In vitro autoradiographic localization of amylin binding sites in rat brain

Amylin-like immunoreactivity in the extra-islet peptide YY-producing and glucagon-immunoreactive cells in Japanese quail pancreas

In this study, we investigated amylin-like substance distribution in the pancreas of Japanese quail (Coturnix japonica) using a specific anti-rat amylin serum. We detected amylin-immunoreactive cells dispersed in the pancreatic extra-islet region but not in the islet region. The synthetic rat amylin-containing serum pre-absorption abolished the staining profile. Almost all amylin-immunoreactive cells were immuno-positive for peptide YY (PYY). In addition, certain amylin-immunoreactive cells stained immuno-positive for glucagon. Amylin and PYY co-secreted from the extra-islet cells might participate in the insulin and glucagon release regulation in the pancreas and food intake modulation through the central nervous system.

The processing intermediate of human amylin, pro-amylin(1-48), has in vivo and in vitro bioactivity

Amylin is released by pancreatic beta-cells in response to a meal and its major soluble mature form (37 amino acid-peptide) produces its biological effects by activating amylin receptors. Amylin is derived from larger propeptides that are processed within the synthesizing beta-cell. There are suggestions that a partially processed form, pro-amylin(1-48) is also secreted. We tested the hypothesis that pro-amylin(1-48) has biological activity and that human pro-amylin(1-48) may also form toxic pre-amyloid species. Amyloid formation, the ability to cross-seed and in vitro toxicity were similar between human pro-amylin(1-48) and amylin. Human pro-amylin(1-48) was active at amylin-responsive receptors, though its potency was reduced at rat, but not human amylin receptors. Pro-amylin(1-48) was able to promote anorexia by activating neurons of the area postrema, amylin's primary site of action, indicating that amylin can tolerate significant additions at the N-terminus without losing bioactivity. Our studies help to shed light on the possible roles of pro-amylin(1-48) which may be relevant for the development of future amylin-based drugs.

Novel mechanisms involved in leptin sensitization in obesity

Leptin is a hormone that is secreted by adipocytes in proportion to adipose tissue size, and that informs the brain about the energy status of the body. Leptin acts through its receptor LepRb, expressed mainly in the hypothalamus, and induces a negative energy balance by potent inhibition of feeding and activation of energy expenditure. These actions have led to huge expectations for the development of therapeutic targets for metabolic complications based on leptin-derived compounds. However, the majority of patients with obesity presents elevated leptin production, suggesting that in this setting leptin is ineffective in the regulation of energy balance. This resistance to the action of leptin in obesity has led to the development of "leptin sensitizers," which have been tested in preclinical studies. Much research has focused on generating combined treatments that act on multiple levels of the gastrointestinal-brain axis. The gastrointestinal-brain axis secretes a variety of different anorexigenic signals, such as uroguanylin, glucagon-like peptide-1, amylin, or cholecystokinin, which can alleviate the resistance to leptin action. Moreover, alternative mechanism such as pharmacokinetics, proteostasis, the role of specific kinases, chaperones, ER stress and neonatal feeding modifications are also implicated in leptin resistance. This review will cover the current knowledge regarding the interaction of leptin with different endocrine factors from the gastrointestinal-brain axis and other novel mechanisms that improve leptin sensitivity in obesity.

Non-fibril form but not fibril form of human islet amyloid polypeptide 8-20 changes brain functions in mice

Whether fibril formation increases or decreases cytotoxicity remains unclear. Aggregation of human islet amyloid polypeptide (hIAPP), a pivotal regulator of glucose homeostasis, impairs the function and viability of pancreatic β cells. Evidence suggests that low-order oligomers of hIAPP are more toxic to β cells than fibril. However, it remains unclear whether non-fibril form of hIAPP specifically alters brain functions. This study produced fibril and non-fibril forms from a single hIAPP 8-20 peptide. The non-fibril form-injected mice showed changes in spontaneous motor activities, preference for location in the open field and social behavior. In contrast, the fibril-injected mice showed no changes in these behavioral tests. In line with the behavioral changes, the non-fibril form led to impaired neurite outgrowth of cultured neuron-like cells and the loss of neurons in the mouse hippocampus. These findings suggest that non-fibril form but not fibril form of hIAPP changes brain functions.

Obesity: A Review of Pathophysiology and Classification

Obesity is a chronic, multifactorial, and morbid disease. In the United States, 69% of adults are overweight or have obesity, and the global prevalence of obesity is increasing. Obesity is influenced by genetic, neurologic, metabolic, enteric, and behavioral processes. It remains a key modifiable risk factor for many comorbid diseases, including cardiovascular disease, diabetes mellitus, and cancer. Whereas there are recent and significant advances in obesity therapy, including diets, lifestyle modifications, pharmacotherapies, endoscopic procedures, and bariatric surgeries, there is an immense need for a better understanding of the heterogeneity in the pathophysiologic process of obesity and outcomes. Here we review salient pathophysiologic mechanisms underlying the development and morbidity of obesity as well as pathophysiologically based classification systems that inform current obesity management and may inform improved and individualized management in the future.

Calcitonin receptor signaling in nucleus accumbens D1R- and D2R-expressing medium spiny neurons bidirectionally alters opioid taking in male rats

The high rates of relapse associated with current medications used to treat opioid use disorder (OUD) necessitate research that expands our understanding of the neural mechanisms regulating opioid taking to identify molecular substrates that could be targeted by novel pharmacotherapies to treat OUD. Recent studies show that activation of calcitonin receptors (CTRs) is sufficient to reduce the rewarding effects of addictive drugs in rodents. However, the role of central CTR signaling in opioid-mediated behaviors has not been studied. Here, we used single nuclei RNA sequencing (snRNA-seq), fluorescent in situ hybridization (FISH), and immunohistochemistry (IHC) to characterize cell type-specific patterns of CTR expression in the nucleus accumbens (NAc), a brain region that plays a critical role in voluntary drug taking. Using these approaches, we identified CTRs expressed on D1R- and D2R-expressing medium spiny neurons (MSNs) in the medial shell subregion of the NAc. Interestingly, Calcr transcripts were expressed at higher levels in D2R- versus D1R-expressing MSNs. Cre-dependent viral-mediated miRNA knockdown of CTRs in transgenic male rats was then used to determine the functional significance of endogenous CTR signaling in opioid taking. We discovered that reduced CTR expression specifically in D1R-expressing MSNs potentiated/augmented opioid self-administration. In contrast, reduced CTR expression specifically in D2R-expressing MSNs attenuated opioid self-administration. These findings highlight a novel cell type-specific mechanism by which CTR signaling in the ventral striatum bidirectionally modulates voluntary opioid taking and support future studies aimed at targeting central CTR-expressing circuits to treat OUD.

Metabolic Hormone Action in the VTA: Reward-Directed Behavior and Mechanistic Insights

Dysfunctional signaling in midbrain reward circuits perpetuates diseases characterized by compulsive overconsumption of rewarding substances such as substance abuse, binge eating disorder, and obesity. Ventral tegmental area (VTA) dopaminergic activity serves as an index for how rewarding stimuli are perceived and triggers behaviors necessary to obtain future rewards. The evolutionary linking of reward with seeking and consuming palatable foods ensured an organism's survival, and hormone systems that regulate appetite concomitantly developed to regulate motivated behaviors. Today, these same mechanisms serve to regulate reward-directed behavior around food, drugs, alcohol, and social interactions. Understanding how hormonal regulation of VTA dopaminergic output alters motivated behaviors is essential to leveraging therapeutics that target these hormone systems to treat addiction and disordered eating. This review will outline our current understanding of the mechanisms underlying VTA action of the metabolic hormones ghrelin, glucagon-like peptide-1, amylin, leptin, and insulin to regulate behavior around food and drugs of abuse, highlighting commonalities and differences in how these five hormones ultimately modulate VTA dopamine signaling.

