ABSTRACT
Chronic morphine treatment and naloxone precipitated morphine withdrawal activates stress-related brain circuit and results in significant changes in food intake, body weight gain and energy metabolism. The present study aimed to reveal hypothalamic mechanisms underlying these effects. Adult male rats were made dependent on morphine by subcutaneous implantation of constant release drug pellets. Pair feeding revealed significantly smaller weight loss of morphine treated rats compared to placebo implanted animals whose food consumption was limited to that eaten by morphine implanted pairs. These results suggest reduced energy expenditure of morphine-treated animals. Chronic morphine exposure or pair feeding did not significantly affect hypothalamic expression of selected stress- and metabolic related neuropeptides - corticotropin-releasing hormone (CRH), urocortin 2 (UCN2) and proopiomelanocortin (POMC) compared to placebo implanted and pair fed animals. Naloxone precipitated morphine withdrawal resulted in a dramatic weight loss starting as early as 15-30 min after naloxone injection and increased adrenocorticotrophic hormone, prolactin and corticosterone plasma levels in morphine dependent rats. Using real-time quantitative PCR to monitor the time course of relative expression of neuropeptide mRNAs in the hypothalamus we found elevated CRH and UCN2 mRNA and dramatically reduced POMC expression. Neuropeptide Y (NPY) and arginine vasopressin (AVP) mRNA levels were transiently increased during opiate withdrawal. These data highlight that morphine withdrawal differentially affects expression of stress- and metabolic-related neuropeptides in the rat hypothalamus, while relative mRNA levels of these neuropeptides remain unchanged either in rats chronically treated with morphine or in their pair-fed controls.
Subject(s)
Gene Expression Regulation/drug effects , Hypothalamus/drug effects , Morphine Dependence/genetics , Morphine/pharmacology , Neuropeptides/metabolism , Stress, Physiological/drug effects , Stress, Physiological/genetics , Adrenocorticotropic Hormone/blood , Animals , Arginine Vasopressin/genetics , Arginine Vasopressin/metabolism , Behavior, Animal/drug effects , Corticotropin-Releasing Hormone/genetics , Corticotropin-Releasing Hormone/metabolism , Disease Models, Animal , Energy Metabolism/drug effects , Hypothalamus/metabolism , Male , Morphine/chemistry , Morphine Dependence/metabolism , Morphine Dependence/pathology , Neuropeptides/genetics , Pro-Opiomelanocortin/genetics , Pro-Opiomelanocortin/metabolism , Rats , Rats, Wistar , Urocortins/genetics , Urocortins/metabolismABSTRACT
Many signals reflecting energy balance and stress are integrated at the hypothalamic orexigenic NPY neurons. To determine transcriptional changes of the NPY gene in response to stress, we followed the time course and compared the expression of heteronuclear (hn)- and messenger (m)RNA levels by in situ hybridization histochemistry and by real time PCR in mice following insulin-induced hypoglycemia and restraint. Hypoglycemia in fasted mice resulted in a rapid increase of NPY hnRNA that peaked at 1h, declined thereafter by 2-4h after insulin injection and run parallel to that of NPY mRNA. Throughout the time course examined, NPY expressing cells in the medial basal hypothalamus remained overwhelmingly localized to the arcuate nucleus. Following restraint NPY mRNA slightly increased, however hnRNA levels decreased up to 2h, suggesting increased stability of mature NPY mRNA. These results highlight rapid changes and differential regulation of NPY expression in response to metabolic and stress challenges.
