Interactions between the regulatory peptide 26RFa (QRFP) and insulin in the regulation of glucose homeostasis in two complementary models: The high fat 26RFa-deficient mice and the streptozotocin insulin-deficient mice.

The regulatory peptide 26RFa (QRFP) is involved in the control of glucose homeostasis at the periphery by acting as an incretin, and in the brain by mediating the central antihyperglycemic effect of insulin, indicating the occurrence of a close relationship between 26RFa and insulin in the regulation of glucose metabolism. Here, we investigated the physiological interactions between 26RFa and insulin in two complementary models i.e. a model of obese/hyperglycemic mice deficient for 26RFa and a model of diabetic mice deficient for insulin. For this, transgenic 26RFa-deficient mice were made obese and chronically hyperglycemic by a 3-month high fat diet (HFD) and second group of mice was made diabetic by destruction of the ß cells of the pancreatic islets using a single injection of streptozotocin. Our data reveal that 26RFa deficiency does not impact significantly the "glycemic" phenotype of the HFD mice. The pancreatic islets, liver, white adipose tissue masses are not altered by the lack of 26RFa production but the brown adipose tissue (BAT) weight is significantly increased in these animals. In diabetic insulin-deficient mice, the injection of 26RFa does not exhibit any beneficial effect on the impaired glucose homeostasis characterizing this model. Finally, we show that streptozotocin diabetic mice display lowered plasma 26RFa levels as compared to untreated mice, whereas the expression of the peptide in the duodenum is not affected. Taken together, the present results indicate that dysregulation of glucose homeostasis in obese/hyperglycemic mice is not aggravated by the absence of 26RFa that may be compensated by the increase of BAT mass. In diabetic insulin-deficient mice, the antihypergycemic effect of 26RFa is totally blunted probably as a result of the impaired insulin production characterizing this model, avoiding therefore the action of the peptide.

The 26RFa (QRFP)/GPR103 neuropeptidergic system in mice relays insulin signalling into the brain to regulate glucose homeostasis.

AIMS/HYPOTHESIS: 26RFa (pyroglutamilated RFamide peptide [QRFP]) is a biologically active peptide that regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity at the periphery. 26RFa is also produced by a neuronal population localised in the hypothalamus. In this study we investigated whether 26RFa neurons are involved in the hypothalamic regulation of glucose homeostasis. METHODS: 26Rfa+/+, 26Rfa-/- and insulin-deficient male C57Bl/6J mice were used in this study. Mice received an acute intracerebroventricular (i.c.v.) injection of 26RFa, insulin or the 26RFa receptor (GPR103) antagonist 25e and were subjected to IPGTTs, insulin tolerance tests, acute glucose-stimulated insulin secretion tests and pyruvate tolerance tests (PTTs). Secretion of 26RFa by hypothalamic explants after incubation with glucose, leptin or insulin was assessed. Expression and quantification of the genes encoding 26RFa, agouti-related protein, the insulin receptor and GPR103 were evaluated by quantitative reverse transcription PCR and RNAscope in situ hybridisation. RESULTS: Our data indicate that i.c.v.-injected 26RFa induces a robust antihyperglycaemic effect associated with an increase in insulin production by the pancreatic islets. In addition, we found that insulin strongly stimulates 26Rfa expression and secretion by the hypothalamus. RNAscope experiments revealed that neurons expressing 26Rfa are mainly localised in the lateral hypothalamic area, that they co-express the gene encoding the insulin receptor and that insulin induces the expression of 26Rfa in these neurons. Concurrently, the central antihyperglycaemic effect of insulin is abolished in the presence of a GPR103 antagonist and in 26RFa-deficient mice. Finally, our data indicate that the hypothalamic 26RFa neurons are not involved in the central inhibitory effect of insulin on hepatic glucose production, but mediate the central effects of the hormone on its own peripheral production. CONCLUSION/INTERPRETATION: We have identified a novel mechanism in the hypothalamic regulation of glucose homeostasis, the 26RFa/GPR103 system, and we provide evidence that this neuronal peptidergic system is a key relay for the central regulation of glucose metabolism by insulin.

Acute but Not Chronic Central Administration of the Neuropeptide 26RFa (QRFP) Improves Glucose Homeostasis in Obese/Diabetic Mice.