The increase in the number of amylin neurons in the medial preoptic area throughout the lactational period and its relationship with melanin-concentrating hormone

The amylin and the melanin-concentrating hormone [MCH] are two peptides related to energetic homeostasis. During lactation, it is possible to locate neurons expressing these peptides in the preoptic area of rat dams. In addition, it was demonstrated that the number of MCH neurons in this region is modulated by litter size. Taken together, the aims of this work were (1) to verify the time course of amylin immunoreactivity during lactation; (2) to verify whether litter size modulates the number of amylin-ir neurons (3) to verify whether there is colocalization between the amylin-ir and MCH-ir neurons. Our results show that (1) there is an increase in the number of amylin-ir neurons during lactation, which reaches a peak at postpartum day 19 and drastically reduces after weaning; (2) there is no correlation between litter size and the number of amylin-ir neurons; and (3) there is minimal overlap between amylin-ir and MCH-ir neurons.

Interactions of Polyphenolic Gallotannins with Amyloidogenic Polypeptides Associated with Alzheimer's Disease: From Molecular Insights to Physiological Significance

Polyphenols are natural compounds abundantly found in plants. They are known for their numerous benefits to human health, including antioxidant properties and anti-inflammatory activities. Interestingly, many studies have revealed that polyphenols can also modulate the formation of amyloid fibrils associated with disease states and can prevent the formation of cytotoxic oligomer species. In this review, we underline the numerous effects of four hydrolysable gallotannins (HGTs) with high conformational flexibility, low toxicity, and multi-targeticity, e.g., tannic acid, pentagalloyl glucose, corilagin, and 1,3,6-tri-O-galloyl-β-D-glucose, on the aggregation of amyloidogenic proteins associated with the Alzheimer's Disease (AD). These HGTs have demonstrated interesting abilities to reduce, at different levels, the formation of amyloid fibrils involved in AD, including those assembled from the amyloid β-peptide, the tubulin-associated unit, and the islet amyloid polypeptide. HGTs were also shown to disassemble pre-formed fibrils and to diminish cognitive decline in mice. Finally, this manuscript highlights the importance of further investigating these naturally occurring HGTs as promising scaffolds to design molecules that can interfere with the formation of proteotoxic oligomers and aggregates associated with AD pathogenesis.

Actions of feeding-related peptides on the mesolimbic dopamine system in regulation of natural and drug rewards

The mesolimbic dopamine system is the primary neural circuit mediating motivation, reinforcement, and reward-related behavior. The activity of this system and multiple behaviors controlled by it are affected by changes in feeding and body weight, such as fasting, food restriction, or the development of obesity. Multiple different peptides and hormones that have been implicated in the control of feeding and body weight interact with the mesolimbic dopamine system to regulate many different dopamine-dependent, reward-related behaviors. In this review, we summarize the effects of a selected set of feeding-related peptides and hormones acting within the ventral tegmental area and nucleus accumbens to alter feeding, as well as food, drug, and social reward.

Mediators of Amylin Action in Metabolic Control

Amylin (also called islet amyloid polypeptide (IAPP)) is a pancreatic beta-cell hormone that is co-secreted with insulin in response to nutrient stimuli. The last 35 years of intensive research have shown that amylin exerts important physiological effects on metabolic control. Most importantly, amylin is a physiological control of meal-ending satiation, and it limits the rate of gastric emptying and reduces the secretion of pancreatic glucagon, in particular in postprandial states. The physiological effects of amylin and its analogs are mediated by direct brain activation, with the caudal hindbrain playing the most prominent role. The clarification of the structure of amylin receptors, consisting of the calcitonin core receptor plus receptor-activity modifying proteins, aided in the development of amylin analogs with a broad pharmacological profile. The general interest in amylin physiology and pharmacology was boosted by the finding that amylin is a sensitizer to the catabolic actions of leptin. Today, amylin derived analogs are considered to be among the most promising approaches for the pharmacotherapy against obesity. At least in conjunction with insulin, amylin analogs are also considered important treatment options in diabetic patients, so that new drugs may soon be added to the only currently approved compound pramlintide (Symlin^®). This review provides a brief summary of the physiology of amylin’s mode of actions and its role in the control of the metabolism, in particular energy intake and glucose metabolism.

Calcitonin receptor antibody validation and expression in the rodent brain

BACKGROUND AND AIM

Therapeutics that reduce calcitonin gene-related peptide activity are effective migraine treatments. However, gaps remain in our understanding of the molecular mechanisms that link calcitonin gene-related peptide to migraine. The amylin 1 receptor responds potently to calcitonin gene-related peptide, and to the related peptide amylin, but its role in relation to either peptide or to migraine is unclear. We sought to better understand the expression of the amylin 1 receptor protein subunit, the calcitonin receptor, in the rodent brain.

METHODS

We profiled three antibodies for immunodetection of calcitonin receptor, using immunocytochemistry, western blotting, and calcitonin receptor conditional knockout mouse tissue. Selected migraine-relevant rat brain regions were then examined for calcitonin receptor-like immunoreactivity.

RESULTS

All three antibodies detected calcitonin receptor protein but only one (188/10) produced robust immunostaining in rodent brain, under the conditions used. Calcitonin receptor-like immunoreactivity was apparent in the rat brainstem and midbrain including the locus coeruleus, periaqueductal grey and spinal trigeminal nucleus.

CONCLUSIONS

Anti-calcitonin receptor antibodies require comprehensive profiling to ensure confidence in the detection of calcitonin receptor. Using a validated antibody, calcitonin receptor-like immunoreactivity was detected in several brain regions relevant to migraine. Further research is needed to understand the functional consequences of calcitonin receptor expression for calcitonin gene-related peptide or amylin physiology and pathophysiology.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Peripherally administered amylin inhibits stress-like behaviors and enhances cognitive performance

Amylin, a 37 amino acid peptide pancreatic hormone co-secreted with insulin, normalizes the altered eating patterns induced by chronic stress in the rat. Because these stress-induced changes are driven, in part, by brain corticotropin-releasing factor and corticosterone, and because alterations in the activity of these molecules and the stress system are commonly associated with neuropsychiatric diseases like anxiety, depression, and schizophrenia, we hypothesized that amylin might mitigate behavioral states associated with stress. Therefore, we tested the effects of rat amylin in rodent-based behavioral assays sensitive to neuropsychiatric drugs, including anxiolytic, antidepressant, antipsychotic, and cognitive enhancing drugs: stress-induced hyperthermia (SIH); marble burying; elevated plus maze (EPM)), forced swim test (FST), pre-pulse inhibition, and phencyclidine-induced locomotion. To assess the neural underpinnings of amylin's anxiolytic-like effects, we examined the effect of amylin on SIH after lesioning the area postrema (AP), which mediates amylin's metabolic effects. Amylin injection (IP, 0.1, 1.0, & 10 mg/kg) significantly (P < 0.05) decreased SIH (97% below vehicle) and AP lesions inhibited this effect. Amylin also reduced marble burying (72% below vehicle), but had no effect in the EPM. Together, these effects suggest anxiolytic-like activity or potential. Amylin injection also enhanced cognitive performance in the novel object recognition test. When administered continuously by implanted osmotic pumps, amylin (300 mg/kg/d) blocked SIH when tested at 1 and 4 weeks. Compared to vehicle, amylin infusion (1 and 3 mg/kg/d) reduced the time immobile in the FST (P < 0.05; 30% below vehicle), suggesting antidepressant-like potential. Although further testing is needed, our findings support a potential for peripherally administered amylin to access and benefit pathways that regulate memory, emotion, and mood.

