Nitric oxide (NO) was described to inhibit the proliferation of neural stem cells. Some evidence suggests that NO, under certain conditions, can also promote cell proliferation, although the mechanisms responsible for a potential proliferative effect of NO in neural stem cells have remained unaddressed. In this work, we investigated and characterized the proliferative effect of NO in cell cultures obtained from the mouse subventricular zone. We found that the NO donor NOC-18 (10 lM) increased cell proliferation, whereas higher concentrations (100 lM) inhibited cell proliferation. Increased cell proliferation was detected rapidly following exposure to NO and was prevented by blocking the mitogen-activated kinase (MAPK) pathway, independently of the epidermal growth factor (EGF) receptor. Downstream of the EGF receptor, NO activated p21Ras and the MAPK pathway, resulting in a decrease in the nuclear presence of the cyclin-dependent kinase inhibitor 1, p27 KIP1 , allowing for cell cycle progression. Furthermore, in a mouse model that shows increased proliferation of neural stem cells in the hippocampus following seizure injury, we observed that the absence of inducible nitric oxide synthase (iNOS 2/2 mice) prevented the increase in cell proliferation observed following seizures in wild-type mice, showing that NO from iNOS origin is important for increased cell proliferation following a brain insult. Overall, we show that NO is able to stimulate the proliferation of neural stem cells bypassing the EGF receptor and promoting cell division. Moreover, under pathophysiological conditions in vivo, NO from iNOS origin also promotes proliferation in the hippocampus. STEM CELLS

The state of somatic energy stores in metazoans is communicated to the brain, which regulates key aspects of behaviour, growth, nutrient partitioning and development 1 . The central melanocortin system acts through Melanocortin-4 Receptor (MC4R) to control appetite, food intake and energy expenditure 2 . We now present evidence that the Melanocortin-3 Receptor (MC3R) regulates the timing of sexual maturation, the rate of linear growth and the accrual of lean mass, all energy-sensitive processes. We found that humans who carry loss-of-function mutations in MC3R, including a rare homozygote, have a later onset of puberty. Consistent with previous findings in mice, they also had reduced linear growth, lean mass and IGF-1 levels. Mice lacking Mc3r had delayed sexual maturation and an insensitivity of reproductive cycle length to nutritional perturbation. The expression of Mc3r is enriched in hypothalamic neurons controlling reproduction and growth and increases during post-natal development in a manner consistent with a role in regulation of sexual maturation. These findings suggest a bifurcating model of nutrient sensing by the central melanocortin pathway with signalling through MC4R controlling the acquisition and retention of calories, while MC3R primarily regulates their disposition into growth, lean mass and the timing of sexual maturation.

The contribution of neuropeptide Y (NPY), deriving from adrenal medulla, to the adrenosympathetic tone is unknown. We found that in response to NPY, primary cultures of mouse adrenal chromaffin cells secreted catecholamine, and that this effect was abolished in cultures from NPY Y1 receptor knockout mice (Y1؊͞؊). Compared with wild-type mice (Y1؉͞؉), the adrenal content and constitutive release of catecholamine were increased in chromaffin cells from Y 1؊͞؊ mice. In resting animals, catecholamine plasma concentrations were higher in Y1؊͞؊ mice. Comparing the adrenal glands of both genotypes, no differences were observed in the area of the medulla, cortex, and X zone. The high turnover of adrenal catecholamine in Y 1؊͞؊ mice was explained by the enhancement of tyrosine hydroxylase (TH) activity, although no change in the affinity of the enzyme was observed. The molecular interaction between the Y 1 receptor and TH was demonstrated by the fact that NPY markedly inhibited the forskolin-induced luciferin activity in Y 1 receptor-expressing SK-N-MC cells transfected with a TH promoter sequence. We propose that NPY controls the release and synthesis of catecholamine from the adrenal medulla and consequently contributes to the sympathoadrenal tone. (3,4). NPY is an important neurotransmitter of the sympathetic function that potentiates the catecholamine vasoconstrictor activity through the Y 1 receptor and exerts prejunctional inhibitory effects on NE release from the sympathetic nerve endings of the heart through the Y 2 receptor (5). In addition, the nerve terminals of parasympathetic neurons in the mouse heart possess Y 2 receptors, which, when activated, reduce acetylcholine release, also causing an inhibition of the parasympathetic nervous system (6). We have shown that NPY Y 1 knockout mice (Y 1 Ϫ͞Ϫ) lose their ability to potentiate NE-induced vasoconstriction and have normal blood pressure, probably indicating a minor role of NPY in the maintenance of blood pressure homeostasis (7). Recently, these mice were investigated for their cardiac sympathovagal balance in baseline conditions and during an acute social challenge. Reduced somatomotor activity during nonsocial challenges, lower heart rate in baseline conditions, and larger heart rate responsiveness during social defeat were reported (8). Besides its presence in nerve endings, NPY is produced by chromaffin cells of adrenal medulla of different species, including human (9). The mouse has higher adrenal NPY content than rat, pig, or humans (10, 11). The effect of NPY on the adrenal medulla is controversial. NPY stimulated catecholamine release from intact rat adrenal capsular tissue (12), although an inhibitory effect of NPY on catecholamine secretion in rat adrenomedullary primary cell cultures was also observed (13). Moreover, there is a weak inhibitory effect of NPY on NE and epinephrine (EP) release from bovine chromaffin cells, evoked by addition of a cholinergic agonist (14, 15). However, depending on the experimental conditions, conflicting results wer...

