity changes occurred during the bar press (BP) and reward (RW) periods, however numerous phasic responses to cue light (CL) and cue tone (CT) were also observed. A higher proportion of the GS neurons showed task-related activity changes than did the GIS cells (77, 95% and 179, 81%, respectively). GS neurons responded more during the BP phase and to the food reward; GIS cells were more responsive during the CL that enabled acquisition and the CT that signaled reward. Thus GS neurons were responsive during the acquisition and consumption of reward, whereas GIS cells responded to external cues signaling both of these events. The gustatory neurons displayed specific task-related activity changes only in the CL (GIS cells) and BP phases (GS neurons), that is, in phases most intimately involved in sensory-motor integration. 5. Two-thirds of the 30 GS neurons tested were responsive to both gustatory and olfactory stimulation as opposed to only one-third of GIS cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Design of insulin delivery devices based on glucose sensitive membranes

A theoretical model has been developed to evaluate possible designs for an insulin delivery system which is responsive to glucose. The system is based upon a glucose sensitive hydrogel containing immobilized glucose oxidase and catalase. The requirement of molecular oxygen for the enzymic reactions ordinarily limits the response of the system to levels of glucose (less than 50 mg%) below the patho-physiological range (50–1000 mg%) The theoretical model dcveloned desrnbes the transient as well as steady state diffusion and reaction of glucose, oxygen and gluconic acid within the macroporous hydrogel for various designs chosen to alleviate the oxygen limitation. The designs are evaluated in terms of the average pH change within the gel in response to increasing concentrations of glucose. The model predicts the oxygen limitation that has been seen experimentally for a thin glucose sensitive membrane (GSM). The modeling studies have also revealed four device configurations that overcome this limitation. Each design uses silicone rubber to create additional pathways for oxygen delivery to the gel interior. A thin GSM loaded with insulin and placed over a silicone rubber drum, sealed to form a gaseous reservoir, was found to be sensitive to glucose concentrations in the 0–500 mg% range. A second design using a silicone rubber tube filled with GSM (also preloaded with insulin), exhibited glucose sensitivity in the 0–400 mg% range. A combined design, with a central gaseous reservoir bounded by plugs of GSM in a silicone rubber tube, retained a linear response even in the 300–500 rag% range. Finally a fourth design, with an insulin loaded GSM sandwiched between two circular films of silicone rubber sheeting, was sensitive in the 0–200 mg% range. Further considerations of response time, insulin loading and delivery capacity are also discussed.

Functional heterogeneity of the monkey lateral hypothalamus in the control of feeding

Regional differences in the effects of electrical (ES) and chemical stimulation on execution of a bar-press feeding task, and in neuronal activity related to feeding, glucose sensitivity, and odor responsiveness were examined in the lateral hypothalamic area (LHA) of monkeys. In satiated animals, ES of the far lateral and ventral LHA induced bar-press feeding. In hungry animals, ES of the dorsal LHA suppressed the feeding task only during the stimulation period, but prolonged feeding suppression that occurred after ES of the ventromedial LHA. Microinjection of Na-glutamate into LHA sites where ES was effective in suppressing feeding had no effect, but it was effective in the medial hypothalamus. Glucose-sensitive (GS) neurons decreased in activity during bar pressing and/or during the ingestion period. Glucose-insensitive (GIS) neurons showed a cue-related excitation more often than GS neurons. Odor-responding GS and GIS cells were localized in ventromedial and lateral LHA sites, respectively. The present study suggests the regional heterogeneity of the LHA in feeding regulation, depending on both hunger and satiety states.

Taste and olfactory modulation of feeding related neurons in behaving monkey

Single neuron activity in the monkey lateral hypothalamus (LHA) was recorded by multibarreled electrode during a bar press feeding task. Activity of glucose-sensitive (GS) neurons decreased during bar press (BP) and reward (RW) periods. The inhibition was caused by activation of β-adrenoceptors and opioid receptors respectively. Glucose-insensitive (GIS) neurons were excited during BP and RW, and at cue light (CL). Excitation at CL and BP was caused by activation of dopaminergic receptors. Among GS neurons, 66% responded to taste and 88% to odor. These responses were 39% and 52% in GIS neurons. GS neurons responded predominantly to two or more taste and odor stimuli while GIS neurons responded to only one stimulant. GS neurons have dense mutual connections with the prefrontal area, and GIS neurons are connected with the motor area. Gustatory and olfactory stimulation elicited responses in 67% of GS neurons and in only 21% of GIS neurons. Data suggest that GS and GIS neurons may have different functions in feeding: GS neurons process endogenous chemical information and integrated chemical sensations, and GIS neurons process external information processing, motor control and discriminative chemical sensations.

