Roles for hypothalamic reactive oxygen species (ROS) in the modulation of circuit activity of the melanocortin system were proposed1,2,. Here we show that suppression of ROS diminished pro-opiomelanocortin (POMC) cell activation and promoted the activity of neuropeptide Y- (NPY)/agouti related peptide- (AgRP) neurons and feeding, whereas ROS activated POMC neurons and reduced feeding. ROS in POMC neurons were positively correlated with leptin levels in lean and ob/ob animals a relationship diminished in diet-induced obese (DIO) mice. High fat feeding resulted hypothalamic proliferation of peroxisomes and elevated PPARγ mRNA levels. Peroxisome proliferation in POMC neurons by the PPARγ agonist, rosiglitazone, decreased ROS levels and increased food intake in lean mice on high fat diet. Suppression of peroxisome proliferation in the hypothalamus by the PPAR antagonist, GW9662, increased ROS and c-fos expression in POMC neurons, reversed high fat feeding-triggered elevated NPY/AgRP and low POMC neuronal firing, and, resulted in decreased feeding of DIO mice. Finally, central administration of ROS alone increased c-fos and pStat3 expression in POMC neurons and reduced feeding of DIO animals. These observations unmask a previously unknown hypothalamic cellular event associated with peroxisomes and ROS in the central regulation of energy metabolism in states of leptin resistance.

We have shown that synaptic re-organization of hypothalamic feeding circuits in response to metabolic shifts involves astrocytes, cells that can directly respond to the metabolic hormone, leptin, in vitro. It is not known whether the role of glia cells in hypothalamic synaptic adaptions is active or passive. Here we show that leptin receptors are expressed in hypothalamic astrocytes and that conditional, adult deletion of leptin receptors in astrocytes leads to altered glial morphology, decreased glial coverage and elevated synaptic inputs onto pro-opiomelanocortin (POMC)- and Agouti-related protein (AgRP)-producing neurons. Leptin-induced suppression of feeding was diminished, while rebound feeding after fasting or ghrelin administration was elevated in mice with astrocyte-specific leptin receptor deficiency. These data unmask an active role of glial cells in the initiation of hypothalamic synaptic plasticity and neuroendocrine control of feeding by leptin.

Estradiol impacts a wide variety of brain processes, including sex differentiation, mood, and learning. Here we show that estradiol regulates auditory processing of acoustic signals in the vertebrate brain, more specifically in the caudomedial nidopallium (NCM), the songbird analog of the mammalian auditory association cortex. Multielectrode recordings coupled with local pharmacological manipulations in awake animals reveal that both exogenous and locally generated estradiol increase auditory-evoked activity in NCM. This enhancement in neuronal responses is mediated by suppression of local inhibitory transmission. Surprisingly, we also found that estradiol is both necessary and sufficient for the induction of multiple mitogen-activated protein kinase (MAPK)-dependent genes thought to be required for synaptic plasticity and memorization of birdsong. Specifically, we show that local blockade of estrogen receptors or aromatase activity in awake birds decrease song-induced MAPK-dependent gene expression. Infusions of estradiol in acoustically isolated birds induce transcriptional activation of these genes to levels comparable with song-stimulated animals. Our results reveal acute and rapid nongenomic functions for estradiol in central auditory physiology and suggest that such roles may be ubiquitously expressed across sensory systems.

Birdsong is a learned vocal behaviour that requires intact hearing for its development in juveniles and for its maintenance during adulthood. However, the functional organization of the brain circuits involved in the perceptual processing of song has remained obscure. Here we provide evidence that GABAergic mechanisms are an important component of these circuits and participate in the auditory processing of birdsong. We first cloned a zebra finch homologue of the gene encoding the 65-kDa isoform of glutamic acid decarboxylase (zGAD-65), a specific GABAergic marker, and conducted an expression analysis by in situ hybridization to identify GABAergic cells and to map their distribution throughout auditory telencephalic areas. The results showed that field L2, the caudomedial nidopallium (NCM) and the caudomedial mesopallium (CMM) contain a high number of GABAergic cells. Using patch-clamp brain slice recordings, we found abundant GABAergic mIPSCs in NCM. Pharmacological antagonism of mIPSCs induced large EPSC bursts, suggesting that tonic inhibition helps to stabilize NCM against runaway excitation via activation of GABA-A receptors. Next, using double fluorescence in situ hybridization and double immunocytochemical labelling, we demonstrated that large numbers of GABAergic cells in NCM and CMM show inducible expression of the transcriptional regulator ZENK in response to song auditory stimulation. These data provide direct evidence that GABAergic neurons in auditory brain regions are activated by song stimulation. Altogether, our results suggest that GABAergic mechanisms participate in auditory processing and perception, and might contribute to the memorization of birdsong.