Amylin Pharmacology in Alzheimer's Disease Pathogenesis and Treatment

The metabolic peptide hormone amylin, in concert with other metabolic peptides like insulin and leptin, has an important role in metabolic homeostasis and has been intimately linked to Alzheimer's disease (AD). Interestingly, this pancreatic amyloid peptide is known to self-aggregate much like amyloid-beta and has been reported to be a source of pathogenesis in both Type II diabetes mellitus (T2DM) and Alzheimer's disease. The traditional "gain of toxic function" properties assigned to amyloid proteins are, however, contrasted by several reports highlighting neuroprotective effects of amylin and a recombinant analog, pramlintide, in the context of these two diseases. This suggests that pharmacological therapies aimed at modulating the amylin receptor may be therapeutically beneficial for AD development, as they already are for T2DMM. However, the nature of amylin receptor signaling is highly complex and not well studied in the context of CNS function. Therefore, to begin to address this pharmacological paradox in amylin research, the goal of this review is to summarize the current research on amylin signaling and CNS functions and critically address the paradoxical nature of this hormone's signaling in the context of AD pathogenesis.

Anatomical Organization of the Rat Subfornical Organ

The subfornical organ (SFO) is a sensory circumventricular organ located along the anterodorsal wall of the third ventricle. SFO lacks a complete blood-brain barrier (BBB), and thus peripherally-circulating factors can penetrate the SFO parenchyma. These signals are detected by local neurons providing the brain with information from the periphery to mediate central responses to humoral signals and physiological stressors. Circumventricular organs are characterized by the presence of unique populations of non-neuronal cells, such as tanycytes and fenestrated endothelium. However, how these populations are organized within the SFO is not well understood. In this study, we used histological techniques to analyze the anatomical organization of the rat SFO and examined the distribution of neurons, fenestrated and non-fenestrated vasculature, tanycytes, ependymocytes, glia cells, and pericytes within its confines. Our data show that the shell of SFO contains non-fenestrated vasculature, while fenestrated capillaries are restricted to the medial-posterior core region of the SFO and associated with a higher BBB permeability. In contrast to non-fenestrated vessels, fenestrated capillaries are encased in a scaffold created by pericytes and embedded in a network of tanycytic processes. Analysis of c-Fos expression following systemic injections of angiotensin II or hypertonic NaCl reveals distinct neuronal populations responding to these stimuli. Hypertonic NaCl activates ∼13% of SFO neurons located in the shell. Angiotensin II-sensitive neurons represent ∼35% of SFO neurons and their location varies between sexes. Our study provides a comprehensive description of the organization of diverse cellular elements within the SFO, facilitating future investigations in this important brain area.

The calcitonin receptor is the main mediator of LAAMA's body weight lowering effects in male mice

The anorectic action of the pancreatic hormone amylin is mainly mediated through the area postrema (AP). Amylin activates AP neurons using a heterodimeric receptor (AMY) composed of the calcitonin receptor (CTR) and the receptor activity modifying protein (RAMP 1, 2 or 3). The aim of the following experiments is to test the effects of the long acting amylin analogue (LAAMA) in RAMP1/3 knock-out (KO) male mice and in neuronal CTR KO Nestin-Cre^CTR male mice. In vitro, LAAMA exerted an equipotent effect on CTR and AMYs that was maintained across species. Following one week of 45% high fat diet, WT, RAMP1/3 KO and Nestin-Cre^CTR mice were injected daily for one week with vehicle or LAAMA. LAAMA decreased body weight gain in WT and in RAMP1/3 KO mice suggesting that RAMP1/3 are not necessary for LAAMA-induced effects. However, LAAMA was not able to produce any body lowering and anorectic effects in Nestin-Cre^CTR mice. This was accompanied by the absence of any c-Fos signal in the AP opposite to WT control mice. Together, these results suggest that LAAMA's effects are mainly mediated through CTR rather than specific AMY. The study of LAAMA or any amylin receptor agonist in different receptor KO mouse models helps disentangle the underlying mechanisms used by these molecules.

A selective role for receptor activity-modifying proteins in subchronic action of the amylin selective receptor agonist NN1213 compared with salmon calcitonin on body weight and food intake in male mice

The role of receptor activity‐modifying proteins (RAMPs) in modulating the pharmacological effects of an amylin receptor selective agonist (NN1213) or the dual amylin–calcitonin receptor agonist (DACRA), salmon calcitonin (sCT), was tested in three RAMP KO mouse models, RAMP1, RAMP3 and RAMP1/3 KO. Male wild‐type (WT) and knockout (KO) littermate mice were fed a 45% high‐fat diet for 20 weeks prior to the 3‐week treatment period. A decrease in body weight after NN1213 was observed in all WT mice, whereas sCT had no effect. The absence of RAMP1 had no significant effect on NN1213 efficacy, and sCT was still inactive. However, the absence of RAMP3 impeded NN1213 efficacy but improved sCT efficacy. Similar results were observed in RAMP1/3 KO suggesting that the amylin receptor 3 (AMY3 = CTR + RAMP3) is necessary for NN1213's maximal action on body weight and food intake and that the lack of AMY3 allowed sCT to be active. These results suggest that the chronic use of DACRA such as sCT can have unfavourable effect on body weight loss in mice (which differs from the situation in rats), whereas the use of the amylin receptor selective agonist does not. AMY3 seems to play a crucial role in modulating the action of these two compounds, but in opposite directions. The assessment of a long‐term effect of amylin and DACRA in different rodent models is necessary to understand potential physiological beneficial and unfavourable effects on weight loss before its transition to clinical trials.

Salmon Calcitonin Attenuates Some Behavioural Responses to Nicotine in Male Mice

The behavioural responses to nicotine involve appetite-regulatory hormones; however, the effects of the anorexigenic hormone amylin on reward-related behaviours induced by nicotine remain to be established. Previous studies have shown that the amylinergic pathway regulates behavioural responses to alcohol, amphetamine and cocaine. Here, we evaluated the effects of salmon calcitonin (sCT), an amylin and calcitonin receptor (CTR) agonist, on nicotine-induced locomotor stimulation and sensitisation as well as dopamine release in the nucleus accumbens (NAc) shell. Moreover, we investigated the effects of sCT on the acquisition and expression of nicotine-induced reward in the conditioned place preference (CPP) paradigm. Finally, we performed Western Blot experiments in an attempt to identify the levels of the amylin receptor components CTRa, CTRb, and RAMP1 in reward-related areas of mice responding differently to repeated injections of sCT and nicotine in the locomotor sensitisation test. We found that sCT blocked nicotine’s stimulatory and dopamine-releasing effects and prevented its ability to cause locomotor sensitisation. On the other hand, sCT did not alter nicotine-induced acquisition and expression of CPP. Lastly, sCT-nicotine treated mice from the locomotor sensitisation experiment displayed higher levels of total CTR, i.e. CTRa and CTRb together, in the reward-processing laterodorsal tegmental area (LDTg) of the brain compared to mice treated with vehicle-nicotine. Overall, the present data reveal that activation of CTR or/and amylin receptors attenuates certain nicotine-induced behaviours in male mice, further contributing to the understanding of appetite-regulatory peptides in reward regulation.

Interictal amylin levels in chronic migraine patients: A case-control study

BACKGROUND

Recently, amylin and its receptors were found in different structures involved in migraine pathophysiology. Here, we evaluate interictal concentrations of amylin and calcitonin gene-related peptide in peripheral blood as biomarkers for chronic migraine.

METHODS

We prospectively recruited patients with episodic migraine, chronic migraine and healthy controls. Interictal amylin and calcitonin gene-related peptide levels were assessed in blood samples using enzyme linked immunosorbent assay.