INTRODUCTION: The aim of the study is to investigate whether acute or chronic central administration of the hypothalamic neuropeptide 26RFa may ameliorate the glycemic control of obese/diabetic mice. METHODS: Mice were treated for 4 months with a high-fat (HF) diet and received a single i.c.v. injection of 26RFa (3 µg) or a chronic i.c.v. administration of the peptide during 28 days via osmotic minipumps (25 µg/day). i.p. and oral glucose (GLU) tolerance tests, insulin (INS) tolerance test, glucose-stimulated insulin secretion (GSIS), food/water intake, horizontal/vertical activity, energy expenditure, meal pattern, and whole-body composition were monitored. In addition, 26RFa and GPR103 mRNA expressions as well as plasma 26RFa levels were evaluated by RT-QPCR and radioimmunoassay. RESULTS: Acute administration of 26RFa in HF mice induced a robust antihyperglycemic effect by enhancing INS secretion, whereas chronic administration of the neuropeptide is unable to improve glucose homeostasis in these obese/diabetogenic conditions. By contrast, chronic 26RFa treatment induced an increase of the body weight accompanied with an enhanced food intake and a decreased energy expenditure. Finally, we show that the HF diet does not alter the hypothalamic expression of the 26RFa/GPR103 neuropeptidergic system nor the levels of circulating 26RFa. CONCLUSION: Our data indicate that the central beneficial effect of 26RFa on glucose homeostasis, by potentiating GSIS, is preserved in HF mice. However, chronic administration of the neuropeptide is unable to balance glycemia in these pathophysiological conditions, suggesting that the hypothalamic 26RFa/GPR103 neuropeptidergic system mainly affects short-term regulation of glucose metabolism.

Effect of Neuroprotective Magnesium Sulfate Treatment on Brain Transcription Response to Hypoxia Ischemia in Neonate Mice.

MgSO4 is widely used in the prevention of preterm neurological disabilities but its modes of action remain poorly established. We used a co-hybridization approach using the transcriptome in 5-day old mice treated with a single dose of MgSO4 (600 mg/kg), and/or exposed to hypoxia-ischemia (HI). The transcription of hundreds of genes was altered in all the groups. MgSO4 mainly produced repressions culminating 6 h after injection. Bio-statistical analysis revealed the repression of synaptogenesis and axonal development. The putative targets of MgSO4 were Mnk1 and Frm1. A behavioral study of adults did not detect lasting effects of neonatal MgSO4 and precluded NMDA-receptor-mediated side effects. The effects of MgSO4 plus HI exceeded the sum of the effects of separate treatments. MgSO4 prior to HI reduced inflammation and the innate immune response probably as a result of cytokine inhibition (Ccl2, Ifng, interleukins). Conversely, MgSO4 had little effect on HI-induced transcription by RNA-polymerase II. De novo MgSO4-HI affected mitochondrial function through the repression of genes of oxidative phosphorylation and many NAD-dehydrogenases. It also likely reduced protein translation by the repression of many ribosomal proteins, essentially located in synapses. All these effects appeared under the putative regulatory MgSO4 induction of the mTORC2 Rictor coding gene. Lasting effects through Sirt1 and Frm1 could account for this epigenetic footprint.

Cell-penetrating, antioxidant SELENOT mimetic protects dopaminergic neurons and ameliorates motor dysfunction in Parkinson's disease animal models.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor dysfunction for which there is an unmet need for better treatment options. Although oxidative stress is a common feature of neurodegenerative diseases, notably PD, there is currently no efficient therapeutic strategy able to tackle this multi-target pathophysiological process. Based on our previous observations of the potent antioxidant and neuroprotective activity of SELENOT, a vital thioredoxin-like selenoprotein, we designed the small peptide PSELT from its redox active site to evaluate its antioxidant properties in vivo, and its potential polyfunctional activity in PD models. PSELT protects neurotoxin-treated dopaminergic neurons against oxidative stress and cell death, and their fibers against neurotoxic degeneration. PSELT is cell-permeable and acts in multiple subcellular compartments of dopaminergic neurons that are vulnerable to oxidative stress. In rodent models of PD, this protective activity prevented neurodegeneration, restored phosphorylated tyrosine hydroxylase levels, and led to improved motor skills. Transcriptomic analysis revealed that gene regulation by PSELT after MPP+ treatment negatively correlates with that occurring in PD, and positively correlates with that occurring after resveratrol treatment. Mechanistically, a major impact of PSELT is via nuclear stimulation of the transcription factor EZH2, leading to neuroprotection. Overall, these findings demonstrate the potential of PSELT as a therapeutic candidate for treatment of PD, targeting oxidative stress at multiple intracellular levels.

