neuropeptide-y and 2-mercaptoacetate

Neuropeptide Y (NPY) conjugated to saporin (NPY-SAP), a ribosomal inactivating toxin, is a newly developed compound designed to selectively target and lesion NPY receptor-expressing cells. We injected NPY-SAP into the basomedial hypothalamus (BMH), just dorsal to the arcuate nucleus (ARC), to investigate its neurotoxicity and to determine whether ARC NPY neurons are required for glucoprivic feeding. We found that NPY-SAP profoundly reduced NPY Y1 receptor and alpha MSH immunoreactivity, as well as NPY, Agouti gene-related protein (AGRP), and cocaine and amphetamine-related transcript mRNA expression in the BMH. NPY-SAP lesions were localized to the injection site with no evidence of retrograde transport by hindbrain NPY neurons with BMH terminals. These lesions impaired responses to intracerebroventricular (icv) leptin (5 microg/5 microl x d) and ghrelin (2 microg/5 microl), which are thought to alter feeding primarily by actions on ARC NPY/AGRP and proopiomelanocortin/cocaine and amphetamine-related transcript neurons. However, the hypothesis that NPY/AGRP neurons are required downstream mediators of glucoprivic feeding was not supported. Although NPY/AGRP neurons were destroyed by NPY-SAP, the lesion did not impair either the feeding or the hyperglycemic response to 2-deoxy-D-glucose-induced blockade of glycolysis use. Similarly, responses to glucagon-like peptide-1 (GLP-1, 5 microg/3 microl icv), NPY (5 microg/3 microl icv), cholecystokinin octapeptide (4 microg/kg ip), and beta-mercaptoacetate (68 mg/kg ip) were not altered by the NPY-SAP lesion. Thus, NPY-SAP destroyed NPY receptor-expressing neurons in the ARC and selectively disrupted controls of feeding dependent on those neurons but did not disrupt peptidergic or metabolic controls dependent upon circuitry outside the BMH.

Topics: Agouti-Related Protein; alpha-MSH; Amphetamines; Animals; Arcuate Nucleus of Hypothalamus; Binding, Competitive; Body Weight; Catecholamines; Cholecystokinin; Cocaine; Dopamine Uptake Inhibitors; Ghrelin; Glucagon; Glucagon-Like Peptide 1; Hypothalamus; Immunohistochemistry; In Situ Hybridization; Inhibitory Concentration 50; Intercellular Signaling Peptides and Proteins; Leptin; Ligands; Male; Models, Biological; Neurons; Neuropeptide Y; Peptide Fragments; Peptide Hormones; Peptides; Plant Proteins; Pro-Opiomelanocortin; Protein Binding; Protein Precursors; Proteins; Rats; Rats, Sprague-Dawley; Rhombencephalon; RNA, Messenger; Thioglycolates; Time Factors; Toxins, Biological

Using in situ hybridization, the mRNA levels encoding neuropeptide Y (NPY), agouti gene-related protein (AGRP), proopiomelanocortin (POMC), melanin-concentrating hormone (MCH) and hypocretin/orexin (HC/ORX) were investigated in the rat arcuate nucleus (Arc) and lateral hypothalamic area (LHA) 2 h after a single dose of the glucose antimetabolite 2-deoxy-D-glucose (2-DG; 600 mg/kg) or of the fatty acid oxidation inhibitor mercaptoacetate (MA; 600 mumol/kg). Two hours after 2-DG or MA injection food intake was significantly increased. NPY and AGRP mRNA levels in the Arc were increased by 2-DG but not affected by MA, and MCH mRNA levels in the LHA were increased by both antimetabolites. These results suggest that Arc neurons expressing NPY and AGRP are regulated by changes in glucose, but not fatty acid availability, whereas both factors affect MCH neurons in the LHA.

Topics: Agouti-Related Protein; Animals; Arcuate Nucleus of Hypothalamus; Carrier Proteins; Deoxyglucose; Eating; Hypothalamic Hormones; Hypothalamus; In Situ Hybridization; Intercellular Signaling Peptides and Proteins; Intracellular Signaling Peptides and Proteins; Male; Melanins; Neuropeptide Y; Neuropeptides; Neurotransmitter Agents; Orexins; Pituitary Hormones; Pro-Opiomelanocortin; Protein Biosynthesis; Proteins; Rats; Rats, Sprague-Dawley; RNA, Messenger; Thioglycolates

The effects of single injections of 2-deoxyglucose or 2-mercaptoacetate on the expression of mRNA of neuropeptide Y, pro-opiomelanocortin, and melanin-concentrating hormone in rat hypothalamus were studied by in situ hybridization in order to elucidate the role of these neuropeptides in the mechanisms of alimentary behavior caused by decreased levels of available fatty acids and glucose. The levels of neuropeptide Y mRNA in arcuate nuclei neurons are significantly increased under conditions of glucose deficiency, while the synthesis of melanin-concentrating hormone in the lateral hypothalamic neurons is increased in fatty acid deficiency. These data indicate that glyco- and lipodeprivation are different metabolic signals activating various neuropeptide systems responsible for alimentary behavior.

Topics: Animals; Carbohydrate Metabolism; Deoxyglucose; Fatty Acids; Gene Expression; Glucose; Hypothalamic Hormones; Hypothalamus; Lipid Metabolism; Male; Melanins; Neuropeptide Y; Neuropeptides; Pituitary Hormones; Pro-Opiomelanocortin; Rats; Rats, Sprague-Dawley; RNA, Messenger; Thioglycolates

This study examined the response of hypothalamic neuropeptide Y (NPY) to specific metabolic challenges. After intraperitoneal administration of 2-deoxy-D-glucose, which blocks glucose utilization, NPY levels measured via radioimmunoassay were significantly potentiated in the arcuate (ARC) and suprachiasmatic nuclei of the rat hypothalamus. The antimetabolite mercaptoacetate, in contrast, which blocks fatty acid oxidation, produced no significant change and actually tended to reduce NPY levels in the ARC. It is concluded that glucose utilization, in particular, may constitute an important signal, either direct or indirect, in the modulation of NPY production in the hypothalamus.

Topics: Animals; Arcuate Nucleus of Hypothalamus; Deoxyglucose; Glucose; Male; Neuropeptide Y; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Thioglycolates