Astrocyte GluN2C NMDA receptors control basal synaptic strengths of hippocampal CA1 pyramidal neurons in the stratum radiatum

Experience-dependent plasticity is a key feature of brain synapses for which neuronal N-Methyl-D-Aspartate receptors (NMDARs) play a major role, from developmental circuit refinement to learning and memory. Astrocytes also express NMDARs, although their exact function has remained controversial. Here, we identify in mouse hippocampus, a circuit function for GluN2C NMDAR, a subtype highly expressed in astrocytes, in layer-specific tuning of synaptic strengths in CA1 pyramidal neurons. Interfering with astrocyte NMDAR or GluN2C NMDAR activity reduces the range of presynaptic strength distribution specifically in the stratum radiatum inputs without an appreciable change in the mean presynaptic strength. Mathematical modeling shows that narrowing of the width of presynaptic release probability distribution compromises the expression of long-term synaptic plasticity. Our findings suggest a novel feedback signaling system that uses astrocyte GluN2C NMDARs to adjust basal synaptic weight distribution of Schaffer collateral inputs, which in turn impacts computations performed by the CA1 pyramidal neuron.

Field Ecology and Food Suitability of Tarsonemus spp. (Acari: Tarsonemidae)

Tarsonemus bakeri Ewing (Acari: Tarsonemidae) is a species of mite commonly associated with citrus in many countries including the United States. A short report in 1942 suggested this species is phytophagous, but it has not been reported as a pest in citrus or any other crop since then. A single survey of 78 orchards in three growing regions in California demonstrated that Tarsonemus spp. mites were only associated with leaf samples that had visible sooty mold. A seasonal population study in one citrus orchard showed that all life stages of Tarsonemus spp. were present year-round on leaves and fruit, with the population on fruit reaching a peak in December (59.7 ± 15.2 mites per fruit). Results from a food suitability study showed that the population declined sharply on both plastic and leaf substrate when the mites were not provided a supplementary food source. When supplementary food was provided in the form of Alternaria, honeydew, molasses, or combinations of these, mites survived and multiplied throughout the 29-d study, irrespective of the substrate. Tarsonemus bakeri were found on excised, decaying leaves collected from an orchard. These studies verify that Tarsonemus spp. are associated only with sooty mold in citrus orchards. T. bakeri populations cannot sustain themselves on leaf tissue alone, indicating that they are nondamaging to citrus and therefore need not be considered a phytosanitary concern by importing countries.

Food Suitability and Population Dynamics of Lorryia formosa (Acari: Tydeidae)

Lorryia formosa Cooreman (Acari: Tydeidae) is a species of mite commonly associated with citrus in many countries including the United States. A survey report in 1957 suggested phytophagous nature, while other studies claimed that L. formosa populations are associated with honeydew producing insects and sooty mold and it acts as a sanitizing agent. We investigated the effect of various diets on the survival and progeny production of L. formosa on excised leaves and the survival and potential to cause feeding damage to leaves of potted plants in a greenhouse study. A 2-yr field survey of a mandarin orchard was also conducted to elucidate the seasonal infestation, damage potential and population structure of L. formosa in a natural habitat. Results showed that all L. formosa adults and immatures died in less than 14 d on excised leaves, did not survive beyond 7 d on potted citrus plants alone, and caused no observable feeding damage to leaves or fruit. When sugar water, honeydew, or cottony cushion scale, Icerya purchasi Maskell (Hemiptera: Margarodidae), was present, adults and immatures survived the duration of the experiments and produced additional generations. The field survey showed that all stages of L. formosa were present in a mandarin orchard throughout the year and insecticide applications affected but did not eliminate mite populations. Fruit generally had a greater percentage infestation of mites (44.8 ± 4.0) than leaves (16.0 ± 4.7). These studies confirmed that L. formosa cannot sustain a population on leaf tissue alone and is nondamaging to citrus in California.