Urantide Improves Cardiac Function, Modulates Systemic Cytokine Response, and Increases Survival in A Murine Model of Endotoxic Shock.

INTRODUCTION: Urotensin II is a potent vasoactive peptide activating the the G protein-coupled urotensin II receptor UT, and is involved in systemic inflammation and cardiovascular functions. The aim of our work was to study the impact of the UT antagonist urantide on survival, systemic inflammation, and cardiac function during endotoxic shock. METHODS: C57Bl/6 mice were intraperitoneally injected with lipopolysaccharide (LPS) and then randomized to be injected either by urantide or NaCl 0.9% 3, 6, and 9 h (H3, H6, H9) after LPS. The effect of urantide on the survival rate, the levels of cytokines in plasma at H6, H9, H12, the expression level of nuclear factor-kappa B (NF-κB-p65) in liver and kidney (at H12), and the cardiac function by trans-thoracic echocardiography from H0 to H9 was evaluated. RESULTS: Urantide treatment improved survival (88.9% vs. 30% on day 6, P < 0.05). This was associated with changes in cytokine expression: a decrease in IL-6 (2,485 [2,280-2,751] pg/mL vs. 3,330 [3,119-3,680] pg/mL, P < 0.01) at H6, in IL-3 (1.0 [0.40-2.0] pg/mL vs. 5.8 [3.0-7.7] pg/mL, P < 0.01), and IL-1ß (651 [491-1,135] pg/mL vs. 1,601 [906-3,010] pg/mL, P < 0.05) at H12 after LPS administration. Urantide decreased the proportion of cytosolic NF-κB-p65 in liver (1.3 [0.9-1.9] vs. 3.2 [2.3-4], P < 0.01) and kidney (0.3 [0.3-0.4] vs. 0.6 [0.5-1.1], P < 0.01). Urantide improved cardiac function (left ventricular fractional shortening: 24.8 [21.5-38.9] vs. 12.0 [8.7-17.6] %, P < 0.01 and cardiac output: 30.3 [25.9-39.8] vs. 15.1 [13.0-16.9] mL/min, P < 0.0001). CONCLUSION: These results show a beneficial curative role of UT antagonism on cytokine response (especially IL-3), cardiac dysfunction, and survival during endotoxic shock in mice, highlighting a potential new therapeutic target for septic patients.

Neonatal cerebral hypoxia-ischemia in mice triggers age-dependent vascular effects and disabilities in adults; implication of tissue plasminogen activator (tPA).

Neonatal encephalopathy frequently results from hypoxia-ischemia (HI) or inflammation in preterm or term neonates. Neuropathology depends on cerebral development at insult time, but the poor correlation of neuromotor, cognitive, and behavioral disabilities in infancy with initial imaging and clinical records precludes early prognosis. The Rice-Vannucci HI procedure was applied to wild type and tissue plasminogen activator knockout (tPA-KO) mice as surrogates for human preterm (with five-day-old postnatal (P5) mice) or human term (with ten-day-old postnatal (P10) mice). Acute and delayed T2-magnetic resonance imaging (T2-MRI) signals and cognitive deficits in adulthood (spatial memory and social interaction) were investigated in the same animals. Early vascular tPA and matrix metalloproteinase-9 (MMP-9) activities, blood-brain barrier permeability to water or IgG, and microglial activation were assessed separately. HI in P5 or P10 mice induced early hemisphere swelling in T2-MRI scans, and a delayed atrophy of the cortex and hippocampus, but affected white matter in the P5 group only, irrespective of the wild type or tPA-KO genotype. Adults had no motor disabilities, but we did find HI-induced age-dependent deficits, preferentially social interaction and activity in P5 mice, and spatial learning in P10 mice. In P5 mice, tPA-KO prevented MMP-9 activation, IgG extravasation, microglial activation, and behavior impairments. In P10 mice, MMP-9 activation and inflammatory processes remained in the hippocampus of the tPA-KO group, and also contributed to persistent spatial learning deficits. Perinatal HI in mice mimicked the unpredictability of outcomes from imaging in human clinics. Delayed deficits appeared associated to vascular dysfunction-induced inflammation, which recalls our previous work showing major vascular maturation between P5 and P10 stages. Using omics to explore neural, glial, or brain vessel markers in neonate blood may be a promising perspective to identify pertinent prognostic tools.