RESULTS

We assessed plasma samples from 58 patients with episodic migraine (mean age 37.71 ± 10.47, 87.9% female), 191 with chronic migraine (mean age 46.03 ± 11.93, 95% female), and on 68 healthy controls (mean age 43.58 ± 11.08 years, 86% female). Body mass index was 25.94 ± 4.53 kg/m² for migraine patients and 25.13 ± 4.92 kg/m² for healthy controls (p = 0.0683). Interictal plasma amylin levels were higher in chronic migraine patients (47.1 pg/mL) than in the episodic migraine patients (28.84 pg/mL, p < 0.0001) and healthy controls (24.74 pg/mL, p < 0.0001). Plasma calcitonin gene-related peptide levels were increased (20.01 pg/mL) in chronic migraine patients when compared to healthy controls (11.37 pg/mL, p = 0.0016), but not to episodic migraine patients (18.89 pg/mL, p = 0.4369). Applying a cut-off concentration of 39.68 pg/mL plasma amylin, the sensitivity to differentiate chronic migraine from healthy controls was 57.6% and the specificity was 88.2%. Variables such as age, analgesic overuse, depression, allodynia, use of preventive medication or a history of aura did not influence the plasma concentrations of amylin or calcitonin gene-related peptide.

CONCLUSION

Interictal plasma amylin levels are higher in patients with chronic migraine and may serve as a diagnostic biomarker for chronic migraine.

The Importance of Understanding Amylin Signaling Mechanisms for Therapeutic Development in the Treatment of Alzheimer's Disease

Type II Diabetes (T2D) is a major risk factor for Alzheimer's Disease (AD). These two diseases share several pathological features, including amyloid accumulation, inflammation, oxidative stress, cell death and cognitive decline. The metabolic hormone amylin and amyloid-beta are both amyloids known to self-aggregate in T2D and AD, respectively, and are thought to be the main pathogenic entities in their respective diseases. Furthermore, studies suggest amylin's ability to seed amyloid-beta aggregation, the activation of common signaling cascades in the pancreas and the brain, and the ability of amyloid beta to signal through amylin receptors (AMYR), at least in vitro. However, paradoxically, non-aggregating forms of amylin such as pramlintide are given to treat T2D and functional and neuroprotective benefits of amylin and pramlintide administration have been reported in AD transgenic mice. These paradoxical results beget a deeper study of the complex nature of amylin's signaling through the several AMYR subtypes and other receptors associated with amylin effects to be able to fully understand its potential role in mediating AD development and/or prevention. The goal of this review is to provide such critical insight to begin to elucidate how the complex nature of this hormone's signaling may explain its equally complex relationship with T2D and mechanisms of AD pathogenesis.

Thirst recruits phasic dopamine signaling through subfornical organ neurons

Thirst is a highly potent drive that motivates organisms to seek out and consume balance-restoring stimuli. The detection of dehydration is well understood and involves signals of peripheral origin and the sampling of internal milieu by first order homeostatic neurons within the lamina terminalis-particularly glutamatergic neurons of the subfornical organ expressing CaMKIIa (SFO^CaMKIIa). However, it remains unknown whether mesolimbic dopamine pathways that are critical for motivation and reinforcement integrate information from these "early" dehydration signals. We used in vivo fiber photometry in the ventral tegmental area and measured phasic dopamine responses to a water-predictive cue. Thirst, but not hunger, potentiated the phasic dopamine response to the water cue. In euvolemic rats, the dipsogenic hormone angiotensin II, but not the orexigenic hormone ghrelin, potentiated the dopamine response similarly to that observed in water-deprived rats. Chemogenetic manipulations of SFO^CaMKIIa revealed bidirectional control of phasic dopamine signaling during cued water reward. Taking advantage of within-subject designs, we found predictive relationships between changes in cue-evoked dopamine response and changes in behavioral responses-supporting a role for dopamine in motivation induced by homeostatic need. Collectively, we reveal a putative mechanism for the invigoration of goal-directed behavior: internal milieu communicates to first order, need state-selective circuits to potentiate the mesolimbic dopamine system's response to cues predictive of restorative stimuli.

Amylin brain circuitry

Amylin is a peptide hormone that is mainly known to be produced by pancreatic β-cells in response to a meal but amylin is also produced by brain cells in discrete brain areas albeit in a lesser amount. Amylin receptor (AMY) is composed of the calcitonin core-receptor (CTR) and one of the 3 receptor activity modifying protein (RAMP), thus forming AMY1-3; RAMP enhances amylin binding properties to the CTR. However, amylin receptor agonist such as salmon calcitonin is able to bind CTR alone. Peripheral amylin's main binding site is located in the area postrema (AP) which then propagate the signal to the nucleus of the solitary tract and lateral parabrachial nucleus (LPBN) and it is then transmitted to the forebrain areas such as central amygdala and bed nucleus of the stria terminalis. Amylin's activation of these different brain areas mediates eating and other metabolic pathways controlling energy expenditure and glucose homeostasis. Peripheral amylin can also bind in the arcuate nucleus of the hypothalamus where it acts independently of the AP to activate POMC and NPY neurons. Amylin activation of NPY neurons has been shown to be transmitted to LPBN neurons to act on eating while amylin POMC signaling affects energy expenditure and locomotor activity. While a large amount of experiments have already been conducted, future studies will have to further investigate how amylin is taken up by forebrain areas and deepen our understanding of amylin action on peripheral metabolism.

Noradrenaline signaling in the LPBN mediates amylin's and salmon calcitonin's hypophagic effect in male rats

The LPBN (lateral parabrachial nucleus) plays an important role in feeding control. CGRP (calcitonin gene-related peptide) LPBN neurons activation mediates the anorectic effects of different gut-derived peptides, including amylin. Amylin and its long acting analog sCT (salmon calcitonin) exert their anorectic actions primarily by directly activating neurons located in the area postrema (AP). A large proportion of projections from the AP and the adjacent nucleus of the solitary tractNTS to the LPBN, are noradrenergic (NA), and amylin-activated NA^AP neurons are critical in mediating amylin's hypophagic effects. Here, we determine the functional role of NA^AP amylin activated neurons to activate CGRP and non-CGRP LPBN neurons. To this end, NA was specifically depleted in the rat LPBN through a stereotaxic microinfusion of 6-OHDA, a neurotoxic agent that destroys NA terminals. While amylin (50 μg/kg) and sCT (5 μg/kg) reduced eating in sham-lesioned rats, no reduction in feeding occurred in NA-depleted animals. Further, the amylin-induced c-Fos response in the LPBN and c-Fos/CGRP colocalization were reduced in NA-depleted animals compared to controls. We conclude that AP → LPBN NA signaling, through the activation of LPBN CGRP neurons, mediates part of amylin's hypophagic effect.

Systemic and Central Amylin, Amylin Receptor Signaling, and Their Physiological and Pathophysiological Roles in Metabolism

This article in the Neural and Endocrine Section of Comprehensive Physiology discusses the physiology and pathophysiology of the pancreatic hormone amylin. Shortly after its discovery in 1986, amylin has been shown to reduce food intake as a satiation signal to limit meal size. Amylin also affects food reward, sensitizes the brain to the catabolic actions of leptin, and may also play a prominent role in the development of certain brain areas that are involved in metabolic control. Amylin may act at different sites in the brain in addition to the area postrema (AP) in the caudal hindbrain. In particular, the sensitizing effect of amylin on leptin action may depend on a direct interaction in the hypothalamus. The concept of central pathways mediating amylin action became more complex after the discovery that amylin is also synthesized in certain hypothalamic areas but the interaction between central and peripheral amylin signaling remains currently unexplored. Amylin may also play a dominant pathophysiological role that is associated with the aggregation of monomeric amylin into larger, cytotoxic molecular entities. This aggregation in certain species may contribute to the development of type 2 diabetes mellitus but also cardiovascular disease. Amylin receptor pharmacology is complex because several distinct amylin receptor subtypes have been described, because other neuropeptides [e.g., calcitonin gene-related peptide (CGRP)] can also bind to amylin receptors, and because some components of the functional amylin receptor are also used for other G-protein coupled receptor (GPCR) systems. © 2020 American Physiological Society. Compr Physiol 10:811-837, 2020.