DNA-based mutation assay GPMA (genome profiling-based mutation assay): reproducibility, parts-per-billion scale sensitivity, and introduction of a mammalian-cell-based approach

Genome profiling-based mutation assay (GPMA) is, to date, the only DNA sequence-based mutation assay that directly measures DNA alterations induced by mutagens. Here, the all-important congruence of mutagen assignment between DNA-based GPMA and the phenotype-based Ames test (the gold standard of mutagen assays) was confirmed qualitatively and semi-quantitatively by means of 94 chemical species (including previously examined 64). The high sensitivity (on the order of 10 ppb) and reproducibility of GPMA were also corroborated by the match between virtually independent experiments conducted in the distant past (10 years ago) and recently. Meanwhile, a standard experimental framework was established: the conditions of 100 parts per billion (ppb) concentration of a chemical and 15-generation culture of Escherichia coli. Moreover, a mammalian cell line (NIH 3T3) was shown to be suitable as a tester organism for the GPMA approach. Preliminary experimental results suggested that this approach can provide a qualitatively equivalent and quantitatively different mutagen assay results relative to the bacteria-based GPMA (renamed as bGPMA). This finding confirmed the effectiveness of the GPMA approach and indicates that mGPMA is a promising way to detect mammalian-cell mutagens.

Phosphine Resistance in Adult and Immature Life Stages of Tribolium castaneum (Coleoptera: Tenebrionidae) and Plodia interpunctella (Lepidoptera: Pyralidae) Populations in California

Phosphine resistance in stored-product insects occurs worldwide and is a major challenge to continued effective use of this fumigant. We determined resistance frequencies and levels of resistance in Tribolium castaneum and Plodia interpunctella collected from California almond storage and processing facilities. Discriminating doses of phosphine were established for eggs and larvae of P. interpunctella and eggs of T. castaneum using laboratory susceptible strains of the two species. For T. castaneum and P. interpunctella eggs, discriminating doses were 62.4 and 107.8 ppm, respectively, over a 3-d fumigation period, and for P. interpunctella larvae, discriminating dose was 98.7 ppm over a 20-h fumigation period. Discriminating dose tests on adults and eggs showed that 4 out of 11 T. castaneum populations tested had resistance frequencies that ranged from 42 to 100% for adults and 54 to 100% for eggs. LC99 values for the susceptible and the most resistant adults of T. castaneum were 7.4 and 356.9 ppm over 3 d, respectively. LC99 values for T. castaneum eggs were 51.5 and 653.9 ppm, respectively. Based on adult data, the most resistant T. castaneum beetle population was 49× more resistant than the susceptible strain. Phosphine resistance frequencies in P. interpunctella eggs ranged from 4 to 20%. Results show phosphine resistance is present in both species in California. Future research will investigate phosphine resistance over a wider geographic area. In addition, the history of pest management practices in facilities where insects tested in this study originated will be determined in order to develop phosphine resistance management strategies for California almond storage and processing facilities.

Contact Toxicity of Deltamethrin Against Tribolium castaneum (Coleoptera: Tenebrionidae), Sitophilus oryzae (Coleoptera: Curculionidae), and Rhyzopertha dominica (Coleoptera: Bostrichidae) Adults

This study was conducted at Oklahoma State University, Stillwater, OK, to evaluate the response to deltamethrin concentrations for adults of three stored-product insects, Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Rhyzopertha dominica (F.). In insect toxicological studies, knockdown is the state of intoxication and partial paralysis as a result of exposure to an insecticide. Deltamethrin concentrations ranging from 0.48 to 140 mg/m(2) (1 to 3,000 ppm) were sprayed on glass Petri dishes. After the dishes dried, 20 adult insects of each species were placed on the treated dishes to determine the contact toxicity of deltamethrin. Assessments for knockdown were made at 15-min intervals for up to 8 h after initial exposure and then again after 24 or 48 h. Insects were then transferred to clean untreated Petri dishes with diet and observed from 0.5 to 72 h. Mortality was assessed 72 h after transfer to untreated dishes with food material. Deltamethrin was highly effective against all three species tested and achieved 99% knockdown of insects of all species within 4 h after exposure at concentrations ≥1.2 mg/m(2) Although some insects recovered from initial knockdown at concentrations ≤48 mg/m(2), nearly all the insects were killed at 140 mg/m(2) when exposed for 48 h. LC95 values for all species tested, for the 48-h exposure period, were <140 mg/m(2), the concentration of deltamethrin that could potentially be present in new ZeroFly Storage Bag fabric. ZeroFly bags are used for stored-product insect pest control.