The neuropeptide 26RFa in the human gut and pancreas: potential involvement in glucose homeostasis.

OBJECTIVE: Recent studies performed in mice revealed that the neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and by increasing insulin sensitivity. However, in humans, an association between 26RFa and the regulation of glucose homeostasis is poorly documented. In this study, we have thus investigated in detail the distribution of 26RFa and its receptor, GPR103, in the gut and the pancreas, and determined the response of this peptidergic system to an oral glucose challenge in obese patients. DESIGN AND METHODS: Distribution of 26RFa and GPR103 was examined by immunohistochemistry using gut and pancreas tissue sections. Circulating 26RFa was determined using a specific radioimmunoassay in plasma samples collected during an oral glucose tolerance test. RESULTS: 26RFa and GPR103 are present all along the gut but are more abundant in the stomach and duodenum. In the stomach, the peptide and its receptor are highly expressed in the gastric glands, whereas in the duodenum, ileum and colon they are present in the enterocytes and the goblet cells. In the pancreatic islets, the 26RFa/GPR103 system is mostly present in the ß cells. During an oral glucose tolerance test, plasma 26RFa profile is different between obese patients and healthy volunteers, and we found strong positive correlations between 26RFa blood levels and the BMI, and with various parameters of insulin secretion and insulin resistance. CONCLUSION: The present data suggest an involvement of the 26RFa/GPR103 peptidergic system in the control of human glucose homeostasis.

Neuropeptide 26RFa (QRFP) is a key regulator of glucose homeostasis and its activity is markedly altered in obese/hyperglycemic mice.

Recent studies have shown that the hypothalamic neuropeptide 26RFa regulates glucose homeostasis by acting as an incretin and increasing insulin sensitivity. In this study, we further characterized the role of the 26RFa/GPR103 peptidergic system in the global regulation of glucose homeostasis using a 26RFa receptor antagonist and also assessed whether a dysfunction of the 26RFa/GPR103 system occurs in obese hyperglycemic mice. First, we demonstrate that administration of the GPR103 antagonist reduces the global glucose-induced incretin effect and insulin sensitivity whereas, conversely, administration of exogenous 26RFa attenuates glucose-induced hyperglycemia. Using a mouse model of high-fat diet-induced obesity and hyperglycemia, we found a loss of the antihyperglcemic effect and insulinotropic activity of 26RFa, accompanied with a marked reduction of its insulin-sensitive effect. Interestingly, this resistance to 26RFa is associated with a downregulation of the 26RFa receptor in the pancreatic islets, and insulin target tissues. Finally, we observed that the production and release kinetics of 26RFa after an oral glucose challenge is profoundly altered in the high-fat mice. Altogether, the present findings support the view that 26RFa is a key regulator of glucose homeostasis whose activity is markedly altered under obese/hyperglycemic conditions.

Dysregulation of Aldosterone Secretion in Mast Cell-Deficient Mice.

Resident adrenal mast cells have been shown to activate aldosterone secretion in rat and man. Especially, mast cell proliferation has been observed in adrenal tissues from patients with aldosterone-producing adrenocortical adenoma. In the present study, we show that the activity of adrenal mast cells is stimulated by low-sodium diet and correlates with aldosterone synthesis in C57BL/6 and BALB/c mice. We have also investigated the regulation of aldosterone secretion in mast cell-deficient C57BL/6 KitW-sh/W-sh mice in comparison with wild-type C57BL/6 mice. KitW-sh/W-sh mice submitted to normal sodium diet had basal plasma aldosterone levels similar to those observed in wild-type animals. Conversely, low-sodium diet unexpectedly induced an exaggerated aldosterone response, which seemed to result from an increase in adrenal renin and angiotensin type 1 receptor expression. Severe hyperaldosteronism was associated with an increase in systolic blood pressure and marked hypokalemia, which favored polyuria. Adrenal renin and angiotensin type 1 receptor overexpression may represent a compensatory mechanism aimed at activating aldosterone production in the absence of mast cells. Finally, C57BL/6 KitW-sh/W-sh mice represent an unexpected animal model of primary aldosteronism, which has the particularity to be triggered by sodium restriction.

