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Christoph Melcher, Ruediger Bader and Michael J Pankratz

Feeding can be regulated by a variety of external sensory stimuli such as olfaction and gustation, as well as by systemic internal signals of feeding status and metabolic needs. Faced with a major health epidemic in eating-related conditions, such as obesity and diabetes, there is an ever increasing need to dissect and understand the complex regulatory network underlying the multiple aspects of feeding behavior. In this minireview, we highlight the use of Drosophila in studying the neural circuits that control the feeding behavior in response to external and internal signals. In particular, we outline the work on the neuroanatomical and functional characterization of the newly identified hugin neuronal circuit. We focus on the pivotal role of the central nervous system in integrating external and internal feeding-relevant information, thus enabling the organism to make one of the most basic decisions – to eat or not to eat.

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Helge Müller, Juliane Kröger, Olaf Jöhren, Silke Szymczak, Michael Bader, Peter Dominiak and Walter Raasch

AT1 blockers attenuate hypothalamo-pituitary–adrenal (HPA) axis reactivity in hypertension independently of their potency to lower blood pressure. A reduced pituitary sensitivity to CRH and a downregulation of hypothalamic CRH expression have been suggested to influence HPA axis activity during chronic AT1 blockade. This study was aimed at confirming the role of central angiotensin II in regulating HPA reactivity by using the transgenic rat TGR(ASrAOGEN), a model featuring low levels of brain angiotensinogen. Different stress tests were performed to determine HPA reactivity in TGR(ASrAOGEN) and appropriate controls. In TGR(ASrAOGEN), blood pressure was diminished compared to controls. The corticosterone response to a CRH or ACTH challenge and a forced swim test was more distinct in TGR(ASrAOGEN) than it was in controls and occurred independently of a concurrent enhancement in ACTH. Using quantitative real-time PCR, we found increased mRNA levels of melanocortin 2 (Mc2r) and AT2 receptors (Agtr2) in the adrenals of TGR(ASrAOGEN), whereas mRNA levels of Crh, Pomc, and AT1 receptors (Agtr1) remained unchanged in hypothalami and pituitary glands. Since stress responses were increased rather than attenuated in TGR(ASrAOGEN), we conclude that the reduced HPA reactivity during AT1 blockade could not be mimicked in a specific transgenic rat model featuring a centrally inactivated renin–angiotensin–aldosterone system. The ACTH independency of the enhanced corticosterone release during CRH test and the enhanced corticosterone response to ACTH rather indicates an adrenal mechanism. The upregulation of adrenal MC2 and AT2 receptors seems to be involved in the stimulated facilitation of adrenal corticosterone release for effectuating the stimulated stress responses.

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Robson A S Santos, Anderson J Ferreira, Thiago Verano-Braga and Michael Bader

Angiotensin (Ang)-(1–7) is now recognized as a biologically active component of the renin–angiotensin system (RAS). Ang-(1–7) appears to play a central role in the RAS because it exerts a vast array of actions, many of them opposite to those attributed to the main effector peptide of the RAS, Ang II. The discovery of the Ang-converting enzyme (ACE) homolog ACE2 brought to light an important metabolic pathway responsible for Ang-(1–7) synthesis. This enzyme can form Ang-(1–7) from Ang II or less efficiently through hydrolysis of Ang I to Ang-(1–9) with subsequent Ang-(1–7) formation by ACE. In addition, it is now well established that the G protein-coupled receptor Mas is a functional binding site for Ang-(1–7). Thus, the axis formed by ACE2/Ang-(1–7)/Mas appears to represent an endogenous counterregulatory pathway within the RAS, the actions of which are in opposition to the vasoconstrictor/proliferative arm of the RAS consisting of ACE, Ang II, and AT1 receptor. In this brief review, we will discuss recent findings related to the biological role of the ACE2/Ang-(1–7)/Mas arm in the cardiovascular and renal systems, as well as in metabolism. In addition, we will highlight the potential interactions of Ang-(1–7) and Mas with AT1 and AT2 receptors.