Retinal lesions induce fast intrinsic cortical plasticity in adult mouse visual system

Neuronal activity plays an important role in the development and structural–functional maintenance of the brain as well as in its life‐long plastic response to changes in sensory stimulation. We characterized the impact of unilateral 15° laser lesions in the temporal lower visual field of the retina, on visually driven neuronal activity in the afferent visual pathway of adult mice using in situ hybridization for the activity reporter gene zif268. In the first days post‐lesion, we detected a discrete zone of reduced zif268 expression in the contralateral hemisphere, spanning the border between the monocular segment of the primary visual cortex (V1) with extrastriate visual area V2M. We could not detect a clear lesion projection zone (LPZ) in areas lateral to V1 whereas medial to V2M, agranular and granular retrosplenial cortex showed decreased zif268 levels over their full extent. All affected areas displayed a return to normal zif268 levels, and this was faster in higher order visual areas than in V1. The lesion did, however, induce a permanent LPZ in the retinorecipient layers of the superior colliculus. We identified a retinotopy‐based intrinsic capacity of adult mouse visual cortex to recover from restricted vision loss, with recovery speed reflecting the areal cortical magnification factor. Our observations predict incomplete visual field representations for areas lateral to V1 vs. lack of retinotopic organization for areas medial to V2M. The validation of this mouse model paves the way for future interrogations of cortical region‐ and cell‐type‐specific contributions to functional recovery, up to microcircuit level.     

Dynamics of spatial frequency tuning in mouse visual cortex

Neuronal spatial frequency tuning in primary visual cortex (V1) substantially changes over time. In both primates and cats, a shift of the neuron's preferred spatial frequency has been observed from low frequencies early in the response to higher frequencies later in the response. In most cases, this shift is accompanied by a decreased tuning bandwidth. Recently, the mouse has gained attention as a suitable animal model to study the basic mechanisms of visual information processing, demonstrating similarities in basic neuronal response properties between rodents and highly visual mammals. Here we report the results of extracellular single-unit recordings in the anesthetized mouse where we analyzed the dynamics of spatial frequency tuning in V1 and the lateromedial area LM within the lateral extrastriate area V2L. We used a reverse-correlation technique to demonstrate that, as in monkeys and cats, the preferred spatial frequency of mouse V1 neurons shifted from low to higher frequencies later in the response. However, this was not correlated with a clear selectivity increase or enhanced suppression of responses to low spatial frequencies. These results suggest that the neuronal connections responsible for the temporal shift in spatial frequency tuning may considerably differ between mice and monkeys.     

Population structure of Glossina palpalis gambiensis (Diptera: Glossinidae) between river basins in Burkina Faso: Consequences for area-wide integrated pest management

African animal trypanosomosis is a major obstacle to the development of more efficient and sustainable livestock production systems in West Africa. Riverine tsetse species such as Glossina palpalis gambiensis Vanderplank are their major vectors. A wide variety of control tactics is available to manage these vectors, but their elimination will only be sustainable if control is exercised following area-wide integrated pest management (AW-IPM) principles, i.e. the control effort is targeting an entire tsetse population within a circumscribed area. In the present study, genetic variation at microsatellite DNA loci was used to examine the population structure of G. p. gambiensis inhabiting two adjacent river basins, i.e. the Comoé and the Mouhoun River basins in Burkina Faso. A remote sensing analysis revealed that the woodland savannah habitats between the river basins have remained unchanged during the last two decades. In addition, genetic variation was studied in two populations that were separated by a man-made lake originating from a dam built in 1991 on the Comoé. Low genetic differentiation was observed between the samples from the Mouhoun and the Comoé River basins and no differentiation was found between the samples separated by the dam. The data presented indicate that the overall genetic differentiation of G. p. gambiensis populations inhabiting two adjacent river basins in Burkina Faso is low (F_ST = 0.016). The results of this study suggest that either G. p. gambiensis populations from the Mouhoun are not isolated from those of the Comoé, or that the isolation is too recent to be detected. If elimination of the G. p. gambiensis population from the Mouhoun River basin is the selected control strategy, re-invasion from adjacent river basins may need to be prevented by establishing a buffer zone between the Mouhoun and the other river basin(s).     