The Neuropeptide 26RFa (QRFP) and Its Role in the Regulation of Energy Homeostasis: A Mini-Review.

This mini-review deals with the neuropeptide 26RFa (or QRFP) which is a member of the RFamide peptide family discovered simultaneously by three groups in 2003. 26RFa (or its N-extended form 43RFa) was subsequently shown to be the endogenous ligand of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and at the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when injected centrally, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting that the 26RFa/GPR103 system may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic ß cell death and apoptosis. This brief overview reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

Selenoprotein T Exerts an Essential Oxidoreductase Activity That Protects Dopaminergic Neurons in Mouse Models of Parkinson's Disease.

AIMS: Oxidative stress is central to the pathogenesis of Parkinson's disease (PD), but the mechanisms involved in the control of this stress in dopaminergic cells are not fully understood. There is increasing evidence that selenoproteins play a central role in the control of redox homeostasis and cell defense, but the precise contribution of members of this family of proteins during the course of neurodegenerative diseases is still elusive. RESULTS: We demonstrated first that selenoprotein T (SelT) whose gene disruption is lethal during embryogenesis, exerts a potent oxidoreductase activity. In the SH-SY5Y cell model of dopaminergic neurons, both silencing and overexpression of SelT affected oxidative stress and cell survival. Treatment with PD-inducing neurotoxins such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) or rotenone triggered SelT expression in the nigrostriatal pathway of wild-type mice, but provoked rapid and severe parkinsonian-like motor defects in conditional brain SelT-deficient mice. This motor impairment was associated with marked oxidative stress and neurodegeneration and decreased tyrosine hydroxylase activity and dopamine levels in the nigrostriatal system. Finally, in PD patients, we report that SelT is tremendously increased in the caudate putamen tissue. INNOVATION: These results reveal the activity of a novel selenoprotein enzyme that protects dopaminergic neurons against oxidative stress and prevents early and severe movement impairment in animal models of PD. CONCLUSIONS: Our findings indicate that selenoproteins such as SelT play a crucial role in the protection of dopaminergic neurons against oxidative stress and cell death, providing insight into the molecular underpinnings of this stress in PD.

Selenoprotein T Deficiency Leads to Neurodevelopmental Abnormalities and Hyperactive Behavior in Mice.

Selenoprotein T (SelT) is a newly discovered thioredoxin-like protein, which is abundantly but transiently expressed in the neural lineage during brain ontogenesis. Because its physiological function in the brain remains unknown, we developed a conditional knockout mouse line (Nes-Cre/SelTfl/fl) in which SelT gene is specifically disrupted in nerve cells. At postnatal day 7 (P7), these mice exhibited reduced volume of different brain structures, including hippocampus, cerebellum, and cerebral cortex. This phenotype, which is observed early during the first postnatal week, culminated at P7 and was associated with increased loss of immature neurons but not glial cells, through apoptotic cell death. This phenomenon was accompanied by elevated levels of intracellular reactive oxygen species, which may explain the increased neuron demise and reduced brain structure volumes. At the second postnatal week, an increase in neurogenesis was observed in the cerebellum of Nes-Cre/SelTfl/fl mice, suggesting the occurrence of developmental compensatory mechanisms in the brain. In fact, the brain volume alterations observed at P7 were attenuated in adult mice. Nevertheless, SelT mutant mice exhibited a hyperactive behavior, suggesting that despite an apparent morphological compensation, SelT deficiency leads to cerebral malfunction in adulthood. Altogether, these results demonstrate that SelT exerts a neuroprotective role which is essential during brain development, and that its loss impairs mice behavior.

[The neuropeptide 26RFa and its role in the regulation of energy metabolism]. / Le neuropeptide 26RFa : un nouveau régulateur de l'homéostasie énergétique.