Late Pathomorphological Features of the Endocrine Pancreas in Patients With Type 2 Diabetes Mellitus

Introduction Islet amyloid polypeptide (IAPP) amyloidosis is a pathologic alteration of the pancreas, represented by abnormal accumulation of amylin in the interstitial tissue. Amylin is a neuroendocrine hormone, co-secreted with insulin by beta cells and participating in downstream regulation of postprandial glycemia. This report aims to examine IAPP amyloidosis as a late consequence of poor control of blood glucose levels in patients with type 2 diabetes mellitus (T2DM) who have been referred for autopsy. Materials and methods A total of 34 consecutive autopsies performed at the St. Marina University Hospital, Varna, Bulgaria, carried out by a single pathologist were included in the study. Samples from the tail of the pancreas were obtained to evaluate the state of the changes and were analyzed together with the specific organ changes associated with T2DM, as well as the medical documentation of the patients. Results Of the 34 autopsies, 10 cases (six females and four males) were included in the study, seven of whom had a medical history of T2D. The average age was 65.7 years (range 50 to 85 years). In all of the cases, morphological features of fibrosis and lipomatosis were present, with one of the patients having signs of pancreatic amyloidosis - Congo red positive deposition of pink, amorphous material in the extracellular matrix. Conclusion The described pathological alterations in all of the cases illustrate the progressing impairment of the structure of the pancreas, especially beta cells dysfunction in late stages of T2D, and highlight IAPP amyloidosis as the cause of irreversible damage of the isles of Langerhans and beta cell death.

Amylin/Calcitonin Receptor-Mediated Signaling in POMC Neurons Influences Energy Balance and Locomotor Activity in Chow-Fed Male Mice

Amylin, a pancreatic hormone and neuropeptide, acts principally in the hindbrain to decrease food intake and has recently been shown to act as a neurotrophic factor to control the development of area postrema → nucleus of the solitary tract and arcuate hypothalamic nucleus → paraventricular nucleus axonal fiber outgrowth. Amylin is also able to activate ERK signaling specifically in POMC neurons independently of leptin. For investigation of the physiological role of amylin signaling in POMC neurons, the core component of the amylin receptor, calcitonin receptor (CTR), was depleted from POMC neurons using an inducible mouse model. The loss of CTR in POMC neurons leads to increased body weight gain, increased adiposity, and glucose intolerance in male knockout mice, characterized by decreased energy expenditure (EE) and decreased expression of uncoupling protein 1 (UCP1) in brown adipose tissue. Furthermore, a decreased spontaneous locomotor activity and absent thermogenic reaction to the application of the amylin receptor agonist were observed in male and female mice. Together, these results show a significant physiological impact of amylin/calcitonin signaling in CTR-POMC neurons on energy metabolism and demonstrate the need for sex-specific approaches in obesity research and potentially treatment.

Palatable food access impacts expression of amylin receptor components in the mesocorticolimbic system

NEW FINDINGS

What is the central question of this study? We tested whether intra-nucleus accumbens core amylin receptor (AmyR) activation suppresses feeding and evaluated whether intake of palatable food influences mesocorticolimbic AmyR expression. What is the main finding and its importance? Intra-nucleus accumbens core AmyR activation reduces food intake in some dietary conditions. We showed that all components of the AmyR are expressed in the prefrontal cortex and central nucleus of the amygdala and demonstrated that access to fat impacts AmyR expression in these and other mesocorticolimbic nuclei. These results suggest that the intake of palatable food might alter amylin signalling in the brain and shed further light onto potential sites of action for amylin.

ABSTRACT

Amylin is a pancreas- and brain-derived peptide that acts within the CNS to promote negative energy balance. However, our understanding of the CNS sites of action for amylin remains incomplete. Here, we investigate the effect of amylin receptor (AmyR) activation in the nucleus accumbens core (NAcC) on the intake of bland and palatable foods. Intra-NAcC injection of the AmyR agonist salmon calcitonin or amylin itself in male chow-fed rats had no effect on food intake, meal size or number of meals. However, in chow-fed rats with access to fat solution, although fat intake was not affected by intra-NAcC AmyR activation, subsequent chow intake was suppressed. Given that mesolimbic AmyR activation suppresses energy intake in rats with access to fat solution, we tested whether fat access changes AmyR expression in key mesocorticolimbic nuclei. Fat exposure did not affect NAcC AmyR expression, whereas in the accumbens shell, expression of receptor activity modifying protein (RAMP) 3 was significantly reduced in fat-consuming rats. We show that all components of AmyRs are expressed in the medial prefrontal cortex and central nucleus of the amygdala; fat access significantly reduced expression of calcitonin receptor-A in the central nucleus of the amygdala and RAMP2 in the medial prefrontal cortex. Taken together, these results indicate that intra-NAcC AmyR activation can suppress energy intake and, furthermore, suggest that AmyR signalling in a broader range of mesocorticolimbic sites might have a role in mediating the effects of amylin on food intake and body weight.

Relation between serum amylin level and epilepsy

Background

Epilepsy is a neurological disorder characterized by convulsions. Identification of biological pathways underlying epilepsy and novel genes may shed light on the pathogenesis of epilepsy as well as new targets for treatment.

Objectives

Amylin is cosecreted with insulin from the pancreatic β-cells in a pulsatile manner as a response to nutrient stimuli. In vitro studies have shown the neurotoxicity potential of amylin. We aimed to investigate serum amylin levels between epilepsy patients and a healthy control group.

Subjects and methods

For this study, 45 patients with epilepsy and 60 healthy controls were enrolled. Routine blood analysis and electroencephalography scan were performed for all participants. Five cc venous blood sample was collected from each participant. Sera were isolated and stored at − 80 °C until the time of amylin analysis with the enzyme-linked immunosorbent assay.

Results

Gender distribution of the two groups was as follows: 44.4% males and 55.6% females among epileptic patients and 53.3% males and 46.7% females for control subjects.

Body mass index was 23.09 ± 3.99 kg/m2 for epileptic patients and 26.29 ± 4.83 kg/m2 for controls, with a statistically significantly higher body mass index in control subjects (p ˂ 0.001). With regard to serum amylin levels, a statistically significant difference was observed between the two groups (p ˂ 0.001). The median serum amylin concentration was 226.62 ng/ml (69.49–6961.19 (min–max)) for epileptic patients and 103.66 ng/ml (37.42–607.11 (min–max)) for controls (p ˂ 0.001).

Conclusion

In the present study, a significant difference was observed between patient and control groups in serum amylin concentrations, which were considerably higher in epileptic patients.

Salmon calcitonin distributes into the arcuate nucleus to a subset of NPY neurons in mice

The amylin receptor (AMY) and calcitonin receptor (CTR) agonists induce acute suppression of food intake in rodents by binding to receptors in the area postrema (AP) and potentially by targeting arcuate (ARC) neurons directly. Salmon calcitonin (sCT) induces more potent, longer lasting anorectic effects compared to amylin. We thus aimed to investigate whether AMY/CTR agonists target key neuronal populations in the ARC, and whether differing brain distribution patterns could mediate the observed differences in efficacy with sCT and amylin treatment. Brains were examined by whole brain 3D imaging and confocal microscopy following subcutaneous administration of fluorescently labelled peptides to mice. We found that sCT, but not amylin, internalizes into a subset of ARC NPY neurons, along with an unknown subset of ARC, AP and dorsal vagal motor nucleus cells. ARC POMC neurons were not targeted. Furthermore, amylin and sCT displayed similar distribution patterns binding to receptors in the AP, the organum vasculosum of the lamina terminalis (OVLT) and the ARC. Amylin distributed within the median eminence with only specs of sCT being present in this region, however amylin was only detectable 10 minutes after injection while sCT displayed a residence time of up to 2 hours post injection. We conclude that AMY/CTR agonists bind to receptors in a subset of ARC NPY neurons and in circumventricular organs. Furthermore, the more sustained and greater anorectic efficacy of sCT compared to rat amylin is not attributable to differences in brain distribution patterns but may more likely be explained by greater potency at both the CTR and AMY.

