Disruption of leptin receptor expression in the pancreas directly affects beta cell growth and function in mice

Obesity is characterized by hyperinsulinemia, hyperleptinemia, and an increase in islet volume. While the mechanisms that hasten the onset of diabetes in obese individuals are not known, it is possible that the adipose-derived hormone leptin plays a role. In addition to its central actions, leptin exerts biological effects by acting in peripheral tissues including the endocrine pancreas. To explore the impact of disrupting leptin signaling in the pancreas on beta cell growth and/or function, we created pancreas-specific leptin receptor (ObR) KOs using mice expressing Cre recombinase under the control of the pancreatic and duodenal homeobox 1 (Pdx1) promoter. The KOs exhibited improved glucose tolerance due to enhanced early-phase insulin secretion, and a greater beta cell mass secondary to increased beta cell size and enhanced expression and phosphorylation of p70S6K. Similar effects on p70S6K were observed in MIN6 beta cells with knockdown of the ObR gene, suggesting crosstalk between leptin and insulin signaling pathways. Surprisingly, challenging the KOs with a high-fat diet led to attenuated acute insulin secretory response to glucose, poor compensatory islet growth, and glucose intolerance. Together, these data provide direct genetic evidence, from a unique mouse model lacking ObRs only in the pancreas, for a critical role for leptin signaling in islet biology and suggest that altered leptin action in islets is one factor that contributes to obesity-associated diabetes.     

Characterization and ontogeny of synapse-associated proteins in the developing facial and hypoglossal motor nuclei of the Brazilian opossum

The characterization and ontogeny of synapse-associated proteins in the developing facial and hypoglossal motor nuclei were examined in the Brazilian opossum (Monodelphis domestica). Immunohistochemical markers utilized in this study were the synaptic vesicle-associated proteins synaptophysin and synaptotagmin; a synaptic membrane protein, plasma membrane-associated protein of 25 kDa (SNAP-25); a growth cone protein, growth-associated phosphoprotein-43 (GAP-43); and the microtubule-associated proteins axonal marker τ and dendritic marker microtubule-associated protein-2 (MAP-2). In this study, we have found that during the first 10 postnatal days (1–10 PN), the facial motor nucleus lacked immunoreactivity for synaptophysin, synaptotagmin, GAP-43, τ, and SNAP-25. After 10 PN, immunoreactivity increased in the facial motor nucleus for synaptophysin, synaptotagmin, GAP-43, and τ, whereas immunoreactivity for SNAP-25 was not evident until between 15 and 25 PN. Conversely, immunoreactivity for MAP-2, was present in the facial motor nucleus from the day of birth. In contrast, the hypoglossal motor nucleus displayed immunoreactivity from 1 PN for synaptophysin, synaptotagmin, SNAP-25, GAP-43, τ, and MAP-2. These results suggest that the facial motor nucleus of the opossum may not receive afferent innervation as defined by classical synaptic markers until 15 PN and, further, that characteristic mature synapses are not present until between 15 and 25 PN. These results indicate that there may be a delay in synaptogenesis in the facial motor nucleus compared to synaptogenetic events in the hypoglossal motor nucleus. Because the facial motor nucleus is active prior to completion of synaptogenesis, we suggest that the facial motoneurons are regulated in a novel or distinct manner during this time period. © 1996 Wiley-Liss, Inc.     

Expression of various multidrug resistance-associated protein (MRP) homologues in brain microvessel endothelial cells

Multidrug resistance-associated protein (MRP) actively transports a broad range of anionic compounds out of the cell. To date, six different homologues of MRP (i.e. MRP1-MRP6) have been identified. The current study examines the expression of the various MRP homologues in both primary cultured bovine brain microvessel endothelial cells (BBMEC) and the capillary-enriched fraction from bovine brain homogenates. RT-PCR analysis demonstrated the presence of MRP1, MRP4, MRP5 and MRP6 in both BBMEC and the capillary-enriched fractions of brain homogenates. While low levels of MRP3 were detected in the BBMEC, it was not observed in the capillary-enriched fraction. In addition, RT-PCR and Western blot studies indicated an absence of MRP2 expression in both blood-brain barrier preparations. The presence of several different MRP homologues in the brain microvessel endothelial cells may be important in controlling the permeability of the blood-brain barrier to organic anions.     