The neuropeptide 26RFa, also referred to as QRFP (for pyroglutamilated RFamide peptide), is the latest member of the RFamide peptide family to be discovered. 26RFa and its N-extended form, 43RFa, have been characterized in all vertebrate classes as the endogenous ligands of the human orphan receptor GPR103. In the brain, 26RFa and GPR103mRNA are primarily expressed in hypothalamic nuclei involved in the control of feeding behavior, and in the periphery, the neuropeptide and its receptor are present in abundance in the gut and the pancreatic islets, suggesting that 26RFa is involved in the regulation of energy metabolism. Indeed, 26RFa stimulates food intake when centrally injected, and its orexigenic effect is even more pronounced in obese animals. The expression of 26RFa is up-regulated in the hypothalamus of obese animals, supporting the view that 26RFa may play a role in the development and/or maintenance of the obese status. Recent data indicate that 26RFa is also involved in the regulation of glucose homeostasis. 26RFa reduces glucose-induced hyperglycemia, increases insulin sensitivity and insulinemia. Furthermore, an oral ingestion of glucose strongly stimulates 26RFa release by the gut, indicating that 26RFa is a novel incretin. Finally, 26RFa is able to prevent pancreatic ß cell death and apoptosis. In conclusion, this overview of the literature reveals that 26RFa is a key neuropeptide in the regulation of energy metabolism. Further fields of research are suggested including the pathophysiological implication of the 26RFa/GPR103 system.

Hypothalamic Neuropeptide 26RFa Acts as an Incretin to Regulate Glucose Homeostasis.

26RFa is a hypothalamic neuropeptide that promotes food intake. 26RFa is upregulated in obese animal models, and its orexigenic activity is accentuated in rodents fed a high-fat diet, suggesting that this neuropeptide might play a role in the development and maintenance of the obese status. As obesity is frequently associated with type 2 diabetes, we investigated whether 26RFa may be involved in the regulation of glucose homeostasis. In the current study, we show a moderate positive correlation between plasma 26RFa levels and plasma insulin in patients with diabetes. Plasma 26RFa concentration also increases in response to an oral glucose tolerance test. In addition, we found that 26RFa and its receptor GPR103 are present in human pancreatic ß-cells as well as in the gut. In mice, 26RFa attenuates the hyperglycemia induced by a glucose load, potentiates insulin sensitivity, and increases plasma insulin concentrations. Consistent with these data, 26RFa stimulates insulin production by MIN6 insulinoma cells. Finally, we show, using in vivo and in vitro approaches, that a glucose load induces a massive secretion of 26RFa by the small intestine. Altogether, the present data indicate that 26RFa acts as an incretin to regulate glucose homeostasis.

Temporal analysis of free exploration of an elevated plus-maze in mice.

The elevated plus-maze (EPM) is a very common rodent test of anxiety. It is based on an approach-avoidance conflict between secure closed arms and aversive open arms. However, discrepancies remain on the interpretation of animals' behavior in this assay. The purpose of our study was to get a better understanding of the mouse behavior in the EPM. We applied a minute-by-minute analysis to compare the behavior of mice forcibly exposed to the maze or set free to explore the maze from a familiar box. Three strains of mice (CD1, BALB/c, and C57Bl/6) were tested. The combination of our different conditions of the test with the minute-by-minute analysis showed that mice did not avoid open arms during the first 2 min of the test when they were forcibly exposed to the EPM. Conversely, free exploration of the EPM resulted in a pattern of behavior characterized by open arm avoidance from the outset, demonstrating that open arm avoidance in mice is unconditioned. These findings generalize across the 3 mouse strains. These data suggest that rodents enter the open arms to complete spatial information about the apparatus as a whole before their natural tendency to avoid them is expressed. Our data also indicate that a detailed behavioral analysis is needed whenever BALB/c mice are to be exposed by force to the EPM. Further studies are required to fully understand the behavior of rodents in the EPM and to avoid false interpretations in the fields of psychopharmacology and behavioral neuroscience.

Concordant localization of functional urotensin II and urotensin II-related peptide binding sites in the rat brain: Atypical occurrence close to the fourth ventricle.