The cross‐modal aspect of mouse visual cortex plasticity induced by monocular enucleation is age dependent

Monocular enucleation (ME) drastically affects the contralateral visual cortex, where plasticity phenomena drive specific adaptations to compensate for the unilateral loss of vision. In adult mice, complete reactivation of deprived visual cortex involves an early visually driven recovery followed by multimodal plasticity 3 to 7 weeks post ME (Van Brussel et al. [ 2011 ] Cereb. Cortex 21:2133–2146). Here, we specifically investigated the age dependence of the onset and the exact timing of both ME‐induced reactivation processes by comparing cortical activity patterns of mice enucleated at postnatal day (P) 45, 90, or 120. A swifter open‐eye potentiated reactivation characterized the binocular visual cortex of P45 mice. Nevertheless, even after 7 weeks, the reactivation remained incomplete, especially in the monocular cortex medial to V1. In comparison with P45, emergent cross‐modal participation was demonstrated in P90 animals, although robust reactivation similar to enucleated adults (P120) was not achieved yet. Concomitantly, at 7 weeks post ME, somatosensory and auditory cortex shifted from a hypoactive state in P45 to hyperactivity in P120. Thus, we provide evidence for a presensitive period in which gradual recruitment of cross‐modal recovery upon long‐term ME coincides with the transition from adolescence to adulthood in mice. J. Comp. Neurol. 522:950–970, 2014. © 2013 Wiley Periodicals, Inc.     

Long-term sampling of gamma sterilised male Glossina austeni (Diptera: Glossinidae) with sticky panels on Unguja Island (Zanzibar)

Daily catches of gamma sterilised male Glossina austeni Newstead with experimental sticky panels were analysed from March 1996 to July 1997. The flies were released weekly by light aircraft over primary and secondary forest ecosystems of Unguja Island, Zanzibar. In the primary forest, the cross-shaped royal blue XT panel (two interlocking panels of each 70 x 60 cm) trapped significantly more flies than the royal blue-white leg panel (panel with a body of 65 x 30 cm and two legs of each 15 x 15 cm) in all months, except in July 1996 and July 1997. In the same habitat, the cross-shaped royal blue-white leg panel (two interlocking leg panels) trapped from 1.7 (not significant) to 3.0 times (highly significant) as many flies as the standard leg panel depending on the season. Significantly more flies were trapped with the cross-shaped XT panel than with the leg panel in the secondary forest compared to the primary forest. Catches of the cross-shaped XT panel on each of a series of days, correlated well with those of the leg panel on the same day, except for panels deployed in the primary forest during the hot-dry and the beginning of the cold-dry season. Catches of the cross-shaped leg panel correlated less well with the catches of the standard leg panel in the primary forest. The data presented indicate that the behavioural responses in time and space of sterile male G. austeni are influenced by the type of trapping device used.     

Evaluation of the expression pattern of rAAV2/1, 2/5, 2/7, 2/8, and 2/9 serotypes with different promoters in the mouse visual cortex

