Growth hormone secretagogue receptor signaling in the supramammillary nucleus targets nitric oxide-producing neurons and controls recognition memory in mice

Ghrelin is a stomach-derived hormone that acts via the growth hormone secretagogue receptor (GHSR). Recent evidence suggests that some of ghrelin's actions may be mediated via the supramammillary nucleus (SuM). Not only does ghrelin bind to cells within the mouse SuM, but ghrelin also activates SuM cells and intra-SuM ghrelin administration induces feeding in rats. In the current study, we aimed to further characterize ghrelin action in the SuM. We first investigated a mouse model expressing enhanced green fluorescent protein (eGFP) under the promoter of GHSR (GHSR-eGFP mice). We found that the SuM of GHSR-eGFP mice contains a significant amount of eGFP cells, some of which express neuronal nitric oxide synthase. Centrally-, but not systemically-, injected ghrelin reached the SuM, where it induced c-Fos expression. Furthermore, a 5-day 40% calorie restriction protocol, but not a 2-day fast, increased c-Fos expression in non-eGFP+ cells of the SuM of GHSR-eGFP mice, whereas c-Fos induction by calorie restriction was not observed in GHSR-deficient mice. Exposure of satiated mice to a binge-like eating protocol also increased c-Fos expression in non-eGFP+ cells of the SuM of GHSR-eGFP mice in a GHSR-dependent manner. Finally, intra-SuM-injected ghrelin did not acutely affect food intake, locomotor activity, behavioral arousal or spatial memory but increased recognition memory. Thus, we provide a compelling neuroanatomical characterization of GHSR SuM neurons and its behavioral implications in mice.

Ghrelin treatment induces rapid and delayed increments of food intake: a heuristic model to explain ghrelin's orexigenic effects

Ghrelin is a stomach-derived peptide hormone with salient roles in the regulation of energy balance and metabolism. Notably, ghrelin is recognized as the most powerful known circulating orexigenic hormone. Here, we systematically investigated the effects of ghrelin on energy homeostasis and found that ghrelin primarily induces a biphasic effect on food intake that has indirect consequences on energy expenditure and nutrient partitioning. We also found that ghrelin-induced biphasic effect on food intake requires the integrity of Agouti-related peptide/neuropeptide Y-producing neurons of the hypothalamic arcuate nucleus, which seem to display a long-lasting activation after a single systemic injection of ghrelin. Finally, we found that different autonomic, hormonal and metabolic satiation signals transiently counteract ghrelin-induced food intake. Based on our observations, we propose a heuristic model to describe how the orexigenic effect of ghrelin and the anorectic food intake-induced rebound sculpt a timely constrain feeding response to ghrelin.

Development of Nonpeptidic Inverse Agonists of the Ghrelin Receptor (GHSR) Based on the 1,2,4-Triazole Scaffold

GHSR controls, among others, growth hormone and insulin secretion, adiposity, feeding, and glucose metabolism. Therefore, an inverse agonist ligand capable of selectively targeting GHSR and reducing its high constitutive activity appears to be a good candidate for the treatment of obesity-related metabolic diseases. In this context, we present a study that led to the development of several highly potent and selective inverse agonists of GHSR based on the 1,2,4-triazole scaffold. We demonstrate that, depending on the nature of the substituents on positions 3, 4, and 5, this scaffold leads to ligands that exert an intrinsic inverse agonist activity on GHSR-catalyzed G protein activation through the stabilization of a specific inactive receptor conformation. Thanks to an in vivo evaluation, we also show that one of the most promising ligands not only exerts an effect on insulin secretion in rat pancreatic islets but also affects the orexigenic effects of ghrelin in mice.

Growth hormone secretagogue receptor in dopamine neurons controls appetitive and consummatory behaviors towards high-fat diet in ad-libitum fed mice