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.

Formation of the sexually dimorphic nucleus of the pre‐optic area (SDN‐POA) in the rat hypothalamus shows a sexually differential development of neurons. Volume of the SDN‐POA in males is much bigger than that in females which is because of a neuroprotective effect of estradiol converted from circulating testosterone during a critical period of brain development. We found that neural epidermal growth factor‐like like‐2 (NELL2), a neural tissue‐enriched protein, is a potential downstream target of estrogen. In this study, we examined a possible role of NELL2 in the development of the SDN‐POA and in the normalcy of sexual behavior in the male rats. NELL2 was expressed and co‐localized with estrogen receptor alpha in the SDN‐POA. A blockade of NELL2 synthesis in the brain during postnatal day 0 (d0) to d4 by an intracerebroventricular injection of an antisense NELL2 oligodeoxynucleotide, resulted in a decrease in volume of the SDN‐POA in males. Interestingly, it reduced some components of the male sexual behavior such as mounting and intromission, but not the sexual partner preference in adulthood. In vitro study using the hippocampal neuroprecursor HiB5 cells showed that NELL2 has a protective effect from a cell death condition. These data suggest that a relevant expression of NELL2 in the neonatal brain is important for the estrogen‐induced normal development of the SDN‐POA and the normalcy of sexual behavior in male rats.

Fig. 1. Bone cells express Avprs. Immunofluorescence micrographs (A) and Western immunoblotting (B)show the expression of Avpr1α in osteoblasts and osteoclasts, and as a function of osteoblast (mineralization) and osteoclast (with Rankl) differentiation. The expression of Avp (ligand) and Avpr1α (receptor) in osteoblasts is regulated by 17β-estradiol, as determined by quantitative PCR (C) and Western immunoblotting (D). (Magnification: A, 63×.) Because Avp is a small peptide, its precursor neurophysin II is measured. Statistics: Student t test, P values shown compared with 0 h. Stimulation of Erk phosphorylation (p-Erk) as a function of total Erk (t-Erk) by Avp (10 −8 M) in osteoclast precursors (preosteoclasts), osteoclasts (OC), and osteoblasts establishes functionality of the Avpr1α in the presence or absence of the receptor inhibitor SR49059 (10 −8 M) (E). Western immunoblotting showing the expression of Avpr2 in preosteoclasts, OCs (F), and osteoblasts (G) isolated from Avpr1α −/− mice, as well as in MC3T3.E1 osteoblast precursors (G). Functionality of Avpr2 was confirmed by the demonstration that cells from Avpr1α −/− mice remained responsive to AVP in reducing the expression of osteoblast differentiation genes, namely Runx2, Osx, Bsp, Atf4, Opn, and Osteocalcin (quantitative PCR, P values shown) (H). Only relevant bands from Western blots are shown, with gaps introduced where empty lanes are excised to conserve space.

Obesity and metabolic disorders, such as type 2 diabetes and hypertension, have attracted considerable attention as life-threatening diseases not only in developed countries but also worldwide. Additionally, the rate of obesity in young people all over the world is rapidly increasing. Accumulated evidence suggests that the central nervous system may participate in the development of and/or protection from obesity. For example, in the brain, the hypothalamic melanocortin system senses and integrates central and peripheral metabolic signals and controls the degree of energy expenditure and feeding behavior, in concert with metabolic status, to regulate whole-body energy homeostasis. Currently, researchers are studying the mechanisms by which peripheral metabolic molecules control feeding behavior and energy balance through the central melanocortin system. Accordingly, recent studies have revealed that some inflammatory molecules and transcription factors participate in feeding behavior and energy balance by controlling the central melanocortin pathway, and have thus become new candidates as therapeutic targets to fight metabolic diseases such as obesity and diabetes.