This study compared the expression pattern, laminar distribution, and cell specificity of several rAAV serotypes (2/1, 2/5, 2/7, 2/8, and 2/9) injected in the primary visual cortex (V1) of adult C57Bl/6J mice. In order to obtain specific expression in certain neuron subtypes, different promoter sequences were evaluated for excitatory cell specificity: a universal cytomegalovirus (CMV) promoter, and two versions of the excitatory neuron‐specific Ca²⁺/calmodulin‐dependent kinase subunit α (CaMKIIα) promoter, CaMKIIα 0.4 and CaMKIIα 1.3. The spatial distribution as well as the cell type specificity was immunohistochemically verified. Depending on the rAAV serotype used, the transduced volume expressing reporter protein differed substantially (rAAV2/5 ? 2/7 ≈ 2/9 ≈ 2/8 ? 2/1). Excitatory neuron‐specific targeting was promoter‐dependent, with a surprising difference between the 1.3 kb and 0.4 kb CaMKIIα promoters. While CaMKIIα 1.3 and CMV carrying vectors were comparable, with 78% of the transduced neurons being excitatory for CMV and 82% for CaMKIIα 1.3, the shorter CaMKIIα 0.4 version resulted in 95% excitatory specificity. This study therefore puts forward the CaMKIIα 0.4 promoter as the best choice to target excitatory neurons with rAAVs. Together, these results can be used as an aid to select the most optimal vector system to deliver transgenes into specific rodent neocortical circuits, allowing further elucidation of their functions. J. Comp. Neurol. 523:2019–2042, 2015. © 2015 Wiley Periodicals, Inc.     

Mapping landscape friction to locate isolated tsetse populations that are candidates for elimination

Tsetse flies are the cyclical vectors of deadly human and animal trypanosomes in sub-Saharan Africa. Tsetse control is a key component for the integrated management of both plagues, but local eradication successes have been limited to less than 2% of the infested area. This is attributed to either resurgence of residual populations that were omitted from the eradication campaign or reinvasion from neighboring infested areas. Here we focused on Glossina palpalis gambiensis, a riverine tsetse species representing the main vector of trypanosomoses in West Africa. We mapped landscape resistance to tsetse genetic flow, hereafter referred to as friction, to identify natural barriers that isolate tsetse populations. For this purpose, we fitted a statistical model of the genetic distance between 37 tsetse populations sampled in the region, using a set of remotely sensed environmental data as predictors. The least-cost path between these populations was then estimated using the predicted friction map. The method enabled us to avoid the subjectivity inherent in the expert-based weighting of environmental parameters. Finally, we identified potentially isolated clusters of G. p. gambiensis habitat based on a species distribution model and ranked them according to their predicted genetic distance to the main tsetse population. The methodology presented here will inform the choice on the most appropriate intervention strategies to be implemented against tsetse flies in different parts of Africa. It can also be used to control other pests and to support conservation of endangered species.Tsetse flies transmit trypanosomes, the causative agents of sleeping sickness (human African trypanosomosis, HAT) and nagana (African animal trypanosomosis, AAT). Through increased disease surveillance and treatment, the number of HAT cases has substantially declined in the last 15 y (1). However, the elimination of HAT as a public health problem also requires effective vector management (1). AAT continues to represent the greatest animal-health constraint to improved livestock production in sub-Saharan Africa, causing enormous economic losses (e.g., milk and meat production) (2). AAT also constrains the integration of crop farming and livestock keeping, a crucial component for the development of sustainable agricultural systems (3). Indeed, AAT affects animal draft power, and consequently crop production. Also, keeping less productive trypanotolerant cattle breeds pushes farmers to increase herd sizes with such negative environmental impacts as overgrazing. As an example, in the Niayes area of Senegal, it was estimated that the eradication of tsetse flies would allow cattle sales to triple whereas herd sizes would decrease by 45% (4).     

Using species distribution models to optimize vector control in the framework of the tsetse eradication campaign in Senegal