Growth hormone secretagogue receptor (GHSR), the receptor for ghrelin, is expressed in key brain nuclei that regulate food intake. The dopamine (DA) pathways have long been recognized to play key roles mediating GHSR effects on feeding behaviors. Here, we aimed to determine the role of GHSR in DA neurons controlling appetitive and consummatory behaviors towards high fat (HF) diet. For this purpose, we crossed reactivable GHSR-deficient mice with DA transporter (DAT)-Cre mice, which express Cre recombinase under the DAT promoter that is active exclusively in DA neurons, to generate mice with GHSR expression limited to DA neurons (DAT-GHSR mice). We found that DAT-GHSR mice show an increase of c-Fos levels in brain areas containing DA neurons after ghrelin treatment, in a similar fashion as seen in wild-type mice; however, they did not increase food intake or locomotor activity in response to systemically- or centrally-administered ghrelin. In addition, we found that satiated DAT-GHSR mice displayed both anticipatory activity to scheduled HF diet exposure and HF intake in a binge-like eating protocol similar to those in wild-type mice, whereas GHSR-deficient mice displayed impaired responses. We conclude that GHSR expression in DA neurons is sufficient to both mediate increased anticipatory activity to a scheduled HF diet exposure and fully orchestrate binge-like HF intake, but it is insufficient to restore the acute orexigenic or locomotor effects of ghrelin treatment. Thus, GHSR in DA neurons affects appetitive and consummatory behaviors towards HF diet that take place in the absence of caloric needs.

Development of a novel fluorescent ligand of growth hormone secretagogue receptor based on the N-Terminal Leap2 region

Liver-expressed antimicrobial peptide 2 (LEAP2) was recently recognized as an endogenous ligand for the growth hormone secretagogue receptor (GHSR), which also is a receptor for the hormone ghrelin. LEAP2 blocks ghrelin-induced activation of GHSR and inhibits GHSR constitutive activity. Since fluorescence-based imaging and pharmacological analyses to investigate the biology of GHSR require reliable probes, we developed a novel fluorescent GHSR ligand based on the N-terminal LEAP2 sequence, hereafter named F-LEAP2. In vitro, F-LEAP2 displayed binding affinity and inverse agonism to GHSR similar to LEAP2. In a heterologous expression system, F-LEAP2 labeling was specifically observed in the surface of GHSR-expressing cells, in contrast to fluorescent ghrelin labeling that was mainly observed inside the GHSR-expressing cells. In mice, centrally-injected F-LEAP2 reduced ghrelin-induced food intake, in a similar fashion to LEAP2, and specifically labeled cells in GHSR-expressing brain areas. Thus, F-LEAP2 represents a valuable tool to study the biology of GHSR in vitro and in vivo.

Inter-individual Variability for High Fat Diet Consumption in Inbred C57BL/6 Mice

Since inbred C57BL/6 mice are known to show inter-individual phenotypic variability for some traits, we tested the hypothesis that inbred C57BL/6 mice display a different tendency to consume a high fat (HF) diet. For this purpose, we used a compilation of HF intake data from an experimental protocol in which satiated mice were exposed to a HF pellet every morning for 2-h over 4 consecutive days. We found that mice displayed a large degree of variability in HF intake. Since day 1 HF intake significantly correlated with HF intake in successive days, we applied a hierarchical clustering algorithm on HF intake measurements in days 2, 3, and 4 in order to classify mice into “low” or “high” HF intake groups. “Low” HF intake group showed a day 1 HF intake similar to that seen in mice exposed to regular chow, while “high” HF intake group showed a higher day 1 HF intake as compared to “low” HF intake group. Both groups of mice increased HF consumption over the successive days, but “high” HF intake group always displayed a higher HF consumption than the “low” HF intake group. As compared to “low” HF intake group, “high” HF intake group showed a higher number of dopamine neurons positive for c-Fos in the VTA after the last event of HF intake. Thus, inbred C57BL/6 mice show inter-individual variability for HF intake and such feature may be linked to a different response to the rewarding properties of the HF diet.

Growth hormone regulates neuroendocrine responses to weight loss via AgRP neurons

Weight loss triggers important metabolic responses to conserve energy, especially via the fall in leptin levels. Consequently, weight loss becomes increasingly difficult with weight regain commonly occurring in most dieters. Here we show that central growth hormone (GH) signaling also promotes neuroendocrine adaptations during food deprivation. GH activates agouti-related protein (AgRP) neurons and GH receptor (GHR) ablation in AgRP cells mitigates highly characteristic hypothalamic and metabolic adaptations induced by weight loss. Thus, the capacity of mice carrying an AgRP-specific GHR ablation to save energy during food deprivation is impaired, leading to increased fat loss. Additionally, administration of a clinically available GHR antagonist (pegvisomant) attenuates the fall of whole-body energy expenditure of food-deprived mice, similarly as seen by leptin treatment. Our findings indicate GH as a starvation signal that alerts the brain about energy deficiency, triggering key adaptive responses to conserve limited fuel stores.