Population Growth and Development of the Psocid Liposcelis fusciceps (Psocoptera: Liposcelididae) at Constant Temperatures and Relative Humidities

We investigated the effects of seven temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, and 37.5°C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis fusciceps Badonnel (Psocoptera: Liposcelididae). Results demonstrated that L. fusciceps did not survive at 43% RH, at all temperatures tested. At 55% RH, L. fusciceps did not survive at the highest three temperatures and no psocids survived at 37.5°C and 63% RH. The highest population growth was recorded at 30.0°C and 75% RH where populations increased 16-fold from an initial population of five females. L. fusciceps males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 28, 70, and 2%, respectively. Female L. fusciceps have two to five instars, and the percentages of females with two, three, four, and five instars were 2, 33, 63, and 2%, respectively. The total developmental time for males was shorter than females. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. Based on 30-d population growth, L. fusciceps can survive and multiply at a relative humidity of 55% at 22.5-30.0°C, but does better at 27.5-32.5°C and a higher relative humidity of 75%. Relative humidities of ≤ 63% and temperatures of ≥ 32.5°C are detrimental to L. fusciceps. These data provide a better understanding of L. fusciceps population dynamics and can be used to develop effective management strategies for this psocid.

Weight loss and germination failure caused by psocids in different wheat varieties

We investigated weight loss caused by Liposcelis entomophila (Enderlein) feeding in damaged (cracked) and intact kernels of 'Jagger' variety of hard red winter wheat over a 90-d period at 30 +/- 1 degrees C and 75 +/- 5% relative humidity. L. entomophila caused 8.5% weight loss in damaged wheat kernels, which was significantly greater than the weight loss found in intact wheat kernels (0.2%). We also evaluated the suitability of six wheat varieties commonly grown in Oklahoma, namely, Jagger, 'Endurance,' 'Overley,' 'Jagalene,' 'OK Bullet,' and 'Deliver' to support populations of four psocid species, namely, Liposcelis bostrychophila Badonnel, L. decolor (Pearman), L. entomophila, and L. paeta Pearman over a 30-d period. The greatest population increase was observed in L. bostrychophila followed by L. paeta. Subsequently, weight loss of damaged and intact wheat kernels and germination of intact kernels infested by L. paeta over a 45-d period were assessed in OK Bullet variety. L. paeta caused weight loss of 3.3% in damaged kernels, which was significantly greater than the weight loss found in intact kernels (0.4%). Based on our data, 40% of infested intact kernels failed to germinate after 45 d of infestation by L. paeta, but this decreased to 32% when adjusted using germination failure of uninfested kernels. Our data show that psocid infestations do not only cause considerable loss in weight of wheat, but also result in significant germination failure. These data call for the formulation of effective integrated psocid management strategies for stored wheat to mitigate the negative impacts of psocid pests.

Population growth and development of Liposcelis pearmani (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

Psocids of genus Liposcelis are now considered serious pests of stored products. We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0°C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis pearmani Lienhard. L. pearmani did not survive at 37.5 and 40.0°C, at all relative humidities tested; at 43% RH, at all temperatures tested; and at 55% RH, at 32.5 and 35°C. The greatest population growth was recorded at 32.5°C and 75% RH (32-fold growth). L. pearmani males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 17, 63, and 20%, respectively. Female L. pearmani have two to five instars, and the percentages of females with two, three, four, and five instars were 5, 39, 55, and 1%, respectively. We developed temperature-dependent development equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. Based on 30-d population growth, L. pearmani cannot survive at temperatures >35.0°C; does not thrive at low relative humidities (55%), at temperatures above 25°C; and has a high optimum relative humidity for population growth (75%). Therefore, we expect it to have a more limited distribution compared with other Liposcelis species. These data provide a better understanding of how temperature and RH may influence L. pearmani population dynamics and can be used in population growth models to help develop effective management strategies for this psocid, and to predict its occurrence.

