LVA Calcium channels regulate excitability of hypothalamic POMC+ Neurons and indirectly affect sensitivity to leptin

PERISSINOTTI PP; HE Y; ETHINGTON EG; KOOB MD; PIEDRAS-RENTERÍA ES

Washington, DC

Congreso; Society for Neuroscience; 2014

Low voltage-activated (LVA) T-type calcium channels play critical roles in neuronal excitability. Here we confirm the involvement of T-type channel activation in the excitability and generation of action potentials (APs) in cultured hypothalamic neurons. The specific T-type channel blocker NNC 55-0396 reduced neuronal excitability and prevented post-inhibitory rebound (PIR) responses. The Kelch-like 1 (KLHL1) KO mouse model displays homeostatic changes in the expression of LVA calcium channels, resulting in a down-regulation of the CaV3.2 alpha1H isoform in whole brain and cerebellum, in line with this protein's function as a positive modulator of CaV3.2. In the hypothalamus, however, alpha1H signal did not decrease significantly, and biophysical and western blot analysis show the CaV3.1 alpha1G isoform is up-regulated, with a 40 % increase in T-type current density in cultured hypothalamic KLHL1-KO neurons compared to WT. A leftward shift and slight increase in window currents was observed, but not a change in resting membrane. We found that the excitability and PIR probability of KLHL1-KO neurons was increased compared to WT, and that the spontaneously firing neurons displayed a decreased mean-intraburst interval. T-type channels are potential therapeutic targets for treatment of obesity, and interestingly, the KLHL1-KO mice were adult-onset overweight. Leptin treatment (100 nM) resulted in membrane depolarization and increased excitability in WT neurons; this effect was prevented by treatment with NNC 55-0396. In contrast, KLHL1-KO neurons exhibited a basal excitability similar to the leptin-treated WT group; and leptin treatment did not elicit further depolarization. Leptin action occurred via TRPC1 channels, as pre-treatment with 100 uM 2-APB decreased the number of APs by 20% and its application after leptin treatment produced a 50% reduction. Our data suggest that leptin activation of TRPC1 channels induces neuronal depolarization of the membrane that recruits T-type channel activity. Hypothalamic neuronal excitability in KLHL1-KO neurons is increased, rendering its neurons leptin-resistant. This mouse model provides insights into the modulation of the hypothalamic excitability by alpha1G and its impact in obesity disorders.