Tsetse flies are vectors of human and animal trypanosomoses in sub-Saharan Africa and are the target of the Pan African Tsetse and Trypanosomiasis Eradication Campaign (PATTEC). Glossina palpalis gambiensis (Diptera: Glossinidae) is a riverine species that is still present as an isolated metapopulation in the Niayes area of Senegal. It is targeted by a national eradication campaign combining a population reduction phase based on insecticide-treated targets (ITTs) and cattle and an eradication phase based on the sterile insect technique. In this study, we used species distribution models to optimize control operations. We compared the probability of the presence of G. p. gambiensis and habitat suitability using a regularized logistic regression and Maxent, respectively. Both models performed well, with an area under the curve of 0.89 and 0.92, respectively. Only the Maxent model predicted an expert-based classification of landscapes correctly. Maxent predictions were therefore used throughout the eradication campaign in the Niayes to make control operations more efficient in terms of deployment of ITTs, release density of sterile males, and location of monitoring traps used to assess program progress. We discuss how the models’ results informed about the particular ecology of tsetse in the target area. Maxent predictions allowed optimizing efficiency and cost within our project, and might be useful for other tsetse control campaigns in the framework of the PATTEC and, more generally, other vector or insect pest control programs.Tsetse are vectors of human African trypanosomosis, a major neglected tropical disease (1), and African animal trypanosomosis (AAT), one of the most important pathological constraints to livestock development in 38 infested African countries (2). The Pan African Tsetse and Trypanosomiasis Eradication Campaign is a political initiative started in 2001 that calls for intensified efforts to reduce the tsetse and trypanosomosis problem (3). As part of this global effort, the government of Senegal embarked in 2007 on a tsetse eradication campaign in a 1,000-km² target area of the Niayes region, neighboring the capital Dakar. In this area, the limits of the distribution of the tsetse target populations were assessed using a stratified entomological sampling frame based on remote sensing indicators (4). The only tsetse species present was Glossina palpalis gambiensis Vanderplank, and it was responsible for the cyclical transmission of three trypanosome species, namely Trypanosoma vivax, T. congolense, and T. brucei brucei, listed in order of importance (5). The high prevalence of animal trypanosomosis in the Niayes (serological prevalence of 28.7% for T. vivax) hampered peri-urban intensification of cattle production (particularly dairy cattle). A population genetics study demonstrated that the G. p. gambiensis population of the Niayes was completely isolated from the main tsetse belt in the southeastern part of Senegal (6). This comprehensive set of entomological, veterinary, genetic, and other baseline data confirmed the isolated nature of the G. p. gambiensis population in the Niayes, which prompted the government of Senegal to select an eradication strategy using area-wide integrated pest management (AW-IPM) principles (7).The successful implementation of an AW-IPM strategy requires a thorough understanding of the ecology of the target population, particularly its spatial distribution, a study which was undertaken in the Niayes from 2007 to 2011 before the start of the operational eradication efforts. The selected strategy integrates insecticide-treated targets (ITTs) and cattle with the release of sterile insects. As the habitat of G. p. gambiensis is very fragmented (4), the targeting of suitable habitats for deployment of the ITTs is crucial to optimize cost efficiency (8) but also to enable the selection of appropriate sites for deployment of the monitoring traps to assess the impact of the control campaign. Although the initial entomological sampling was well-developed and efficiently implemented in the target area (4), we deem the development and use of population distribution models to be very beneficial in this regard.The use of species distribution models to optimize vector or pest control is quite novel. The existing tsetse distribution models (SI Text) were critical for a better understanding of tsetse distribution and AAT epidemiology, but their spatial resolution was not sufficient to guide an eradication process. In this paper, we used high-resolution images and recent advances in species distribution modeling methods to improve prediction accuracy. Predictive models, and more specifically machine-learning methods, were used to model the distribution of G. p. gambiensis (9). Model choice has an impact on the final output and also depends on the available data. In this study, both presence and absence data were available, which is uncommon with respect to tsetse data. Therefore, following Brotons et al., we used both datasets (10). Understanding how predictions from presence–absence models relate to predictions from presence-only models is important, because presence data are more reliable than absence data.Presence–absence data were modeled using a regularized logistic regression to avoid overfitting with respect to model parameters. There are various approaches to regularization for least square methods in statistical learning. The most widely used are the ridge regression and the lasso. Ridge regression bounds the regression coefficient space by adding the L2 norm (root square of the sum of squared values) of the coefficients to the residual sum of squares, whereas the lasso is a penalized least square method that shrinks the coefficient space by imposing an L1 penalty (sum of absolute values) on the regression coefficients. The elastic net framework used here is a compromise that combines ridge regression (L2 penalization) and the lasso (L1 penalization) for more flexibility in model selection (11). This model was chosen because of its flexibility and capacity to penalize complex models (12).A Maxent model was in addition used to model presence-only data (13). This model, which is one of the most widely used to model species distributions, is a machine-learning method based on maximum entropy. Absence data are replaced with so-called background data, which are a random sample of the available environment. Maxent fits a penalized maximum-likelihood model to avoid overfitting (L1 penalization). The logistic output from Maxent is a habitat suitability index rescaled to range from 0 to 1. Recently, the equivalence between Maxent and an infinitely weighted logistic regression was pointed out (14).The relationship between occurrence and environmental data was explored with multidimensional exploratory analysis. For this purpose, we used the ecological factor niche analysis (ENFA) (15), which is a presence-only multidimensional method based on the concept of ecological niche (16).The goal of this paper is to show how we selected among two competing approaches of species distribution modeling based on a large and accurate set of presence–absence data and how we used the results to optimize the eradication campaign in the Niayes of Senegal.     

