IRS-2 Deficiency Impairs NMDA Receptor-Dependent Long-term Potentiation

The beneficial effects of insulin and insulin-like growth factor I on cognition have been documented in humans and animal models. Conversely, obesity, hyperinsulinemia, and diabetes increase the risk for neurodegenerative disorders including Alzheimer's disease (AD). However, the mechanisms by which insulin regulates synaptic plasticity are not well understood. Here, we report that complete disruption of insulin receptor substrate 2 (Irs2) in mice impairs long-term potentiation (LTP) of synaptic transmission in the hippocampus. Basal synaptic transmission and paired-pulse facilitation were similar between the 2 groups of mice. Induction of LTP by high-frequency conditioning tetanus did not activate postsynaptic N-methyl-D-aspartate (NMDA) receptors in hippocampus slices from Irs2−/− mice, although the expression of NR2A, NR2B, and PSD95 was equivalent to wild-type controls. Activation of Fyn, AKT, and MAPK in response to tetanus stimulation was defective in Irs2−/− mice. Interestingly, IRS2 was phosphorylated during induction of LTP in control mice, revealing a potential new component of the signaling machinery which modulates synaptic plasticity. Given that IRS2 expression is diminished in Type 2 diabetics as well as in AD patients, these data may reveal an explanation for the prevalence of cognitive decline in humans with metabolic disorders by providing a mechanistic link between insulin resistance and impaired synaptic transmission

Biocontrol Potential of Forest Tree Endophytes

Peer reviewe

Effect of Metalaxyl Plus PCNB or Metalaxyl Plus Tolclofos-methyl on Peanut Pod Rot and Soil Populations of <i>Pythium</i> spp. and <i>Rhizoctonia solani</i>

Abstract Metalaxyl plus PCNB or metalaxyl plus tolclofos-methyl were field tested in 1985–1987 in Oklahoma for their effect on pod rot of Florunner and Spanco peanut caused by Pythium spp. and Rhizoctonia solani. Total a.i. (kg/ha) of metalaxyl and PCNB applied in 1985, 1986 and 1987 were 1.12 and 11.2, 1.12 and 11.2 and 0.92 and 7.40. respectively. Total a.i. (kg/ha) of metalaxyl plus tolclofos-methyl applied in 1986 and 1987 were 1.34 and 3.36 and 1.12 and 2.24, respectively. Fungicides reduced pod rot severity on both cultivars at 2–8 wks prior to harvest; at harvest, however, none of the reductions were significant (P≤0.05). Yield increases were measured from 111–579 kg/ha, but few increases were significant (P≤0.05). Fungicides generally reduced the number of Pythium propagules in soil at several sampling dates, but few of the reductions were significant (P≤0.05). In 1986 and 1987 populations of Pythium spp. in soil peaked at 60 and 75 days, respectively, then declined. At these peaks treated soils generally had fewer Pythium propagules than nontreated soils. Populations of Pythium spp. were not significantly reduced at harvest. Populations of R. solani were highly variable over the seasons and control was erratic from year to year. In combination with metalaxyl, tolclofos-methyl was no more effective than PCNB in reducing pod rot or populations of R. solani. Populations of R. solani at harvest were not significantly (P≤0.05) reduced by the fungicide combinations.</jats:p

Reaction of Peanut Cultivars to Pythium Pod Rot and Their Influence on Populations of <i>Pythium</i> spp. in Soil1

Abstract In four field experiments the peanut cultivars Florigiant and NC 7 were generally more susceptible (P = 0.05) than Pronto and Spanco to pod rot and sometimes more susceptible (P = 0.05) than Florunner, GK 7, Langley or Okrun. The pod rot susceptibility of Florunner, GK 7, Langley, Okrun, Pronto and Spanco was usually similar. No consistent cultivar differences (P = 0.05) among pod yields were observed. Pythium myriotylum was the dominant species isolated from infected hull pieces plated on a medium selective for pythiaceous fungi. No cultivar significantly reduced populations of Pythium spp. in the soils of their pegging zones. In 1987, populations of Pythium spp. in soils at Ft. Cobb and Madill, Oklahoma increased at 67 days after planting (DAP) but declined at 89 DAP. in 1988 a similar population trend occurred at Ft. Cobb at 89 DAP and at Enos, Oklahoma at 127 DAP. The increase and decline of Pythium spp. were probably not directly influenced by soil temperature or matric potential. The involvement of the peanut plant in the fluctuation of Pythium spp. in soil is a plausible explanation for this trend.</jats:p

Bacterial chemotaxis to fungal propagules <i>in vitro</i> and in soil

Erwinia herbicola, Pseudomonas fluorescens, and P. putida were strongly attracted in vitro to substances exuded by conidia of Cochliobolus victoriae and sclerotia of Macrophomina phaseolina, but not to phosphate buffer solution. Numbers of bacteria attracted to propagules of C. victoriae or M. phaseolina in an unsterilized sandy loam soil were significantly (P = 0.05) greater than background populations occurring in soil saturated with buffer. Chemotactic response was greater to C. victoriae than to M. phaseolina both in vitro and in soil. Results suggest that living fungal propagules may act as attractants for motile bacteria in soil. </jats:p

Exudation from ¹⁴C-labeled fungal propagules in the presence of specific microorganisms

Exudation from 14C-labeled conidia of Cochliobolus victoriae and sclerotia of Macrophomina phaseolina was greater in the presence of cells of five bacterial species or propagules of four fungal species in phosphate buffer or in sterilized soil than in buffer without other microorganisms. In most instances, the increased exudation was statistically significant at P = 0.05. High population densities of bacterial cells or fungal propagules induced greater exudation than lower densities. 14C exudation from C. victoriae conidia in the presence of specific microorganisms was 1.5–9.9% of total label in buffer and 1.0–3.8% on soil; exudation from M. phaseolina sclerotia was 1.4–3.2% of total label in buffer and 1.3–3.2% on soil. All microorganisms tested, except Actinoplanes utahensis and M. phaseolina, suppressed germination of conidia of C. victoriae and sclerotia of M. phaseolina in vitro. Exudation of 14C-labeled compounds was inversely correlated with germination of C. victoriae conidia (r = −0.72) and M. phaseolina sclerotia (r = −0.74). The results indicate that specific microorganisms can enhance exudation from fungal propagules and that the enhanced exudation may be related to the imposition of mycostasis. </jats:p