Electrical Inhibition of Identified Anorexigenic POMC Neurons by Orexin/Hypocretin

Abstract

Proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus (ARC) suppress appetite, and lack of POMC-derived peptides or electrical silencing of POMC neurons causes obesity. ARC POMC neurons are surrounded by nerve terminals containing the wakefulness-promoting peptides orexins/hypocretins, but whether orexin affects their electrical activity has not been tested directly. Here we identify living ARC POMC cells in mouse brain slices by targeted expression of green fluorescent protein. Using whole-cell patch-clamp recordings, we show that orexin suppresses the spontaneous action potential firing of these neurons. Orexin-induced inhibition involves membrane hyperpolarization, a decreased excitatory synaptic drive, and an increased frequency of GABAergic inputs. Our results suggest a reduction in the electrical activity of ARC POMC neurons, which is mediated by changes in presynaptic inputs, contributes to the appetite-enhancing action of orexins.

Acute Suppressive and Long-Term Phase Modulation Actions of Orexin on the Mammalian Circadian Clock

“…In other parts of the hypothalamus and brainstem, orexin excites local GABAergic interneurons to presynaptically regulate GABAergic transmission Liu et al, 2002;Eriksson et al, 2004;Ma et al, 2007). In our daytime SCN recordings, focal application of gabazine into the SCN blocked orexin's suppression of the Per1-EGFP neurons, thereby showing that orexin can increase the frequency of GABA-mediated IPSCs, presumably by increasing GABA release from local SCN neurons.…”

Glucagon-Like Peptide 1 Stimulates Hypothalamic Proopiomelanocortin Neurons

“…Fluorescent POMC-eGFP neurons were identified by epifluorescence and patched under IR-DIC optics. Whole-cell current-clamp and voltageclamp recordings were made using an EPC-9 patch-clamp amplifier, as described previously (Burdakov and Ashcroft, 2002;Plum et al, 2006;Ma et al, 2007). Patch pipettes had resistances of 3-5 M⍀ when filled with internal solution.…”

“…The peak inward current and current-voltage ( I-V) relationships were measured. Resting potentials of firing neurons were determined from slow time-scale recordings on which a clear basal line was evident; this baseline was taken as the resting potential (Plum et al, 2006;Ma et al, 2007). Fold increases in firing were determined individually for each neuron and then averaged.…”

Orexin/Hypocretin: A Neuropeptide at the Interface of Sleep, Energy Homeostasis, and Reward System

“…The Arc receives projections densely from orexin neurons Date et al, 1999;Yamanaka et al, 2000), and Fos expression was induced in NPY neurons of the arcuate nucleus by intracerebroventricular injection of orexin, suggesting that orexinstimulated feeding may occur at least partly through NPY pathways (Yamanaka et al, 2000). Electrophysiological data showed that orexin directly and indirectly activated NPY neurons (van den Top et al, 2004; Li and 170 van den Pol, 2006) but inhibited POMC neurons (Muroya et al, 2004;Ma et al, 2007). Furthermore, the orexin A-induced increase in food intake was partly inhibited by prior administration of BIBO3304, an NPY-Y1 receptor antagonist, in a dose-dependent manner (Yamanaka et al, 2000).…”