Determination of optimal cryoprotectants and procedures for their addition and removal from human spermatozoa

The objective was to test the hypothesis that the optimal cryoprotective agent for cryopreservation of human spermatozoa would be a solute for which cells have the highest plasma membrane permeability, resulting in the least amount of volume excursion during its addition and removal. To test this hypothesis, theoretical simulations were performed using membrane permeability coefficients to predict optimal procedures for the addition and removal of a cryoprotectant. Simulations were performed using data from four different cryoprotectants: (i) glycerol, (ii) dimethyl sulphoxide, (iii) propylene glycol and (iv) ethylene glycol. Thermodynamic formulations were applied to determine approaches for the addition and removal of 1 M and 2 M final concentrations of cryoprotectant, allowing the spermatozoa to maintain a cell volume within their osmotic tolerance limits. Based on these data, ethylene glycol was predicted to be optimal for minimizing volume excursions among the solutes evaluated. These predictions were then experimentally tested using glycerol as the control cryoprotectant and ethylene glycol as the experimental cryoprotectant. The results indicate that there was a higher (P < 0.05) recovery of motile spermatozoa after cryopreservation when using 1 M ethylene glycol than with 1 M glycerol, supporting the hypothesis that use of the cryoprotectant for which the cell has the highest permeability will result in higher cell survival.      

Donor insemination: Dutch parents' opinions about confidentiality and donor anonymity and the emotional adjustment of their children

Results from a comparative study investigating 38 donor insemination (DI) Dutch families with 4-8 year old children are presented. The aims of this study were to investigate parents' opinions on the issues of confidentiality and donor anonymity, to assess the emotional development of the children, and to examine in DI families the association between secrecy with regard to the use of a donor and the emotional adjustment of the children. The DI families were compared to families with a child conceived by in-vitro fertilization (IVF) and to families with a naturally conceived child. Secrecy appeared to be associated with DI and not with IVF: 74% of the DI parents intended not to inform the child about the way in which she/he was conceived, whereas none of the IVF parents intended to keep the secret. Only one set of DI parents and two sets of IVF parents had actually told the child. As to donor anonymity, a spread of opinions appeared among DI parents; 57% preferred an anonymous donor, 31% would have liked non- identifying information about the donor, 9% preferred the donor's identity to be registered and 3% remained unsure. Parents' major concern was to know more about the medical/genetic background of the donor. Mothers and fathers in the DI families differed in their opinions concerning the issues of confidentiality and donor anonymity: fathers, more often than mothers, were secretive with regard to the use of a donor and husbands, more often than their wives, were in favour of donor anonymity. With regard to the emotional development of the children, more emotional/behavioural problems were revealed among DI children than among children who were naturally conceived. No association was found between secrecy and the emotional/behavioural adjustment of the children.      

Effect of vitamin A adjunct therapy for cerebral malaria in children admitted to Mulago hospital: a randomized controlled trial

Background

Malaria is a leading cause of mortality in Uganda accounting for 25% of deaths among children. Hitherto no adjunct therapy has been identified to improve outcome of cerebral malaria. Retinol suppresses growth of P.falciparum, scavenges free radicals, and exhibits synergistic action with quinine in parasite clearance.

Objective

To determine the effect of vitamin A supplementation on treatment outcome of cerebral malaria

Methods

In this randomised double-blind placebo controlled clinical trial we studied 142 children aged 6–59 months admitted with cerebral malaria in Mulago Hospital, Kampala. Children were randomised to either vitamin A or placebo and followed for 7 days. The main outcome measures were coma recovery time, time for convulsions to stop, and parasite and fever clearance. Secondary outcomes were overall mortality and time taken to start oral feeds.

Results

There was no difference in the coma recovery time (p=0.44), resolution of convulsions (p=0.37), fever clearance (p=0.92), parasite clearance (p=0.12), and starting oral feeds between the two treatment groups. Mortality was higher (16.2%) in the placebo than in the vitamin A group (8.1%): RR 1.4; 95% CI 1.0–2.1.

Conclusions

Vitamin A as adjunct therapy did not significantly reduce coma duration but there were fewer deaths in the vitamin A arm.     

High-fat feeding promotes obesity via insulin receptor/PI3K-dependent inhibition of SF-1 VMH neurons

Steroidogenic factor 1 (SF-1)-expressing neurons of the ventromedial hypothalamus (VMH) control energy homeostasis, but the role of insulin action in these cells remains undefined. We show that insulin activates phosphatidylinositol-3-OH kinase (PI3K) signaling in SF-1 neurons and reduces firing frequency in these cells through activation of K(ATP) channels. These effects were abrogated in mice with insulin receptor deficiency restricted to SF-1 neurons (SF-1(ΔIR) mice). Whereas body weight and glucose homeostasis remained the same in SF-1(ΔIR) mice as in controls under a normal chow diet, they were protected from diet-induced leptin resistance, weight gain, adiposity and impaired glucose tolerance. High-fat feeding activated PI3K signaling in SF-1 neurons of control mice, and this response was attenuated in the VMH of SF-1(ΔIR) mice. Mimicking diet-induced overactivation of PI3K signaling by disruption of the phosphatidylinositol-3,4,5-trisphosphate phosphatase PTEN led to increased body weight and hyperphagia under a normal chow diet. Collectively, our experiments reveal that high-fat diet-induced, insulin-dependent PI3K activation in VMH neurons contributes to obesity development.