Reduction in food intake elicits neuroendocrine adaptations to counterregulate the negative energy balance, e.g. via reduction in leptin levels. Here, the authors identify an additional starvation signal, growth hormone (GH). Blocking GH receptor attenuates the fall of whole body energy expenditure during food deprivation in mice.

Angiotensin II signaling to phospholipase D in renal microvascular smooth muscle cells in SHR

Angiotensin II (Ang II)-induced phospholipase D (PLD) activity is greater in aortic smooth muscle from spontaneously hypertensive rats (SHR) versus normotensive Wistar-Kyoto rats (WKY). Whether and how this signaling pathway is altered in preglomerular microvascular smooth muscle cells (PGSMCs), a cell type that may participate in genetic hypertension, is unknown. The goals of the present study were to determine in SHR and WKY PGSMCs the following: (1) whether Ang II induces PLD activity; (2) whether the effect of Ang II on PLD activity is greater in SHR; (3) which PLD isoform is stimulated by Ang II; (4) what signaling pathway mediates Ang II-induced PLD stimulation; and (5) whether the signaling pathways mediating Ang II-induced PLD activity are different in SHR and WKY. The EC(50) for Ang II-induced PLD stimulation in SHR was 10-fold lower than the EC(50) in WKY, and both were inhibited by L-158,805, an AT(1) antagonist. Inhibitors of phosphoinositol-3-kinase and protein kinase C did not block Ang II-induced PLD activity in SHR and WKY PGSMCs. Catalytically-inactive constructs of PLD2 and RhoA, but not PLD1, ADP ribosylation factor 1 (ARF1), ARF6, or ADP ribosylation factor nucleotide exchange factor (ARNO) blocked Ang II-induced PLD activity in SHR and WKY PGSMCs. Brefeldin A completely blocked Ang II-induced PLD activity in SHR but only slightly reduced Ang II-induced PLD activity in WKY PGSMCs. Therefore, we conclude that in PGSMCs, the effect of Ang II on PLD activity is (1) greater in SHR; (2) mediated by AT(1) receptors signaling to PLD2; (3) transduced primarily by Rho proteins; and (4) inhibited in SHR by brefeldin A.

Accuracy of three corrective techniques for implant bar fabrication

STATEMENT OF THE PROBLEM

Numerous articles emphasize the importance of passivity of implant-prosthetic component interfaces. Nonpassive interfaces can lead to bone loss, abutment fracture, and connecting screw breakage.

PURPOSE

The purpose of this study was to evaluate 3 postcasting techniques for the correction of non-passive fit between a cast bar superstructure and its interface with an implant abutment.

MATERIAL AND METHODS

Thirty implant Hader bars were fabricated based on a metal model composed of two 3.8/4.5 HL PME titanium implant abutments. Initial measurements were collected on the y-axis of the left implant abutment-bar interface by using a M2001ARS toolmaker microscope. Means were calculated from buccal, distal, and lingual measurements on each specimen. Ten specimens were sectioned, indexed, and corrected by casting the same alloy (group 1). Ten specimens were sectioned, indexed, and corrected by soldering (group 2). The last 10 specimens were submitted to 2 cycles of electrical discharge machining on a MedArc M-2 EDM machine (group 3). Postcorrection measurements were collected on the 3 groups. A 1-way ANOVA and a Tukey-Kramer test at a 0.05 significance level were performed on the 3 groups after the corrective techniques.

RESULTS

Initial gap means were 192 microm for group 1, 190 microm for group 2, and 198 microm for group 3. There was a significant difference (P<0.05) in gap means between group 1 (15 microm) and group 2 (72 microm) as well as between group 2 and group 3 (7.5 microm) after each correction technique. No difference was detected between group 1 and group 3.

CONCLUSION

The electrical discharge machining group resulted in the smallest mean gap distance of 7.5 microm, thus meeting the criteria of passive fit (within 10 microm) described in the literature.