Effects of sub-chronic amylin receptor activation on alcohol-induced locomotor stimulation and monoamine levels in mice

RATIONALE

Amylin receptors consist of the calcitonin receptor (CTR) and one of three receptor activity-modifying proteins (RAMPs). The identification of amylin receptors in areas processing reward, namely laterodorsal tegmental area (LDTg), ventral tegmental area (VTA), and nucleus accumbens (NAc), has attributed them a role as reward regulators. Indeed, acute activation of amylin receptors by the amylin receptor agonist salmon calcitonin (sCT) attenuates alcohol-induced behaviours in rodents.

OBJECTIVES

The effects of long-term administration of sCT on alcohol-related behaviours and the molecular mechanisms underlying these processes are not yet elucidated. To fill this knowledge gap, we investigated the effects of sub-chronic sCT treatment on the locomotor stimulatory responses to alcohol in mice and the molecular pathways involved.

METHODS

We assessed the behavioural effects of sub-chronic sCT treatment by means of locomotor activity experiments in mice. We used western blot to identify changes of the CTR levels and ex vivo biochemical analysis to detect changes in monoamines and their metabolites.

RESULTS

After discontinuation for 5 days of sCT treatment, alcohol did not induce locomotor stimulation in mice pre-treated with sCT when compared with vehicle, without altering secondary behavioural parameters of the locomotor activity experiment or the protein levels of the CTR in reward-related areas in the same set of animals. Moreover, repeated sCT treatment altered monoaminergic neurotransmission in various brain areas, including increased serotonin and decreased dopamine turnover in the VTA. Lastly, we identified a differential effect of repeated sCT and acute alcohol administration on alcohol-induced locomotion in mice, where sCT initially attenuated and later increased this alcohol response. It was further found that this treatment combination did not affect secondary behavioural parameters measured in this locomotor activity experiments.

CONCLUSIONS

These data suggest that sub-chronic sCT treatment differentially alters the ability of alcohol to cause locomotor stimulation, possibly through molecular mechanisms involving various neurotransmitter systems and not the CTR levels per se.

Fluorescently-labeled fremanezumab is distributed to sensory and autonomic ganglia and the dura but not to the brain of rats with uncompromised blood brain barrier

Background

The presence of calcitonin gene-related peptide and its receptors in multiple brain areas and peripheral tissues previously implicated in migraine initiation and its many associated symptoms raises the possibility that humanized monoclonal anti-calcitonin gene-related peptide antibodies (CGRP-mAbs) can prevent migraine by modulating neuronal behavior inside and outside the brain. Critical to our ability to conduct a fair discussion over the mechanisms of action of CGRP-mAbs in migraine prevention is data generation that determines which of the many possible peripheral and central sites are accessible to these antibodies – a question raised frequently due to their large size.

Material and methods

Rats with uncompromised and compromised blood-brain barrier (BBB) were injected with Alexa Fluor 594-conjugated fremanezumab (Frema594), sacrificed 4 h or 7 d later, and relevant tissues were examined for the presence of Frema594.

Results

In rats with uncompromised BBB, Frema594 was similarly observed at 4 h and 7 d in the dura, dural blood vessels, trigeminal ganglion, C2 dorsal root ganglion, the parasympathetic sphenopalatine ganglion and the sympathetic superior cervical ganglion but not in the spinal trigeminal nucleus, thalamus, hypothalamus or cortex. In rats with compromised BBB, Frema594 was detected in the cortex (100 µm surrounding the compromised BBB site) 4 h but not 7 d after injections.

Discussion

Our inability to detect fluorescent (CGRP-mAbs) in the brain supports the conclusion that CGRP-mAbs prevent the headache phase of migraine by acting mostly, if not exclusively, outside the brain as the amount of CGRP-mAbs that enters the brain (if any) is too small to be physiologically meaningful.

Amylin and Leptin interaction: Role During Pregnancy, Lactation and Neonatal Development

Amylin is co-secreted with insulin by pancreatic β-cells in response to a meal and produced by neurons in discrete hypothalamic brain areas. Leptin is proportionally secreted by the adipose tissue. Both hormones control food intake and energy homeostasis post-weaning in rodents. While amylin's main site of action is located in the area postrema (AP) and leptin's is located in the mediobasal hypothalamus, both hormones can also influence the other's signaling pathway; amylin has been shown enhance hypothalamic leptin signaling, and amylin signaling in the AP may rely on functional leptin receptors to modulate its effects. These two hormones also play major roles during other life periods. During pregnancy, leptin levels rise as a result of an increase in fat depot resulting in gestational leptin-resistance to prepare the maternal body for the metabolic needs during fetal development. The role of amylin is far less studied during pregnancy and lactation, though amylin levels seem to be elevated during pregnancy relative to insulin. Whether amylin and leptin interact during pregnancy and lactation remains to be assessed. Lastly, during brain development, amylin and leptin are major regulators of cell birth during embryogenesis and act as neurotrophic factors in the neonatal period. This review will highlight the role of amylin and leptin, and their possible interaction, during these dynamic time periods of pregnancy, lactation, and early development.

An amylin analogue attenuates alcohol-related behaviours in various animal models of alcohol use disorder

Recent findings have identified salmon calcitonin (sCT), an amylin receptor agonist and analogue of endogenous amylin, as a potential regulator of alcohol-induced activation of the mesolimbic dopamine system and alcohol consumption. Providing that the role of amylin signalling in alcohol-related behaviours remains unknown, the present experiments investigate the effect of sCT on these behaviours and the mechanisms involved. We showed that repeated sCT administration decreased alcohol and food intake in outbred rats. Moreover, single administration of the potent amylin receptor antagonist, AC187, increased short-term alcohol intake in outbred alcohol-consuming rats, but did not affect food intake. Acute administration of sCT prevented relapse-like drinking in the "alcohol deprivation effect" model in outbred alcohol-experienced rats. Additionally, acute sCT administration reduced operant oral alcohol self-administration (under the fixed ratio 4 schedule of reinforcement) in selectively bred Sardinian alcohol-preferring rats, while it did not alter operant self-administration (under the progressive ratio schedule of reinforcement) of a highly palatable chocolate-flavoured beverage in outbred rats. Lastly, we identified differential amylin receptor expression in high compared to low alcohol-consuming rats, as reflected by decreased calcitonin receptor and increased receptor activity modifying protein 1 expression in the nucleus accumbens (NAc) of high consumers. Collectively, our data suggest that amylin signalling, especially in the NAc, may contribute to reduction of various alcohol-related behaviours.