Neuropeptide Y (NPY) is a 36 amino acid peptide widely present in the CNS, including the retina. Previous studies have demonstrated that NPY promotes cell proliferation of rat post‐natal hippocampal and olfactory epithelium precursor cells. The aim of this work was to investigate the role of NPY on cell proliferation of rat retinal neural cells. For this purpose, primary retinal cell cultures expressing NPY, and NPY Y1, Y2, Y4 and Y5 receptors [Álvaro et al., (2007) Neurochem. Int., 50, 757] were used. NPY (10–1000 nM) stimulated cell proliferation through the activation of NPY Y1, Y2 and Y5 receptors. NPY also increased the number of proliferating neuronal progenitor cells (BrdU+/nestin+ cells). The intracellular mechanisms coupled to NPY receptors activation that mediate the increase in cell proliferation were also investigated. The stimulatory effect of NPY on cell proliferation was reduced by l‐nitroarginine‐methyl‐esther (l‐NAME; 500 μM), a nitric oxide synthase inhibitor, 1H‐[1,2,4]oxadiazolo‐[4, 3‐a]quinoxalin‐1‐one (ODQ; 20 μM), a soluble guanylyl cyclase inhibitor or U0126 (1 μM), an inhibitor of the extracellular signal‐regulated kinase 1/2 (ERK 1/2). In conclusion, NPY stimulates retinal neural cell proliferation, and this effect is mediated through nitric oxide–cyclic GMP and ERK 1/2 pathways.

MEDICINE 2012;1:783-791

NPY is present in the retina of different species but its role is not elucidated yet. In this work, using different rat retina in vitro models

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Neuropeptide Y (NPY) produced by arcuate nucleus (ARC) neurons has a strong orexigenic effect on target neurons. Hypothalamic NPY levels undergo wide-ranging oscillations during the circadian cycle and in response to fasting and peripheral hormones (from 0.25 to 10-fold change). The aim of the present study was to evaluate the impact of a moderate long-term modulation of NPY within the ARC neurons on food consumption, body weight gain and hypothalamic neuropeptides. We achieved a physiological overexpression (3.6-fold increase) and down-regulation (0.5-fold decrease) of NPY in the rat ARC by injection of AAV vectors expressing NPY and synthetic microRNA that target the NPY, respectively. Our work shows that a moderate overexpression of NPY was sufficient to induce diurnal over-feeding, sustained body weight gain and severe obesity in adult rats. Additionally, the circulating levels of leptin were elevated but the immunoreactivity (ir) of ARC neuropeptides was not in accordance (POMC-ir was unchanged and AGRP-ir increased), suggesting a disruption in the ability of ARC neurons to response to peripheral metabolic alterations. Furthermore, a dysfunction in adipocytes phenotype was observed in these obese rats. In addition, moderate down-regulation of NPY did not affect basal feeding or normal body weight gain but the response to food deprivation was compromised since fasting-induced hyperphagia was inhibited and fasting-induced decrease in locomotor activity was absent.These results highlight the importance of the physiological ARC NPY levels oscillations on feeding regulation, fasting response and body weight preservation, and are important for the design of therapeutic interventions for obesity that include the NPY.