Protein kinase C inhibition blocks the early appearance of vestibular compensation

This study tests the hypothesis that activation of protein kinase C (PKC) is a critical step for early recovery from spontaneous nystagmus after unilateral ablation of the vestibular periphery. Halothane-NO(2)-O(2)-anesthetized Long-Evans rats received a 5-microl intracerebroventricular bolus of vehicle (distilled water, six rats), PKC inhibitor [Iso-H-7 (10 mM, four rats; 50 mM, five rats) or bisindolemaleimide I (Bis-I, 10 microM six rats)], PKG and PKA inhibitor (A-3, 1 mM, six rats), or the serine-threonine protein kinase inhibitor H-7 (1 mM, five rats; 10 mM, five rats). Surgical unilateral labyrinthectomy (UL) was completed within 15 min. Sham control groups showed no nystagmus. Bis-I and Iso-H-7 significantly retarded the disappearance of spontaneous nystagmus quick phases for 8 h after UL (p<0.05). The effects of Iso-H-7 were dose-dependent: more nystagmus quick phases (p<0.05) were present in the 50 mM than the 10 mM group at 7 and 8 h post-UL. The rats given A-3 showed a delayed retardation of nystagmus loss, which differed significantly (p<0.05) from controls at 4-8 h after labyrinthectomy. The number of nystagmus quick phases was significantly greater than controls (p<0. 05) in the 10 mM H-7 group at 4, 5, 6 and 48 h post-UL, but only at 6 and 24 h post-UL in the 1 mM H-7 group. Thus, PKC activation is an important early requirement for vestibular compensation during the acute post-labyrinthectomy period, while cyclic-nucleotide dependent kinases may be important in a later time frame.

Modulation by angiotensin II of isoproterenol-induced cAMP production in preglomerular microvascular smooth muscle cells from normotensive and genetically hypertensive rats

The objectives of the present study were to determine whether angiotensin II (Ang II) modifies beta-adrenoceptor-induced cAMP production in preglomerular microvascular smooth muscle cells (PMVSMCs), to determine whether the Ang II/beta-adrenoceptor interaction on cAMP production differs in PMVSMCs from normotensive Wistar-Kyoto (WKY) rats vs. PMVSMCs from spontaneously hypertensive rats (SHR), and to elucidate the mechanism of Ang II/beta-adrenoceptor interactions on cAMP production in PMVSMCs. In cultured PMVSMCs, isoproterenol increased cAMP levels and this effect was markedly enhanced by Ang II. The Ang II enhancement of isoproterenol-induced cAMP was significantly greater in SHR PMVSMCs compared with WKY PMVSMCs. Neither inhibition of calcineurin with FK506, inhibition of calcium-calmodulin with W-7 and calmidazolium, nor inhibition of Gi proteins with pertussis toxin attenuated Ang II enhancement of isoproterenol-induced cAMP in PMVSMCs from either SHR or WKY rats. Moreover, the effect of Ang II on isoproterenol-induced cAMP was not mimicked by alpha-2 adrenoceptor stimulation. In contrast, chelation of intracellular calcium with BAPTA-AM attenuated, increasing intracellular calcium with A23187 augmented, and inhibition of protein kinase C with either calphostin C or chelerythrine chloride abolished Ang II enhancement of isoproterenol-induced cAMP. We conclude that in cultured PMVSMCs Ang II enhances the cAMP response to beta-adrenoceptor agonists via a mechanism that involves coincident activation of adenylyl cyclase by stimulatory G proteins and protein kinase C. Thus, protein kinase C-mediated activation of adenylyl cyclase may attenuate Ang II-induced vasoconstriction in the renal microcirculation by raising the intracellular levels of cAMP, and this mechanism may be augmented in genetic hypertension.

A role of climbing fibers in regulation of flocculonodular lobe protein kinase C expression during vestibular compensation

The behavioral recovery from unilateral labyrinthectomy (UL) in rats is accompanied by asymmetric expression of Protein kinase C (PKC) in parasagittal regions of the flocculonodular lobe within 6 h after UL, which resolves to the control, symmetric pattern within 24 h. These changes consist of a regionally selective increase in the number of PKC-immunopositive Purkinje cells contralateral to the lesion. This study tested the hypotheses (1) that climbing fiber innervation inhibits PKC expression and (2) that climbing fibers are essential for the observed changes in PKC expression within 6 h after UL. The patterns of flocculonodular lobe Purkinje cell PKCdelta expression were analyzed 6 h post-operatively in both UL and sham-operated that had been treated previously with 3-acetylpyridine to destroy the inferior olive. These data were compared with previous results from rats with an intact olive. The results suggest that at least two signals regulate the zonal distribution of Purkinje cell PKCdelta expression in the flocculonodular lobe during the early period of compensation from UL. Climbing fiber activation appears to reduce PKC expression, while extraolivary mechanisms appear to up-regulate PKC expression. It is suggested that the climbing fiber signals may act as a molecular 'filter' or 'automatic gain control' which adjusts the contributions of these kinases to synaptic plasticity within the context of the background activity of climbing fibers.

