Activation of central PPARγ promotes food intake and body weight gain; however, the identity of the neurons that express PPARγ and mediate the effect of this nuclear receptor on energy homeostasis is unknown. Here, we determined that selective ablation of PPARγ in murine proopiomelanocortin (POMC) neurons decreases peroxisome density, elevates reactive oxygen species, and induces leptin sensitivity in these neurons. Furthermore, ablation of PPARγ in POMC neurons preserved the interaction between mitochondria and the endoplasmic reticulum, which is dysregulated by HFD. Compared with control animals, mice lacking PPARγ in POMC neurons had increased energy expenditure and locomotor activity; reduced body weight, fat mass, and food intake; and improved glucose metabolism when exposed to high-fat diet (HFD). Finally, peripheral administration of either a PPARγ activator or inhibitor failed to affect food intake of mice with POMC-specific PPARγ ablation. Taken together, our data indicate that PPARγ mediates cellular, biological, and functional adaptations of POMC neurons to HFD, thereby regulating whole-body energy balance.

SummaryDeficits in learning and memory accompanied by agerelated neurodegenerative diseases are closely related to the impairment of synaptic plasticity. In this study, we investigated the role of thiol redox status in the modulation of the N-methyl-D-aspartate receptor (NMDAR)-dependent long-term potentiation (LTP) in CA1 areas of hippocampal slices. Our results demonstrated that the impaired LTP induced by aging could be reversed by acute administration of reductants that can regulate thiol redox status directly, such as dithiothreitol or b-mercaptoethanol, but not by classical anti-oxidants such as vitamin C or trolox. This repair was mediated by the recruitment of aging-related deficits in NMDAR function induced by these reductants and was mimicked by glutathione, which can restore the age-associated alterations in endogenous thiol redox status. Moreover, antioxidant prevented but failed to reverse H 2 O 2 -induced impairment of NMDARmediated synaptic plasticity. These results indicate that the restoring of thiol redox status may be a more effective strategy than the scavenging of oxidants in the treatment of pre-existing oxidative injury in learning and memory.

Dopamine, an important neurotransmitter in brain, exerts its action via dopamine receptors, which are known to belong to the G-protein-coupled receptor family. Calcium plays a critical role in mediating neuronal excitability and neuroplasticity. Regulation of calcium content in neuronal cells by dopamine has been reported in different experimental systems (Bergson et al. 2003;Lee et al. 2004;Neve et al. 2004). Both protein kinase A (PKA)-dependent and independent mechanisms have been proposed to mediate dopamine receptor-stimulated calcium signals (Tang et al. 2003;Neve et al. 2004). Recent evidence indicates that activation of dopamine receptors also activates phospholipase Cb (PLC b ) through coupling to the Gq protein, resulting in hydrolysis of phosphatidylinositol into diacylglycerol and inositol triphosphate (IP3;Felder et al. 1989;Frail et al. 1993;Pacheco and Jope 1997; Lezano & Bergson., 2001;Lee et al. 2004;Wirtshafter and Osborn, 2005;Panchalingam and Undie 2005;Zhang et al. 2005). This stimulation of phosphatidylinositol hydrolysis appears to be mediated by a D1-like receptor as only selective D1 receptor agonist but not D2 receptor agonist can elicit this action, which is blocked by SCH23390, a selective D1 receptor antagonist (Undie et al. 1994). However, the stimulation of phosphatidylinositol hydrolysis by the D 1 -like receptor appears to be distinct from the D 1A receptor because in D 1A transfected PC12 cells there is no detectable D1 receptor-stimulated IP3 generation (Jin et al. 2002), and in D 1A knock-out mice the stimulation of IP 3 by D1 agonist in brain was still present even though the effect can be blunted by a D1 antagonist (Friedman et al.

. PI3K integrates the effects of insulin and leptin on large-conductance Ca 2ϩ -activated K ϩ channels in neuropeptide Y neurons of the hypothalamic arcuate nucleus. Am J Physiol Endocrinol Metab 298: E193-E201, 2010. First published August 11, 2009; doi:10.1152/ajpendo.00155.2009.-The adipocyte-derived hormone leptin and the pancreatic ␤-cell-derived hormone insulin function as afferent signals to the hypothalamus in an endocrine feedback loop that regulates body adiposity. They act in hypothalamic centers to modulate the function of specific neuronal subtypes, such as neuropeptide Y (NPY) neurons, by modifying neuronal electrical activity. To investigate the intrinsic activity of these neurons and their responses to insulin and leptin, we used a combination of morphological features and immunocytochemical technique to identify the NPY neurons of hypothalamic arcuate nucleus (ARC) and record whole cell large-conductance Ca 2ϩ -activated potassium (BK) currents on them. We found that both of the hormones increase the peak amplitude of BK currents, shifting the steady-state activation curve to the left. The effect of both insulin and leptin can be prevented by pretreatment with inhibitors of tyrosine kinase and phosphatidylinositol 3-kinase (PI3K) but not MAPK. These data indicate that PI3K-mediated signals are the common regulators of BK channels by insulin and leptin and mediated the two hormones' identical activatory effects on ARC NPY neurons. The effect of insulin and leptin together was similar to that of insulin or leptin alone, and leptin or insulin pretreatment did not lead to insulin-or leptin-sensitizing effects, respectively. These intracellular signaling mechanisms may play key roles in regulating ARC NPY neuron activity and physiological processes such as the control of food intake and body weight, which are under the combined control of insulin and leptin. patch-clamp recording; phosphatidylinositol 3-kinase INSULIN AND LEPTIN ARE HYPOTHESIZED to be "adiposity signals" for the long-term regulation of energy balance in the brain (2,36,40,50). They circulate at levels that are directly proportional to adipose mass and enter the central nervous system (CNS) via saturable receptor-mediated processes (4, 18, 49). The primary CNS target for these adipostats is the arcuate nucleus (ARC), where leptin and insulin receptors are highly expressed (32, 45), and direct administration of either hormone has a potent effect on food intake and body weight (1,28,35). Two specific ARC neuron populations have been strongly implicated in sensing the changes in levels of circulating leptin and insulin and transducing these signals into neuronal outputs (2, 36). They are proopiomelanocortin (POMC)-containing neurons, which are associated with catabolism, and neuropeptide Y (NPY)/agouti gene-related protein (AgRP)-containing neurons, which are associated with anabolism. As adipostatic hormones, insulin and leptin have a similar transcriptional control on these regulatory entities in the hypothalamus. Both of them can inc...

