Deciphering intracellular localization and physiological role of nociceptin and nocistatin

Nociceptin and nocistatin are endogenous ligands of G protein coupled receptor family. Numerous techniques have been used to study the diverse parameters including, localization, distribution and ultrastructure of these peptides. The majority of the study parameters are based on their physiological roles in different organ systems. The present study presents an overview of the different methods used for the study of nociceptin, nocistatin and their receptors. Nociceptin has been implicated in many physiological functions including, nociception, locomotion, stressed-induced analgesia, learning and memory, neurotransmitter and hormone release, renal function, neuronal differentiation, sexual and reproductive behavior, uterine contraction, feeding, anxiety, gastrointestinal motility, cardiovascular function, micturition, cough, hypoxic-ischemic brain injury, diuresis and sodium balance, temperature regulation, vestibular function, and mucosal transport. It has been noted that the use of light and electron microscopy was less frequent, though it may be one of the most promising tools to study the intracellular localization of these neuropeptides. In addition, more studies on the level of circulating nociceptin and nocistatin are also necessary for investigating their clinical roles in health and disease. A variety of modern tools including physiological, light and electron microscopy (EM) are needed to decipher the extent of intracellular localization, tissue distribution and function of these peptides. The intracellular localization of nociceptin and nocistatin will require a high resolution transmission EM capable of identifying these peptides and other supporting molecules that co-localize with them. A tracing technique could also elucidate a possible migratory ability of nociceptin and nocistatin from one cellular compartment to the other. © 2013 Elsevier Inc

Distribution of Nociceptin in Pancreatic Islet Cells of Normal and Diabetic Rats

OBJECTIVES: Nociceptin has been reported to play an important role in the regulation of pancreatic exocrine secretion. Most of the studies performed on nociceptin are mainly physiological rather than morphological in nature. The present study investigated the pattern of distribution of nociceptin in the endocrine pancreas of normal and diabetic rats. METHODS: Immunohistochemistry, immunofluorescence, Western blot, and double-labeled immunoelectron microscopy were used in this study. Diabetes was induced using streptozotocin (60 mg/kg body weight). RESULTS: Nociceptin-immunoreactive cells were observed in the central and peripheral regions of the islets of both normal and diabetic rat pancreas. The number of nociceptin-positive cells was significantly (P < 0.05) lower in the islet of diabetic rats compared with the control. Immunofluorescence study showed that nociceptin colocalizes with insulin in pancreatic beta-cells. The degree of colocalization of nociceptin with insulin was severely deranged after the onset of diabetes. Moreover, immunogold particles conjugated with either nociceptin or insulin were observed on the granules of pancreatic beta-cell. The number of nociceptin-labeled colloidal gold particles was significantly lower after the onset of diabetes. CONCLUSIONS: Nociceptin is present in pancreatic islets cells and colocalizes with insulin. Nociceptin may have a physiological role in the metabolism of insulin