478.07/JJJ21. Mechanism of leptin action on arousal.

BECK PB; URBANO FJ; GARCIA-RILL E

San Diego, CA, USA.

Congreso; 2013 Society for Neuroscience Meeting.; 2013

Society for Neuroscience

Leptin, a hormone that regulates appetite and energy expenditure, is increased in obese individuals, although these individuals often exhibit leptin resistance. Obesity is characterized by sleep/wake disturbances, such as excessive daytime sleepiness in the absence of sleep-disordered breathing, increased REM sleep, increased nighttime arousals, increased total wake time, and decreased percentage of total sleep. Several studies have shown that short sleep duration is highly correlated with decreased leptin levels in both animal and human models. Arousal and REM sleep are regulated by the cholinergic arm of the reticular activating system, the pedunculopontine nucleus (PPN). The goal of this project is to determine the intracellular mechanism of leptin in the PPN, and thus the possible link between obesity and related sleep disorders. We previously found that leptin causes a partial blockade of Na+ channel conductance and h-current (IH) in PPN cells, leading to decreased activity in the PPN. We thus investigated the intracellular mechanisms by which leptin may act on PPN cells. Here, we show that the mechanism of leptin?s effect is G-protein-dependent and can be blocked by the super-active leptin antagonist (SLAN-4). Whole cell patch clamp recordings were conducted on 9-17 day old rat brainstem slices in the presence of the synaptic blockers gabazine (GABAA antagonist), strychnine (glycine antagonist), 6-cyano-7-nitroquinoxaline-2,3-dione (AMPA/kainate receptor antagonist), and APV (NMDA receptor antagonist) for Ih experiments; synaptic blockers plus tetraethylammonium chloride (to block K+channels), cadmium and nickel chloride (to block Ca2+ channels) were used in the Na+ current experiments. We found that SLAN-4 reduced the blockade of INa ~50%) and IH (~93%) caused by leptin. Intracellular GDPβ [(a G-protein inhibitor) significantly blocked the effect of leptin on INa (~60%) but not on IH (~25%). Intracellular GTPγS (a G-protein activator) blocked the effect of leptin on both INa (~80%) and IH (~90%). These results suggest that the effects of leptin on the intrinsic properties of PPN neurons are G-protein dependent and can be blocked by SLAN-4. We also found that leptin enhanced NMDA receptor-mediated responses in single neurons and in the PPN population as a whole, an effect blocked by SLAN-4. These results show that leptin?s effect on PPN cells is not only G-protein dependent, but also receptor mediated. We hypothesize that leptin normally decreases activity in the PPN by reducing IH and INa currents, and that in obesity, this effect may be blunted due to leptin resistance, leading to increased arousals and REM sleep drive. GRANTS: NIH award F30-HL108429 NRSA; NIH grant R01 NS020246; NIH grant P20 GM103425; ANPCyT-FONCyT-BID 1728 OC.AR. PICT 2008-2019.