Effects of irradiation,presence of females,and sugar supply on the longevity of sterile males Aedes albopictus (Skuse) under semi-field conditions on Reunion Island

Background

The development of the sterile insect technique (SIT) for reducing populations of Aedes albopictus (Skuse), (the vector of Chikungunya and Dengue fever), was studied in Reunion Island. For some mosquito species the sterilization process and mating activity may alter male survival. Most previous studies were carried out in the laboratory and may inadequately reflect the field situation. We conducted a semi-field experiment to evaluate the impact of sugar supply and mating activity under natural climatic conditions on wild and sterile male Ae. albopictus longevity, using large cages set up in an open clearing between trees and shrubs in Reunion Island.

Results

Wild males had a mean longevity of 15.5 days in the absence of females and with an immediate sugar supply; longevity in sterile males was similar. The presence of females greatly reduced both wild and especially sterile male lifespan; however, an immediate sugar supply could counteract this effect and allow sterile males to live an average of 11.6 days.

Conclusion

The outcomes indicate that sugar feeding could compensate for sterilization-induced damage, and that mating activity is not deleterious for well-fed males. This study stresses the critical importance of providing suitable sugar sources prior to release during SIT programmes.     

Universal primers for rapid detection of hytrosaviruses

Hytrosaviridae is a proposed virus family encompassing viruses that cause salivary gland hypertrophy (SGH) syndrome in infected insects and reduce the fertility in their dipteran insect hosts. They contain a large, double stranded DNA genome of 120-190 kbp. To date, these viruses have been detected only in adult Diptera. These include hytrosaviruses detected in various tsetse fly species (Glossina spp.), the narcissus bulb fly Merodon equestris and the house fly Musca domestica. The limited number of hytrosaviruses reported to date may be a reflection of the frequent absence of external symptoms in infected adult flies and the fact that the virus does not cause rapid mortality. Based on the complete genome sequence of Glossinia pallidipes (GpSGHV) and Musca domestica (MdSGHV) salivary gland hypertrophy viruses, a PCR based methodology was developed to detect the viruses in these species. To be able to detect hytrosaviruses in other Diptera, five degenerate primer pairs were designed and tested on GpSGHV and MdSGHV DNA using gradient PCR with annealing temperatures from 37 to 61 °C. Two pairs of primers were selected from p74, two pairs from PIF-1 and one pair from ODV-e66 homologous proteins. Four primer pairs generated a virus specific PCR product on both MdSGHV and GpSGHV at all tested annealing temperatures, while the ODV-e66 based primers did not generate a virus specific product with annealing temperatures higher that 47 °C. No non-specific PCR product was found when using genomic DNA of infected flies as template DNA. These results offer new sets of primers that could be used to detect hytrosaviruses in other insects.