Activation of amylin receptors attenuates alcohol-mediated behaviours in rodents

Alcohol expresses its reinforcing properties by activating areas of the mesolimbic dopamine system, which consists of dopaminergic neurons projecting from the ventral tegmental area to the nucleus accumbens. The findings that reward induced by food and addictive drugs involve common mechanisms raise the possibility that gut-brain hormones, which control appetite, such as amylin, could be involved in reward regulation. Amylin decreases food intake, and despite its implication in the regulation of natural rewards, tenuous evidence support amylinergic mediation of artificial rewards, such as alcohol. Therefore, the present experiments were designed to investigate the effect of salmon calcitonin (sCT), an amylin receptor agonist and analogue of endogenous amylin, on various alcohol-related behaviours in rodents. We showed that acute sCT administration attenuated the established effects of alcohol on the mesolimbic dopamine system, particularly alcohol-induced locomotor stimulation and accumbal dopamine release. Using the conditioned place preference model, we demonstrated that repeated sCT administration prevented the expression of alcohol's rewarding properties and that acute sCT administration blocked the reward-dependent memory consolidation. In addition, sCT pre-treatment attenuated alcohol intake in low alcohol-consuming rats, with a more evident decrease in high alcohol consumers in the intermittent alcohol access model. Lastly, sCT did not alter peanut butter intake, blood alcohol concentration and plasma corticosterone levels in mice. Taken together, the present data support that amylin signalling is involved in the expression of alcohol reinforcement and that amylin receptor agonists could be considered for the treatment of alcohol use disorder in humans.

A contemporary biological pathway of islet amyloid polypeptide for the management of diabetic dementia

Major challenges of dealing elder patients with diabetes mellitus (DM) are the individualization of consideration in persons with various comorbid types of conditions. In spite of the fact that microvascular and macrovascular problems associated with DM are well documented, there is only a few numbers of reports viewing different conditions, for example, cognitive dysfunction. Cognitive dysfunction is of specific significance due to its effect on self-care and quality of life. All in all, the etiology of cognitive dysfunction in the maturing populace is probably going to be the grouping of ischemic and degenerative pathology. It is likewise trusted that Hyperglycemia is engaged with the system of DM-related cognitive dysfunction. At present, it isn't certain in the case of enhancing glycemic control or utilizing therapeutic agents can enhance the risk of cognitive decay. Amylin was later characterized as an amyloidogenic peptide, confined from a beta cell tumor and called islet amyloid polypeptide (IAPP), and after that, amylin. Conversely, we investigate the beneficial role and hypothesizing the mechanism of amylin related expanding the level and activation of CGRP receptor to enhance the cognition declination amid diabetic dementia.

From sensory circumventricular organs to cerebral cortex: Neural pathways controlling thirst and hunger

Much progress has been made during the past 30 years with respect to elucidating the neural and endocrine pathways by which bodily needs for water and energy are brought to conscious awareness through the generation of thirst and hunger. One way that circulating hormones influence thirst and hunger is by acting on neurones within sensory circumventricular organs (CVOs). This is possible because the subfornical organ and organum vasculosum of the lamina terminalis (OVLT), the sensory CVOs in the forebrain, and the area postrema in the hindbrain lack a normal blood-brain barrier such that neurones within them are exposed to blood-borne agents. The neural signals generated by hormonal action in these sensory CVOs are relayed to several sites in the cerebral cortex to stimulate or inhibit thirst or hunger. The subfornical organ and OVLT respond to circulating angiotensin II, relaxin and hypertonicity to drive thirst-related neural pathways, whereas circulating amylin, leptin and possibly glucagon-like peptide-1 act at the area postrema to influence neural pathways inhibiting food intake. As a result of investigations using functional brain imaging techniques, the insula and anterior cingulate cortex, as well as several other cortical sites, have been implicated in the conscious perception of thirst and hunger in humans. Viral tracing techniques show that the anterior cingulate cortex and insula receive neural inputs from thirst-related neurones in the subfornical organ and OVLT, with hunger-related neurones in the area postrema having polysynaptic efferent connections to these cortical regions. For thirst, initially, the median preoptic nucleus and, subsequently, the thalamic paraventricular nucleus and lateral hypothalamus have been identified as likely sites of synaptic links in pathways from the subfornical organ and OVLT to the cortex. The challenge remains to identify the links in the neural pathways that relay signals originating in sensory CVOs to cortical sites subserving either thirst or hunger.

Role and Cytotoxicity of Amylin and Protection of Pancreatic Islet β-Cells from Amylin Cytotoxicity

Amylin, (or islet amyloid polypeptide; IAPP), a 37-amino acid peptide hormone, is released in response to nutrients, including glucose, lipids or amino acids. Amylin is co-stored and co-secreted with insulin by pancreatic islet β-cells. Amylin inhibits food intake, delays gastric emptying, and decreases blood glucose levels, leading to the reduction of body weight. Therefore, amylin as well as insulin play important roles in controlling the level of blood glucose. However, human amylin aggregates and human amylin oligomers cause membrane disruption, endoplasmic reticulum (ER) stress and mitochondrial damage. Since cytotoxicity of human amylin oligomers to pancreatic islet β-cells can lead to diabetes, the protection of pancreatic islet β cells from cytotoxic amylin is crucial. Human amylin oligomers also inhibit autophagy, although autophagy can function to remove amylin aggregates and damaged organelles. Small molecules, including β-sheet breaker peptides, chemical chaperones, and foldamers, inhibit and disaggregate amyloid formed by human amylin, suggesting the possible use of these small molecules in the treatment of diabetes. In this review, we summarize recent findings regarding the role and cytotoxicity of amylin and the protection of pancreatic islet β-cells from cytotoxicity of amylin.

Molecular Signature for Receptor Engagement in the Metabolic Peptide Hormone Amylin

The pancreatic peptide hormone, amylin, plays a critical role in the control of appetite, and synergizes with other key metabolic hormones such as glucagon-like peptide 1 (GLP-1). There is opportunity to develop potent and long-acting analogues of amylin or hybrids between these and GLP-1 mimetics for treating obesity. To achieve this, interrogation of how the 37 amino acid amylin peptide engages with its complex receptor system is required. We synthesized an extensive library of peptides to profile the human amylin sequence, determining the role of its disulfide loop, amidated C-terminus and receptor "capture" and "activation" regions in receptor signaling. We profiled four signaling pathways with different ligands at multiple receptor subtypes, in addition to exploring selectivity determinants between related receptors. Distinct roles for peptide subregions in receptor binding and activation were identified, resulting in peptides with greater activity than the native sequence. Enhanced peptide activity was preserved in the brainstem, the major biological target for amylin. Interpretation of our data using full-length active receptor models supported by molecular dynamics, metadynamics, and supervised molecular dynamics simulations guided the synthesis of a potent dual agonist of GLP-1 and amylin receptors. The data offer new insights into the function of peptide amidation, how allostery drives peptide-receptor interactions, and provide a valuable resource for the development of novel amylin agonists for treating diabetes and obesity.

The Link between Type 2 Diabetes and Neurodegeneration: Roles for Amyloid-β, Amylin, and Tau Proteins

A wealth of evidence indicates a strong link between type 2 diabetes (T2D) and neurodegenerative diseases such as Alzheimer's disease (AD). Although the precise mechanism remains unclear, T2D can exacerbate neurodegenerative processes. Brain atrophy, reduced cerebral glucose metabolism, and central nervous system insulin resistance are features of both AD and T2D. The T2D phenotype (glucose dyshomeostasis, insulin resistance, impaired insulin signaling) also promotes AD pathology, namely accumulation of amyloid-β (Aβ) and hyperphosphorylated tau and can induce other aspects of neuronal degeneration including inflammatory and oxidative processes. Aβ and hyperphosphorylated tau may also have roles in pancreatic β-cell dysfunction and in reducing insulin sensitivity and glucose uptake by peripheral tissues such as liver, skeletal muscle, and adipose tissue. This suggests a role for these AD-related proteins in promoting T2D. The accumulation of the islet amyloid polypeptide (IAPP, or amylin) within islet β-cells is a major pathological feature of the pancreas in patients with chronic T2D. Co-secreted with insulin, amylin accumulates over time and contributes to β-cell toxicity, ultimately leading to reduced insulin secretion and onset of overt (insulin dependent) diabetes. Recent evidence also suggests that this protein accumulates in the brain of AD patients and may interact with Aβ to exacerbate the neurodegenerative process. In this review, we highlight evidence indicating T2D in promoting Aβ and tau mediated neurodegeneration and the potential contributions of Aβ and tau in promoting a diabetic phenotype that could further exacerbate neurodegeneration. We also discuss underlying mechanisms by which amylin can contribute to the neurodegenerative processes.