Urotensin II (UII) and Urotensin II-related peptide (URP) are structurally related paralog peptides that exert peripheral and central effects. UII binding sites have been partly described in brain, and those of URP have never been reported. We exhaustively compared [(125)I]-UII and -URP binding site distributions in the adult rat brain, and found that they fully overlapped at the regional level. We observed UII/URP binding sites in structures lining ventricles, comprising the sphenoid nucleus and cell rafts scattered on a line joining the fourth ventricle and its lateral recess. After injection of UII and URP in the lateral ventricle, we observed c-Fos-positive cell nuclei in areas close to the fourth ventricle, indicating that these receptors are functional. Different c-Fos-containing cell populations were activated. They were all positive for vimentin and glial fibrillary acidic protein (GFAP), excluding the possibility of an ependymal nature. In conclusion, this study demonstrated that UII and URP binding sites are totally overlapping and that these sites were functional in regions bordering the fourth ventricle. These data support a role for UII/URP at the interface between brain parenchyma and cerebrospinal fluid.

T-type channel blockade impairs long-term potentiation at the parallel fiber-Purkinje cell synapse and cerebellar learning.

CaV3.1 T-type channels are abundant at the cerebellar synapse between parallel fibers and Purkinje cells where they contribute to synaptic depolarization. So far, no specific physiological function has been attributed to these channels neither as charge carriers nor more specifically as Ca(2+) carriers. Here we analyze their incidence on synaptic plasticity, motor behavior, and cerebellar motor learning, comparing WT animals and mice where T-type channel function has been abolished either by gene deletion or by acute pharmacological blockade. At the cellular level, we show that CaV3.1 channels are required for long-term potentiation at parallel fiber-Purkinje cell synapses. Moreover, basal simple spike discharge of the Purkinje cell in KO mice is modified. Acute or chronic T-type current blockade results in impaired motor performance in particular when a good body balance is required. Because motor behavior integrates reflexes and past memories of learned behavior, this suggests impaired learning. Indeed, subjecting the KO mice to a vestibulo-ocular reflex phase reversal test reveals impaired cerebellum-dependent motor learning. These data identify a role of low-voltage activated calcium channels in synaptic plasticity and establish a role for CaV3.1 channels in cerebellar learning.

The PACAP-regulated gene selenoprotein T is abundantly expressed in mouse and human ß-cells and its targeted inactivation impairs glucose tolerance.

Selenoproteins are involved in the regulation of redox status, which affects several cellular processes, including cell survival and homeostasis. Considerable interest has arisen recently concerning the role of selenoproteins in the regulation of glucose metabolism. Here, we found that selenoprotein T (SelT), a new thioredoxin-like protein of the endoplasmic reticulum, is present at high levels in human and mouse pancreas as revealed by immunofluorescence and quantitative PCR. Confocal immunohistochemistry studies revealed that SelT is mostly confined to insulin- and somatostatin-producing cells in mouse and human islets. To elucidate the role of SelT in ß-cells, we generated, using a Cre-Lox strategy, a conditional pancreatic ß-cell SelT-knockout C57BL/6J mice (SelT-insKO) in which SelT gene disruption is under the control of the rat insulin promoter Cre gene. Glucose administration revealed that male SelT-insKO mice display impaired glucose tolerance. Although insulin sensitivity was not modified in the mutant mice, the ratio of glucose to insulin was significantly higher in the SelT-insKO mice compared with wild-type littermates, pointing to a deficit in insulin production/secretion in mutant mice. In addition, morphometric analysis showed that islets from SelT-insKO mice were smaller and that their number was significantly increased compared with islets from their wild-type littermates. Finally, we found that SelT is up-regulated by pituitary adenylate cyclase-activating polypeptide (PACAP) in ß-pancreatic cells and that SelT could act by facilitating a feed-forward mechanism to potentiate insulin secretion induced by the neuropeptide. Our findings are the first to show that the PACAP-regulated SelT is localized in pancreatic ß- and δ-cells and is involved in the control of glucose homeostasis.

Cerebellum shapes hippocampal spatial code.

Spatial representation is an active process that requires complex multimodal integration from a large interacting network of cortical and subcortical structures. We sought to determine the role of cerebellar protein kinase C (PKC)-dependent plasticity in spatial navigation by recording the activity of hippocampal place cells in transgenic L7PKCI mice with selective disruption of PKC-dependent plasticity at parallel fiber-Purkinje cell synapses. Place cell properties were exclusively impaired when L7PKCI mice had to rely on self-motion cues. The behavioral consequence of such a deficit is evidenced here by selectively impaired navigation capabilities during a path integration task. Together, these results suggest that cerebellar PKC-dependent mechanisms are involved in processing self-motion signals essential to the shaping of hippocampal spatial representation.