Inhibition by glucose or leptin of hypothalamic neurons expressing neuropeptide Y requires changes in AMP-activated protein kinase activity.
OBJECTIVE
Changes in the activity of glucose-excited and glucose-inhibited neurons within the basomedial hypothalamus are key to the central regulation of satiety. However, the molecular mechanisms through which these cells respond to extracellular stimuli remain poorly understood. Here, we investigate the role of 5'-AMP-activated protein kinase (AMPK), a trimeric complex encoded by seven distinct genes of the PRKA family, in the responses to glucose and leptin of each cell type.


METHODS
The activity of isolated rat basomedial hypothalamic neurons was assessed by: (1) recording cellular voltage responses under current clamp; (2) measuring intracellular free Ca(2+) with fluo-3 or fura-2; and (3) developing a neuropeptide Y (NPY) promoter-driven adenovirally produced ratiometric 'pericam' (a green fluorescent protein-based Ca(2+) sensor) to monitor [Ca(2+)] changes selectively in NPY-positive neurons.


RESULTS
The stimulatory effects of decreased (0 or 1.0 vs 15 mmol/l) glucose on glucose-inhibited neurons were mimicked by the AMPK activator, 5-amino-imidazole-4-carboxamide riboside (AICAR) and blocked by the inhibitor Compound C. Similarly, AICAR reversed the inhibitory effects of leptin in the majority of glucose-inhibited neurons. The responses to glucose of Npy-expressing cells, which represented approximately 40 % of all glucose-inhibited neurons, were also sensitive to Compound C or AICAR. Forced changes in AMPK activity had no effect on glucose-excited and non-glucose-responsive neurons.


CONCLUSIONS
Changes in AMPK activity are involved in the responses of glucose-inhibited neurons to large fluctuations in glucose concentration, and possibly also to leptin. This mechanism may contribute to the acute reduction of electrical activity and Ca(2+) oscillation frequency in these, but not other neurons, in the basomedial hypothalamus.
Mountjoy
P D
PD
Henry Wellcome Laboratories of Integrated Cell Signalling and Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol, UK.
Bailey
S J
SJ
Rutter
G A
GA
D055372:AMP-Activated Protein Kinases; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007031:Hypothalamus / Q000166:cytology* / Q000378:metabolism; D020738:Leptin / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009478:Neuropeptide Y / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011720:Pyrazoles / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012265:Ribonucleotides / Q000494:pharmacology
D007004:Hypoglycemic Agents; D020738:Leptin; D009097:Multienzyme Complexes; D009478:Neuropeptide Y; D011720:Pyrazoles; D011743:Pyrimidines; D012265:Ribonucleotides; C516138:dorsomorphin; D000620:Aminoimidazole Carboxamide; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide; D005947:Glucose; D002118:Calcium