Transient changes in flocculonodular lobe protein kinase C expression during vestibular compensation

Protein kinase C (PKC) is a family of intracellular signal transduction enzymes, comprising isoforms that vary in sensitivity to calcium, arachidonic acid, and diacylglycerol. PKC isoforms alpha, gamma, and delta are expressed by cerebellar Purkinje cells and neurons in the cerebellar nuclei and vestibular nuclei of the Long-Evans rat. In control rats, these PKCs are distributed symmetrically in the flocculonodular-lobe Purkinje cells. Behavioral recovery from vestibular dysfunction produced by unilateral labyrinthectomy (UL) is accompanied by asymmetric expression of PKC isoforms in these regions within 6 hr after UL. These expression changes were localized within parasagittal regions of the flocculus and nodulus. The distribution of PKCalpha, -gamma, and -delta were identical, suggesting that they are coregulated in cerebellar Purkinje cells during this early compensatory period. The pattern of Purkinje cell PKC expression returned to the control, symmetric distribution within 24 hr after UL. It is hypothesized that these regional changes in Purkinje cell PKC expression are an early intracellular signal contributing to vestibular compensation. In particular, regulation of PKC expression may contribute to changes in the efficacy of cerebellar synaptic plasticity during the acute post-UL period.

Lovastatin disrupts early events in insulin signaling: a potential mechanism of lovastatin's anti-mitogenic activity

The mechanism by which lovastatin lowers cholesterol levels is well characterized but little is known about its anti-mitogenic and anti-tumorigenic mechanism. Here we demonstrate that lovastatin disrupts early events in the mitogenic signaling pathways of insulin. Insulin treatment (200 mM) of quiescent HIR rat-1 fibroblasts results in an 8-fold stimulation of phosphatidylinositol-3-kinase (PI-3-K) activity. Overnight pretreatment of cells with lovastatin (20 microM) inhibits insulin stimulation of PI-3-K activity by 75%. Immunoprecipitation and immunoblotting experiments using antibodies against the regulatory subunit of PI-3-K (p85), phosphotyrosine, and insulin receptor alpha and beta subunits demonstrate that lovastatin inhibits the association of p85 with tyrosine phosphorylated insulin receptor substrate-1 and the beta subunit of the insulin receptor. Furthermore, lovastatin dramatically reduces (70-100%) the level of tyrosine phosphorylated insulin receptor beta subunit following insulin stimulation. These results clearly demonstrate that lovastatin disrupts early events of insulin mitogenic signaling by reducing the levels of tyrosine phosphorylated beta subunit and suggest that this disruption is a potential mechanism for the anti-mitogenic effect of lovastatin.

Characterization of Leishmania species from Peru

Twenty-six isolates of Leishmania parasites of Peruvian origin were studied by isoenzyme electrophoresis of four marker enzymes (ASAT, ALAT, G6PD and GPI), kinetoplast DNA hybridization and monoclonal antibody binding and compared with marker strains of the New World organisms L. b. braziliensis, L. b. guyanensis, L. m. mexicana and L. m. amazonensis. 12 of the isolates studied were of Andean origin; 11 of these were isolated from patients with Andean cutaneous leishmaniasis. The organisms originating from the Peruvian Amazonian forest were isolated from patients with cutaneous (12 cases) or mucocutaneous (2 cases) leishmaniasis. One of the Andean isolates was obtained from an infected phlebotomine vector. 25 of the new isolates were identified as L. braziliensis ssp. according to the three techniques employed. The results of monoclonal antibody binding showed that 23 of the isolates were indistinguishable from L. b. braziliensis. Two isolates identified as L. braziliensis ssp. according to their isoenzyme profiles and k-DNA hybridization patterns could not be classified at the subspecies level. The isolate obtained from the phlebotomine vector could not be identified. No evidence of the existence of parasites of the L. mexicana complex in Peruvian territory was found in this study. The results obtained show a remarkable similarity between Leishmania of Andean origin and L. b. braziliensis.