Fasting and 17β-Estradiol Differentially Modulate the M-Current in Neuropeptide Y Neurons

Abstract

Multiple K+ conductances are targets for many peripheral and central signals involved in the control of energy homeostasis. Potential K+ channel targets are the KCNQ subunits that form the channels underlying the M-current, a sub-threshold, non-inactivating K+ current that is a common target for G-protein coupled receptors. Whole-cell recordings were made from GFP (Renilla)-tagged NPY neurons from the arcuate nucleus of the hypothalamus using protocols to isolate and characterize the M-current in these orexigenic neurons. We recorded robust K+ currents in the voltage range of the M-current, which were inhibited by the selective KCNQ channel blocker XE991 (40 µM), in both intact males and ovariectomized, 17β-estradiol (E2)-treated females. Since NPY neurons are orexigenic and are active during fasting, the M-current was measured in fed and fasted male mice. Fasting attenuated the XE991-sensitive current by 3-fold which correlated with decreased expression of the KCNQ2 and KCNQ3 subunits as measured with quantitative real-time PCR. Furthermore, E2 treatment augmented the XE991-sensitive M-current by 3-fold in ovariectomized (vs. oil-treated) female mice. E2-treatment increased the expression of the KCNQ5 subunit in females but not KCNQ2 or KCNQ3 subunits. Fasting in females abrogated the effects of E2 on M-current activity, at least in part, by decreasing KCNQ2 and KCNQ3 expression. In summary, these data suggest that the M-current plays a pivotal role in the modulation of NPY neuronal excitability and may be an important cellular target for neurotransmitter and hormonal signals in the control of energy homeostasis in both males and females.

Peptide hormone ghrelin enhances neuronal excitability by inhibition of Kv7/KCNQ channels

“…Most interestingly, ghrelin is able to modulate native Kv7/KCNQ channels expressed in nigral dopaminergic neurons, small DRG neurons and CA1 pyramidal neurons. In addition to the indicated three different types of neurons, ghrelin receptor and Kv7/KCNQ channels are also individually expressed in pituitary, neuropeptide Y neurons in hypothalamus and cortex 21,[40][41][42] , all of these suggest that the ghrelin signalling and Kv7/KCNQ suppression are likely common pathways primarily utilized by the central nervous system. Neuronal excitability is closely linked to dopamine release in the brain 43 and increased firing of dopamine neurons accelerates the dopamine release in the striatum, nucleus accumbens and cerebral cortex 43,44 .…”

“…Both Kv7/KCNQ channels and GHS-R are expressed in the SNc, hippocampus, dorsal root ganglion (DRG), hypothalamus and cortex 11,15,[17][18][19][20][21][22][23] . KCNQ channels are also negatively modulated by G-protein-coupled receptors via Gq and/ or G 11 activated phospholipase C (PLC)-mediated signal pathway [24][25][26] .…”

The membrane estrogen receptor ligand STX rapidly enhances GABAergic signaling in NPY/AgRP neurons: role in mediating the anorexigenic effects of 17β-estradiol

“…The NPY, GABA B-R1, and GABAB-R2 primer sequences were as previously published (36,58). Mouse PI3K p110␤ primers (218 bp product; acc.…”

“…These data collectively suggest that E 2 suppresses or augments GABA B -mediated currents in these orexigenic neurons through binding ER␣ or a putative Gq-mER, respectively. We previously have shown that NPY/AgRP neurons express ER␣ transcript and protein (36), and the cloning of the Gq-mER is a work in progress. Since the NPY/AgRP neurons that differentially responded to E 2 showed no physiological (i.e., resting membrane potential or input resistance) or anatomic (Fig.…”

“…In addition, E 2 reduces secretion of the peptide from immortalized hypothalamic neurons (11). We have shown that E 2 decreases the membrane excitability of NPY/AgRP neurons, at least partially, through increasing the expression of KCNQ5 channels, which augments the M-current (36). However, whether this anorectic steroid also modulates synaptic GABA B currents, as in POMC cells, remains unknown.…”