[Show abstract][Hide abstract] ABSTRACT: The amygdala is essential for generating emotional-affective behaviors. It consists of several nuclei with highly selective, elaborate functions. In particular, the central extended amygdala, consisting of the central amygdala (CEA) and the bed nucleus of the stria terminalis (BNST) is an essential component actively controlling efferent connections to downstream effectors like hypothalamus and brain stem. Both, CEA and BNST contain high amounts of different neuropeptides that significantly contribute to synaptic transmission. Among these, neuropeptide Y (NPY) has emerged as an important anxiolytic and fear-reducing neuromodulator. Here, we characterized the expression, connectivity and electrophysiological function of NPY and Y2 receptors within the CEA. We identified several NPY-expressing neuronal populations, including somatostatin- and calretinin-expressing neurons. Furthermore, in the main intercalated nucleus, NPY is expressed primarily in dopamine D1 receptor-expressing neurons but also in interspersed somatostatin-expressing neurons. Interestingly, NPY neurons did not co-localize with the Y2 receptor. Retrograde tract tracing experiments revealed that NPY neurons reciprocally connect the CEA and BNST. Functionally, the Y2 receptor agonist PYY3-36, reduced both, inhibitory as well as excitatory synaptic transmission in the centromedial amygdala (CEm). However, we also provide evidence that lack of NPY or Y2 receptors results in increased GABA release specifically at inhibitory synapses in the CEm. Taken together, our findings suggest that NPY expressed by distinct populations of neurons can modulate afferent and efferent projections of the CEA via presynaptic Y2 receptors located at inhibitory and excitatory synapses.
Brain Structure and Function 09/2015; DOI:10.1007/s00429-015-1107-7 · 5.62 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The TGF-b superfamily cytokine MIC-1/GDF15 circulates in the blood of healthy humans. Its levels rise substantially in cancer and other diseases and this may sometimes lead to development of an anorexia/cachexia syndrome. This is mediated by a direct action of MIC-1/GDF15 on feeding centres in the hypothalamus and brainstem. More recent studies in germline gene deleted mice also suggest that this cytokine may play a role in physiological regulation of energy homeostasis. To further characterize the role of MIC-1/GDF15 in physiological regulation of energy homeostasis in man, we have examined diurnal and food associated variation in serum levels and whether variation in circulating levels relate to BMI in human monozygotic twin pairs. We found that the within twin pair differences in serum MIC-1/GDF15 levels were significantly correlated with within twin pair differences in BMI, suggesting a role for MIC-1/GDF15 in the regulation of energy balance in man. MIC-1/GDF15 serum levels altered slightly in response to a meal, but comparison with variation its serum levels over a 24hour period suggested that these changes are likely to be due to bimodal diurnal variation which can alter serum MIC-1/GDF15 levels by about plus or minus 10% from the mesor. The lack of a rapid and substantial postprandial increase in MIC-1/GDF15 serum levels suggests that MIC1/GDF15 is unlikely to act as a satiety factor. Taken together, our findings suggest that MIC-1/GDF15 may be a physiological regulator of energy homeostasis in man, most probably due to actions on long-term regulation of energy homeostasis.
PLoS ONE 07/2015; 10(7):e0133362. DOI:10.1371/journal.pone.0133362 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insulin secretion is tightly controlled through coordinated actions of a number of systemic and local factors. Peptide YY (PYY) is expressed in alpha cells of the islet but its role in control of islet function such as insulin release is not clear. In this study, we generated a transgenic mouse model (Pyy(tg/+)/Rip-Cre) overexpressing the Pyy gene under the control of the rat insulin 2 (Ins2) gene promoter and assessed the impact of islet-released PYY on beta cell function, insulin release and glucose homeostasis in mice. Our results show that upregulation of PYY in islet beta-cells leads to an increase in serum insulin levels as well as improved glucose tolerance. Interestingly, PYY overproducing mice show increased lean mass and reduced fat mass with no significant changes in food intake or body weight. Energy expenditure is also increased accompanied by increased RER. Mechanistically, the enhanced in insulin levels and improved in glucose tolerance are primarily due to increased beta cell mass and secretion. This is associated with alterations in the expression of genes important for beta cell proliferation and function as well as the maintenance of the beta cell phenotype. Taken together, these data demonstrate that pancreatic islet-derived PYY plays an important role in controlling glucose homeostasis through the modulation of beta cell mass and function.
