Physiological and Molecular Characteristics of Rat Hypothalamic Ventromedial Nucleus Glucosensing Neurons

Abstract

To evaluate potential mechanisms for neuronal glucosensing, fura-2 Ca 2؉ imaging and single-cell RT-PCR were carried out in dissociated ventromedial hypothalamic nucleus (VMN) neurons. Glucose-excited (GE) neurons increased and glucose-inhibited (GI) neurons decreased intracellular Ca 2؉ ([Ca 2؉ ] i ) oscillations as glucose increased from 0.5 to 2.5 mmol/l. The Kir6.2 subunit mRNA of the ATP-sensitive K ؉ channel was expressed in 42% of GE and GI neurons, but only 15% of nonglucosensing (NG) neurons. Glucokinase (GK), the putative glucosensing gatekeeper, was expressed in 64% of GE, 43% of GI, but only 8% of NG neurons and the GK inhibitor alloxan altered [Ca 2؉ ] i oscillations in ϳ75% of GK-expressing GE and GI neurons. Insulin receptor and GLUT4 mRNAs were coexpressed in 75% of GE, 60% of GI, and 40% of NG neurons, although there were no statistically significant intergroup differences. Hexokinase-I, GLUT3, and lactate dehydrogenase-A and -B were ubiquitous, whereas GLUT2, monocarboxylate transporters-1 and -2, and leptin receptor and GAD mRNAs were expressed less frequently and without apparent relationship to glucosensing capacity. Thus, although GK may mediate glucosensing in up to 60% of VMN neurons, other regulatory mechanisms are likely to control glucosensing in the remaining ones. Diabetes 53:549 -559, 2004

Glucose sensing and the pathogenesis of obesity and type 2 diabetes

“…Attempts at localizing Glut2 in the brain has failed to show its expression in POMC or NPY neurons, although it was found to be associated with other hypothalamic and brainstem structures 63,[82][83][84][85] and expressed by neurons, astrocytes, endothelial cells and tanycytes of the third ventricle. [86][87][88] Thus, the regulation of orexigenic and anorexigenic peptide expressions by Glut2-dependent sensors may be controlled indirectly, possibly even by sensors located in other brain regions, such as the brainstem, in possible agreement with the reported presence in this structure of glucose-sensitive neurons that control feeding.…”

Agouti-Related Peptide and MC3/4 Receptor Agonists Both Inhibit Excitatory Hypothalamic Ventromedial Nucleus Neurons

“…Expression of GFP in vGluT2-expressing cells was verified with single-cell PCR. Harvesting of cytoplasmic RNA, reverse transcription (RT), and PCR were performed by modification of the previously described methods (Liss et al, 1999;Kang et al, 2004;Hirrlinger et al, 2005). Briefly, patch pipettes were back-loaded with 5 l of diethylpyrocarbonate-treated water and were used to harvest the cell cytoplasm.…”

Brain-derived neurotrophic factor in the ventromedial nucleus of the hypothalamus reduces energy intake

“…Early studies indicated that VMH lesions resulted in hyperphagia and obesity (28,38,66), whereas electrical stimulation of the VMH immediately suppressed feeding and induced lipolysis (65). Glucose-sensing neurons (7,27,55,74,75) and receptors for neuropeptides important to energy metabolism have been identified in the VMH, including leptin (13,17,20,22,51), melanocortin (26), neuropeptide Y (NPY) (43), corticotrophin-releasing hormone (49), CCK (12), insulin (33), and orexin (44) receptors. Many biological agents given into the VMH have been demonstrated to affect feeding.…”