Involvement of M1 and M3 receptors in isolated pancreatic islets function during weight cycling in ovariectomized rats

A growing understanding of the role of muscarinic receptors in the molecular pathology and treatment of schizophrenia

Pre-clinical models, postmortem and neuroimaging studies all support a role for muscarinic receptors in the molecular pathology of schizophrenia. From these data it was proposed that activation of the muscarinic M1 and/or M4 receptor would reduce the severity of the symptoms of schizophrenia. This hypothesis is now supported by results from two clinical trials which indicate that activating central muscarinic M1 and M4 receptors can reduce the severity of positive, negative and cognitive symptoms of the disorder. This review will provide an update on a growing body of evidence that argues the muscarinic M1 and M4 receptors have critical roles in CNS functions that are dysregulated by the pathophysiology of schizophrenia. This realization has been made possible, in part, by the growing ability to visualize and quantify muscarinic M1 and M4 receptors in the human CNS using molecular neuroimaging. We will discuss how these advances have provided evidence to support the notion that there is a sub-group of patients within the syndrome of schizophrenia that have a unique molecular pathology driven by a marked loss of muscarinic M1 receptors. This review is timely, as drugs targeting muscarinic receptors approach clinical use for the treatment of schizophrenia and here we outline the background biology that supported development of such drugs to treat the disorder.

Physiological profile regulation during weight gain and loss by ovariectomized females: importance of SIRT1 and SIRT4

Obesity in menopausal women occurs because of the systemic effects of loss of ovarian function, resulting in increased body weight and oxidative stress. Caloric restriction (CR) is essential for weight loss, since it provides benefits associated with metabolic normalization resulting from the action of sirtuins. The aim of this work was to evaluate the physiological effects of weight cycling in ovariectomized females. Females aged 2 mo (n = 8/group) were submitted to simulated surgery, ovariectomy (OVX group), and ovariectomy with weight fluctuation (WF group). In the WF group, weight cycling was performed two times, using 21 days of ad libitum commercial feed and 21 days of caloric restriction with 40% of the feed consumed by the OVX group. After 17 wk, the animals were evaluated experimentally. Weight fluctuations reduced triacylglycerol and the adipose tissue index of the WF animals, while increasing the expression of antioxidant proteins. In addition to causing fluctuations in the physiological parameters, the weight cycling led to increases of adipocyte number and serum fatty acids. These effects were reflected in increased expression of the sirtuin (SIRT) 1 and SIRT4 proteins, as well as protein complexes of the mitochondrial electron transport chain, especially in the liver and adipose tissues. The weight-cycling results suggested that mitochondrial and nuclear sirtuins were active in cellular signaling for the control of lipid metabolism, oxidative phosphorylation, and redox status. Weight cycling was able to restore the health characteristics of lean animals.

Caloric restriction recovers impaired β-cell-β-cell gap junction coupling, calcium oscillation coordination, and insulin secretion in prediabetic mice

Caloric restriction can decrease the incidence of metabolic diseases, such as obesity and Type 2 diabetes mellitus. The mechanisms underlying the benefits of caloric restriction involved in insulin secretion and glucose homeostasis are not fully understood. Intercellular communication within the islets of Langerhans, mediated by Connexin36 (Cx36) gap junctions, regulates insulin secretion dynamics and glucose homeostasis. The goal of this study was to determine whether caloric restriction can protect against decreases in Cx36 gap junction coupling and altered islet function induced in models of obesity and prediabetes. C57BL6 mice were fed with a high-fat diet (HFD), showing indications of prediabetes after 2 mo, including weight gain, insulin resistance, and elevated fasting glucose and insulin levels. Subsequently, mice were submitted to 1 mo of 40% caloric restriction (2 g/day of HFD). Mice under 40% caloric restriction showed reversal in weight gain and recovered insulin sensitivity, fasting glucose, and insulin levels. In islets of mice fed the HFD, caloric restriction protected against obesity-induced decreases in gap junction coupling and preserved glucose-stimulated calcium signaling, including Ca2+ oscillation coordination and oscillation amplitude. Caloric restriction also promoted a slight increase in glucose metabolism, as measured by increased NAD(P)H autofluorescence, as well as recovering glucose-stimulated insulin secretion. We conclude that declines in Cx36 gap junction coupling that occur in obesity can be completely recovered by caloric restriction and obesity reversal, improving Ca2+ dynamics and insulin secretion regulation. This suggests a critical role for caloric restriction in the context of obesity to prevent islet dysfunction.