Molecular studies of CGRP and the CGRP family of peptides in the central nervous system

BACKGROUND

Calcitonin gene-related peptide is an important target for migraine and other painful neurovascular conditions. Understanding the normal biological functions of calcitonin gene-related peptide is critical to understand the mechanisms of calcitonin gene-related peptide-blocking therapies as well as engineering improvements to these medications. Calcitonin gene-related peptide is closely related to other peptides in the calcitonin gene-related peptide family of peptides, including amylin. Relatedness in peptide sequence and in receptor biology makes it difficult to tease apart the contributions that each peptide and receptor makes to physiological processes and to disorders.

SUMMARY

The focus of this review is the expression of calcitonin gene-related peptide, related peptides and their receptors in the central nervous system. Calcitonin gene-related peptide is expressed throughout the nervous system, whereas amylin and adrenomedullin have only limited expression at discrete sites in the brain. The components of two receptors that respond to calcitonin gene-related peptide, the calcitonin gene-related peptide receptor (calcitonin receptor-like receptor with receptor activity-modifying protein 1) and the AMY₁ receptor (calcitonin receptor with receptor activity-modifying protein 1), are expressed throughout the nervous system. Understanding expression of the peptides and their receptors lays the foundation for more deeply understanding their physiology, pathophysiology and therapeutic use.

Co-expression of the calcitonin receptor gene in the hypothalamic kisspeptin neurons in female rats

Purpose

Hypothalamic kisspeptin neurons are considered to play a critical role in regulating mammalian reproduction and integrating humoral and neuronal inputs that control gonadotropin‐releasing hormone (GnRH)/gonadotropin release. The present study aimed to investigate the upstream regulator candidates for kisspeptin neurons.

Methods

Visualized kisspeptin neurons that were taken from the arcuate nucleus (ARC) of Kiss1‐tdTomato rats were subjected to next‐generation sequencing (NGS) analysis. In situ hybridization (ISH) for the calcitonin receptor gene (Calcr) was performed throughout the whole forebrain of ovariectomized wild‐type female rats that had been implanted with a negative feedback level of estrogen, because the Calcr expression was evident in the ARC kisspeptin neurons from the NGS analysis. Then, a double ISH was performed for the Calcr and kisspeptin gene (Kiss1) in the brain regions, containing either the anteroventral periventricular nucleus (AVPV) or ARC of the female rats.

Results

The NGS analysis revealed that the Calcr was highly expressed in the ARC kisspeptin neurons. It was found that the Calcr was co‐expressed in 12% and 22% of the Kiss1‐expressing cells in the ARC and AVPV, respectively.

Conclusion

The present study suggests that calcitonin receptor signaling could be involved in the regulation of reproductive function through the direct control of the ARC and/or AVPV kisspeptin neurons, and then GnRH/gonadotropin release.

Parallels and Overlap: The Integration of Homeostatic Signals by Mesolimbic Dopamine Neurons

Motivated behaviors are often initiated in response to perturbations of homeostasis. Indeed, animals and humans have fundamental drives to procure (appetitive behaviors) and eventually ingest (consummatory behaviors) substances based on deficits in body fluid (e.g., thirst) and energy balance (e.g., hunger). Consumption, in turn, reinforces motivated behavior and is therefore considered rewarding. Over the years, the constructs of homeostatic (within the purview of the hypothalamus) and reward (within the purview of mesolimbic circuitry) have been used to describe need-based vs. need-free consumption. However, many experiments have demonstrated that mesolimbic circuits and "higher-order" brain regions are also profoundly influenced by changes to physiological state, which in turn generate behaviors that are poised to maintain homeostasis. Mesolimbic pathways, particularly dopamine neurons of the ventral tegmental area (VTA) and their projections to nucleus accumbens (NAc), can be robustly modulated by a variety of energy balance signals, including post-ingestive feedback relaying nutrient content and hormonal signals reflecting hunger and satiety. Moreover, physiological states can also impact VTA-NAc responses to non-nutritive rewards, such as drugs of abuse. Coupled with recent evidence showing hypothalamic structures are modulated in anticipation of replenished need, classic boundaries between circuits that convey perturbations in homeostasis and those that drive motivated behavior are being questioned. In the current review, we examine data that have revealed the importance of mesolimbic dopamine neurons and their downstream pathways as a dynamic neurobiological mechanism that provides an interface between physiological state, perturbations to homeostasis, and reward-seeking behaviors.

Amylin Acts in the Lateral Dorsal Tegmental Nucleus to Regulate Energy Balance Through Gamma-Aminobutyric Acid Signaling

BACKGROUND

The pancreatic- and brain-derived hormone amylin promotes negative energy balance and is receiving increasing attention as a promising obesity therapeutic. However, the neurobiological substrates mediating amylin's effects are not fully characterized. We postulated that amylin acts in the lateral dorsal tegmental nucleus (LDTg), an understudied neural processing hub for reward and homeostatic feeding signals.

METHODS

We used immunohistochemical and quantitative polymerase chain reaction analyses to examine expression of the amylin receptor complex in rat LDTg tissue. Behavioral experiments were performed to examine the mechanisms underlying the hypophagic effects of amylin receptor activation in the LDTg.

RESULTS

Immunohistochemical and quantitative polymerase chain reaction analyses show expression of the amylin receptor complex in the LDTg. Activation of LDTg amylin receptors by the agonist salmon calcitonin dose-dependently reduces body weight, food intake, and motivated feeding behaviors. Acute pharmacological studies and longer-term adeno-associated viral knockdown experiments indicate that LDTg amylin receptor signaling is physiologically and potentially preclinically relevant for energy balance control. Finally, immunohistochemical data indicate that LDTg amylin receptors are expressed on gamma-aminobutyric acidergic neurons, and behavioral results suggest that local gamma-aminobutyric acid receptor signaling mediates the hypophagia after LDTg amylin receptor activation.

CONCLUSIONS

These findings identify the LDTg as a novel nucleus with therapeutic potential in mediating amylin's effects on energy balance through gamma-aminobutyric acid receptor signaling.

Amylin - Its role in the homeostatic and hedonic control of eating and recent developments of amylin analogs to treat obesity

BACKGROUND

Amylin is a pancreatic β-cell hormone that produces effects in several different organ systems. One of its best-characterized effects is the reduction in eating and body weight seen in preclinical and clinical studies. Amylin activates specific receptors, a portion of which it shares with calcitonin gene-related peptide (CGRP). Amylin's role in the control of energy metabolism relates to its satiating effect, but recent data indicate that amylin may also affect hedonic aspects in the control of eating, including a reduction of the rewarding value of food. Recently, several amylin-based peptides have been characterized. Pramlintide (Symlin^®) is currently the only one being used clinically to treat type 1 and type 2 diabetes. However other amylin analogs with improved pharmacokinetic properties are being considered as anti-obesity treatment strategies. Several other studies in obesity have shown that amylin agonists could also be useful for weight loss, especially in combination with other agents.

SCOPE OF REVIEW

This review will briefly summarize amylin physiology and pharmacology and then focus on amylin's role in food reward and the effects of amylin analogs in pre-clinical testing for anti-obesity drugs.

CONCLUSION

We propose here that the effects of amylin may be homeostatic and hedonic in nature.