Acid-sensing ion channels (ASICs) extensively exist in both central and peripheral neuronal systems and contribute to many physiological and pathological processes. The protein that interacts with C kinase 1 (PICK1) was cloned as one of the proteins interacting with protein kinase C (PKC) and colocalized with ASIC1 and ASIC2. Here, we used PICK1 knockout (PICK1-KO) C57/BL6 mice together with the whole cell patch clamp, calcium imaging, RT-PCR, Western blot, and immunocytochemistry techniques to explore the possible change in ASICs and the regulatory effects of PKC on ASICs. The results showed that PICK1 played a key role in regulation of ASIC functions. In PICK1-KO mouse cortical neurons, both the amplitude of ASIC currents and elevation of [Ca(2+)](i) mediated by acid were decreased, which were attributable to the decreased expression of ASIC1a and ASIC2a proteins in the plasma membrane. PKC, a partner protein of PICK1, regulated ASIC functions via PICK1. The agonist and antagonist of PKC only altered ASIC currents and acid-induced increase in [Ca(2+)](i) in wild-type, but not in KO mice. In conclusion, our data provided the direct evidence from PICK1-KO mice that a novel target protein, PICK1, would regulate ASIC function and membrane expression in the brain. In addition, PICK1 played the bridge role between PKC and ASICs.

Recent evidences indicate the existence of an atypical D(1) dopamine receptor other than traditional D(1) dopamine receptor in the brain that mediates PI hydrolysis via activation of phospholipase C(beta) (PLC(beta)). To further understand the basic physiological function of this receptor in brain, the effects of a selective phosphoinositide (PI)-linked D(1) dopamine receptor agonist SKF83959 on cytosolic free calcium concentration ([Ca(2+)](i)) in cultured rat prefrontal cortical astrocytes were investigated by calcium imaging. The results indicated that SKF83959 caused a transient dose-dependent increase in [Ca(2+)](i). Application of D(1) receptor, but not D(2), alpha(1) adrenergic, 5-HT receptor, or cholinergic antagonist prevented SKF83959-induced [Ca(2+)](i) rise, indicating that activation of the D(1) dopamine receptor was essential for this response. Increase in [Ca(2+)](i) was a two-step process characterized by an initial increase in [Ca(2+)](i) mediated by release from intracellular stores, supplemented by influx through voltage-gated calcium channels, receptor-operated calcium channels, and capacitative Ca(2+) entry. Furthermore, SKF83959-stimulated increase in [Ca(2+)](i) was abolished following treatment with a PLC inhibitor. Overall, these results suggested that activation of D(1) receptor by SKF83959 mediates a dose-dependent mobilization of [Ca(2+)](i) via the PLC signaling pathway in cultured rat prefrontal cortical astrocytes.

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Chronic stress induces altered energy metabolism and plays important roles in the etiology of depression, in which the glucocorticoid negative feedback is disrupted due to imbalanced glucocorticoid receptor (GR) functions. The mechanism underlying the dysregulation of GR by chronic stress remains elusive. In this study, we investigated the role of AMP-activated protein kinase (AMPK), the key enzyme regulating cellular energy metabolism, and related signaling pathways in chronic stress-induced GR dysregulation. In cultured rat cortical astrocytes, glucocorticoid treatment decreased the level, which was accompanied by the decreased expression of liver kinase B1 (LKB1) and reduced phosphorylation of AMPK. Glucocorticoid-induced effects were attenuated by glucocorticoid-inducible kinase 1 (SGK1) inhibitor GSK650394, which also inhibited glucocorticoid induced phosphorylation of Forkhead box O3a (FOXO3a). Furthermore, glucocorticoid-induced down-regulation of GR was mimicked by the inhibition of AMPK and abolished by the AMPK activators or the histone deacetylase 5 (HDAC5) inhibitors. In line with the role of AMPK in GR expression, AMPK activator metformin reversed glucocorticoid-induced reduction of AMPK phosphorylation and GR expression as well as behavioral alteration of rats. Taken together, these results suggest that chronic stress activates SGK1 and suppresses the expression of LKB1 via inhibitory phosphorylation of FOXO3a. Downregulated LKB1 contributes to reduced activation of AMPK, leading to the dephosphorylation of HDAC5 and the suppression of transcription of GR.