Population growth and development of the psocid Liposcelis rufa (Psocoptera: Liposcelididae) at constant temperatures and relative humidities

We investigated the effects of eight temperatures (22.5, 25.0, 27.5, 30.0, 32.5, 35.0, 37.5, and 40.0 degrees C) and four relative humidities (43, 55, 63, and 75%) on population growth and development of the psocid Liposcelis rufa Broadhead (Psocoptera: Liposcelididae). L. rufa did not survive at 43% RH, at all temperatures tested; at 55% RH, at the highest four temperatures; and at 63% RH and 40.0 degrees C. The greatest population growth was recorded at 35.0 degrees C and 75% RH (73-fold growth). At 40.0 degrees C, L. rufa populations declined or barely grew. L. rufa males have two to four nymphal instars, and the percentages of males with two, three, and four instars were 31, 54, and 15%, respectively. Female L. rufa have two to five instars, and the percentages of females with two, three, four, and five instars were 2, 44, 42, and 12%, respectively. The life cycle was shorter for males than females. We developed temperature-dependent developmental equations for male and female eggs, individual nymphal, combined nymphal, and combined immature stages. The ability of L. rufa to reproduce at a relative humidity of 55% and temperatures of 22.5-30.0 degrees C and at relative humidities of 63-75% and temperatures of 22.5-37.5 degrees C, in addition to being able to survive at 40.0 degrees C, suggests that this species would be expected to have a broader distribution than other Liposcelis species. These data provide a better understanding of L. rufa population dynamics and can be used to help develop effective management strategies for this psocid.

Exploration of fluorescent protein voltage probes based on circularly permuted fluorescent proteins

Genetically encoded fluorescent protein (FP) voltage sensors are promising tools for optical monitoring of the electrical activity of cells. Over the last decade, several designs of fusion proteins have been explored and some of them have proven to be sensitive enough to record membrane voltage transients from single mammalian cells. Most prominent are the families of voltage sensitive fluorescent proteins (VSFPs) that utilize the voltage sensor domain (VSD) of Ciona intestinalis voltage sensor-containing phosphatase (Ci-VSP). The voltage sensitivity of the fluorescence readout of these previously reported membrane potential indicators is achieved either via a change in the efficiency of fluorescence resonance energy transfer between two FP spectral variants or via modulation in the fluorescence intensity of a single FP. Here, we report our exploration on a third VSFP design principle based on circularly permuted fluorescent protein (cpFP) variants. Using circularly permuted EGFP derived from GCaMP2 and two newly generated circularly permuted variants of the far-red emitting protein named mKate, we generated and characterized a series of voltage-sensitive probes wherein the cpFPs were fused to the VSD of Ci-VSP. The most promising variants were based on circularly permuted mKate with new N- and C-termini given by residues 180 and 182. Even so their voltage sensitivity was relatively modest, they constitute a proof of principle for this novel protein design.

Second and third generation voltage-sensitive fluorescent proteins for monitoring membrane potential

Over the last decade, optical neuroimaging methods have been enriched by engineered biosensors derived from fluorescent protein (FP) reporters fused to protein detectors that convert physiological signals into changes of intrinsic FP fluorescence. These FP-based indicators are genetically encoded, and hence targetable to specific cell populations within networks of heterologous cell types. Among this class of biosensors, the development of optical probes for membrane potential is both highly desirable and challenging. A suitable FP voltage sensor would indeed be a valuable tool for monitoring the activity of thousands of individual neurons simultaneously in a non-invasive manner. Previous prototypic genetically-encoded FP voltage indicators achieved a proof of principle but also highlighted several difficulties such as poor cell surface targeting and slow kinetics. Recently, we developed a new series of FRET-based Voltage-Sensitive Fluorescent Proteins (VSFPs), referred to as VSFP2s, with efficient targeting to the plasma membrane and high responsiveness to membrane potential signaling in excitable cells. In addition to these FRET-based voltage sensors, we also generated a third series of probes consisting of single FPs with response kinetics suitable for the optical imaging of fast neuronal signals. These newly available genetically-encoded reporters for membrane potential will be instrumental for future experimental approaches directed toward the understanding of neuronal network dynamics and information processing in the brain. Here, we review the development and current status of these novel fluorescent probes.