[Show abstract][Hide abstract] ABSTRACT: Emotions control evolutionarily conserved behavior that is central to survival in a natural environment. Imbalance within emotional circuitries, however, may result in malfunction and manifestation of anxiety disorders. Thus, a better understanding of emotional processes and in particular the interaction of the networks involved is of considerable clinical relevance. Although neurobiological substrates of emotionally controlled circuitries are increasingly evident their mutual influences are not. To investigate interactions between hunger and fear, we performed Pavlovian fear conditioning in fasted wildtype mice and in mice with genetic modification of a feeding-related gene. Furthermore we analyzed in these mice the electrophysiological microcircuits underlying fear extinction. Short-term fasting before fear acquisition specifically impaired long-term fear memory, while fasting before fear extinction facilitated extinction learning. Furthermore, genetic deletion of the Y4 receptor reduced appetite and completely impaired fear extinction, a phenomenon that was rescued by fasting. A marked increase in feed-forward inhibition between the basolateral and central amygdala has been proposed as a synaptic correlate of fear extinction and involves activation of the medial intercalated cells. This form of plasticity was lost in Y4KO mice. Fasting before extinction learning, however, resulted in specific activation of the medial intercalated neurons and re-established the enhancement of feed-forward inhibition in this amygdala microcircuit of Y4KO mice. Hence, consolidation of fear and extinction memories is differentially regulated by hunger suggesting that fasting and modification of feeding-related genes could augment the effectiveness of exposure therapy and provide novel drug-targets for treatment of anxiety disorders.Neuropsychopharmacology accepted article preview online, 11 June 2015. doi:10.1038/npp.2015.163.
Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 06/2015; DOI:10.1038/npp.2015.163 · 7.05 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The skeleton has recently emerged as an additional player in the control of whole-body glucose metabolism; however, the mechanism behind this is not clear.
Here we employ mice lacking neuropeptide Y, Y1 receptors solely in cells of the early osteoblastic lineage (Y1f3.6Cre), to examine the role of osteoblastic Y1 signalling in glycaemic control.
Y1f3.6Cre mice not only have a high bone mass phenotype, but importantly also display altered glucose homeostasis; significantly decreased pancreas weight, islet number and pancreatic insulin content leading to elevated glucose levels and reduced glucose tolerance, but with no effect on insulin induced glucose clearance. The reduced glucose tolerance and elevated bone mass was corrected in Y1f3.6Cre mice by bone marrow transplant from wildtype animals, reinforcing the osteoblastic nature of this pathway. Importantly, when fed a high fat diet, Y1f3.6Cre mice, while equally gaining body weight and fat mass compared to controls, showed significantly improved glucose and insulin tolerance. Conditioned media from Y1f3.6Cre osteoblastic cultures was unable to stimulate insulin expression in MIN6 cells compared to conditioned media from wildtype osteoblast, indicating a direct signalling pathway. Importantly, osteocalcin a secreted osteoblastic factor previously identified as a modulator of insulin secretion was not altered in the Y1f3.6Cre model.
This study identifies the existence of other osteoblast-derived regulators of pancreas function and insulin secretion and illustrates a mechanism by which NPY signalling in bone tissue is capable of regulating pancreatic function and glucose homeostasis.
[Show abstract][Hide abstract] ABSTRACT: The use of the click reaction for the introduction of conjugate groups such as affinity or fluorescent labels to a peptide for the study of peptide biochemistry and pharmacology is widespread. However, the nature and location of substituted 1,2,3-triazoles in peptide sequences may markedly impact conformation or binding as compared to native sequences. We have examined the preparation and application of propargyloxyproline (Pop) residues as a precursor to such peptide conjugates. Pop residues are available in a range of regio- and stereoisomers from hydroxyproline precursors and readily prepared in Fmoc-protected form. They can be incorporated routinely in peptide synthesis and broadly retain the conformational properties of parent proline containing peptides. This is exemplified by the preparation of biotin- and fluorophore-labelled peptides derived from linear and cyclic peptides.
Australian Journal of Chemistry 01/2015; 'Just Accepted'. · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The cocaine- and amphetamine-regulated transcript (CART) has been the subject of significant interest for over a decade. Work to decipher the detailed mechanism of CART function has been hampered by the lack of specific pharmacological tools like antagonists and the absence of a specific CART receptor(s). However, extensive research has been devoted to elucidate the role of the CART peptide and it is now evident that CART is a key neurotransmitter and hormone involved in the regulation of diverse biological processes, including food intake, maintenance of body weight, reward and addiction, stress response, psychostimulant effects and endocrine functions (Rogge et al., 2008; Subhedar et al., 2014). In this review, we focus on knowledge gained on CART's role in controlling appetite and energy homeostasis, and also address certain species differences between rodents and humans.
Frontiers in Neuroscience 10/2014; 8:313. DOI:10.3389/fnins.2014.00313 · 3.66 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Neuropeptide Y (NPY) and noradrenaline are commonly co-expressed in sympathetic neurons. Both are key regulators of energy homeostasis and critical for stress-coping. However, little is known about the specific function of NPY in the catechoalminergic system in these regulations. Here we show that mice with NPY expression only in the noradrenergic and adrenergic cells of the catecholaminergic system (catNPY) exhibited exacerbated diet-induced obesity, lower body and brown adipose tissue temperatures compared to WT and NPY-/- mice under a HFD. Furthermore, chronic stress increased adiposity and serum corticosterone level in WT but not NPY-/- mice. Re-introducing NPY specifically to the catecholaninergic system in catNPY mice restored stress responsiveness associated with increased respiratory exchange ratio and decreased liver pACC to tACC ratio. These results demonstrate catecholaminergic NPY signalling is critical in mediating diet- and chronic stress-induced fat gain via effects on diet-induced thermogenesis and stress-induced increases in corticosterone levels and lipogenic capacity.