Complex attributes of lateral hypothalamic neurons in the regulation of feeding of alert rhesus monkeys

To elucidate the roles of glucose-sensitive (GS) and glucose-insensitive (GIS) cells of the lateral hypothalamic area (LHA), single neuron activity was recorded during 1) microelectrophoretic administration of chemicals, 2) a conditioned bar press feeding task, 3) gustatory, 4) olfactory, and 5) electrical brain stimulation. GS and GIS neurons showed different firing rate changes during phases of the task, and the responses were highly influenced by the palatability of the food and the motivational (hunger or satiety) state of the animal. The two groups of cells also differed in their responsiveness to gustatory and olfactory stimuli: GS neurons were more likely to respond to tastes and odors than GIS cells. Taste- and odor-responsive GS neurons were primarily suppressed by electrophoretically applied noradrenaline and were localized ventromedially within the LHA. The chemosensitive GIS cells, being organized along a dorsolateral axis, were especially excited by dopamine. The two sets of neurons had distinct connections with associative (orbitofrontal, prefrontal) cortical areas. GS and GIS cells, thus, appear to have differential and complex attributes in the control of feeding.

Comparative study of K channel behavior inβ cell lines with different secretory responses to glucose

The patch-clamp technique was used to identify and investigate two K channels in the cell membrane of the HIT cell, an insulin secreting cell line with glucose-sensitive secretion. Channel characteristics were compared with those of glucose-modulated K channels in the RINm5F cell, an insulin secreting cell line in which secretion is largely glucose insensitive. A 65.7 pS channel, identified with the ATP-sensitive K channel was seen in HIT cell-attached patches. Channel activity was dose-dependently inhibited by glucose, by 50 and 100% at 450 microM and 8 mM glucose, respectively, similar to the values previously reported for RIN cells. In inside-out patches channel activity was 50% inhibited by 56 microM ATP and completely blocked between 500 microM and 1 mM, again, similar to the values reported for RIN cells. As in RIN cells a second, considerably larger (184 pS), K channel was glucose sensitive; the glucose sensitivity was similar to that in RIN cells with 50 and 100% channel inhibition at 7.5 and 25 mM, respectively. After patch excision the mean channel conductance increased from 184 to 215 pS. Under these conditions activity was strongly calcium dependent in the range pCa 5-7, identifying this as a calcium- and voltage-dependent K (K(Ca, V] channel; the calcium sensitivity was similar to that of the adult rat beta cell K(Ca, V) channel. In inside-out RIN cell patches, the large K channel was less abundant but displayed a similar conductance (223 pS). However, its calcium sensitivity was more than 10 times lower than in HIT cells, similar to that of the K(Ca, V) channel in the neonatal rat beta cell, which also displays a reduced secretory response to glucose. Based on these observations, it is proposed that the low calcium sensitivity of the K(Ca, V) channel may be causally associated with secretory deficiency in RIN cells and the immature secretory response of the neonatal beta cell.

Olfactory coding in the monkey lateral hypothalamus: Behavioral and neurochemical properties of odor-responding neurons

The activity of glucose-sensitive (GS) and glucose-insensitive (GIS) neurons was recorded in the lateral hypothalamic area (LHA) of monkeys during olfactory stimulation, a conditioned alimentary bar press task, and microelectrophoretic application of catecholamines. Olfactory stimuli evoked responses of 88% of the GS neurons, and 52% of the GIS cells responded to odors. The GS neurons were more broadly tuned across odorants than the GIS cells, and their responses to various smells with distinct hedonic value were also differential. The odor-responding GS neurons were depressed during the bar press and reward periods of the task, and were mainly inhibited by dopamine. The odor-responding GIS cell activity increased in response to cue light and tone, and was facilitated by dopamine. Histological examinations disclosed topographic dissociation of the odor-responding GS and GIS cells: the former were located in more ventromedial regions than the latter. The results indicate that the GS neurons integrate multiple chemosensory inputs from both endogenous and exogenous sources in the regulation of feeding; whereas the GIS cells distinguish among fewer, more specific cues to control food acquisition behavior.