A computational model of stereoscopic prey capture in praying mantises

We present a simple model which can account for the stereoscopic sensitivity of praying mantis predatory strikes. The model consists of a single “disparity sensor”: a binocular neuron sensitive to stereoscopic disparity and thus to distance from the animal. The model is based closely on the known behavioural and neurophysiological properties of mantis stereopsis. The monocular inputs to the neuron reflect temporal change and are insensitive to contrast sign, making the sensor insensitive to interocular correlation. The monocular receptive fields have a excitatory centre and inhibitory surround, making them tuned to size. The disparity sensor combines inputs from the two eyes linearly, applies a threshold and then an exponent output nonlinearity. The activity of the sensor represents the model mantis’s instantaneous probability of striking. We integrate this over the stimulus duration to obtain the expected number of strikes in response to moving targets with different stereoscopic disparity, size and vertical disparity. We optimised the parameters of the model so as to bring its predictions into agreement with our empirical data on mean strike rate as a function of stimulus size and disparity. The model proves capable of reproducing the relatively broad tuning to size and narrow tuning to stereoscopic disparity seen in mantis striking behaviour. Although the model has only a single centre-surround receptive field in each eye, it displays qualitatively the same interaction between size and disparity as we observed in real mantids: the preferred size increases as simulated prey distance increases beyond the preferred distance. We show that this occurs because of a stereoscopic “false match” between the leading edge of the stimulus in one eye and its trailing edge in the other; further work will be required to find whether such false matches occur in real mantises. Importantly, the model also displays realistic responses to stimuli with vertical disparity and to pairs of identical stimuli offering a “ghost match”, despite not being fitted to these data. This is the first image-computable model of insect stereopsis, and reproduces key features of both neurophysiology and striking behaviour.     

Maternal Infection Is a Risk Factor for Early Childhood Infection in Filariasis

Background

Global Program to Eliminate Lymphatic Filariasis (GPELF) launched by WHO aims to eliminate the disease by 2020. To achieve the goal annual mass drug administration (MDA) with diethylcarbamazine (DEC) plus albendazole (ABZ) has been introduced in all endemic countries. The current policy however excludes pregnant mothers and children below two years of age from MDA. Since pregnancy and early childhood are critical periods in determining the disease outcome in older age, the present study was undertaken to find out the influence of maternal filarial infection at the time of pregnancy on the susceptibility outcome of children born in a community after implementation of MDA for the first time.

Methodology and Principal Findings

The participants in this cohort consists of pregnant mothers and their subsequently born children living in eight adjacent villages endemic for filarial infections, in Khurda District, Odisha, India, where MDA has reduced microfilariae (Mf) rate from 12% to 0.34%. Infection status of mother and their children were assessed by detection of Mf as well as circulating filarial antigen (CFA) assay. The present study reveals a high rate of acquiring filarial infection by the children born to infected mother than uninfected mothers even though Mf rate has come down to < 1% after implementation of ten rounds of MDA.

Significance

To attain the target of eliminating lymphatic filariasis the current MDA programme should give emphasis on covering the women of child bearing age. Our study recommends incorporating supervised MDA to Adolescent Reproductive and Sexual Health Programme (ARSH) to make the adolescent girls free from infection by the time of pregnancy so as to achieve the goal.     

Regulation of expression of antioxidant enzymes by vitamin E and curcumin in <Emphasis Type="SmallCaps">l</Emphasis>-thyroxine-induced oxidative stress in rat renal cortex

The present study investigates the antioxidative effects of vitamin E and curcumin against l-thyroxine (T₄)-induced oxidative stress in renal cortex of adult male rats. Rats were made hyperthyroid by administration of l-thyroxine (0.0012%) in their drinking water for 30 days. Vitamin E (200 mg/kg body weight/day) and curcumin (30 mg/kg body weight/day) were supplemented singly or in combination orally for 30 days along with l-thyroxine treatment. The elevated level of oxidative stress parameters (lipid peroxidation and protein carbonylation) and decline level of small antioxidant molecules (reduced glutathione and ascorbic acid) in renal cortex of T₄-treated rats were restored back by supplementation of vitamin E or/and curcumin. Increased superoxide dismutase and catalase activities in kidney cortex of T₄-treated rats were ameliorated in response to vitamin E or/and curcumin treatment. The elevated translated product of Cu/Zn-SOD, Mn-SOD and catalase in T₄-treated rats were differentially reduced by the administration of vitamin E and curcumin independently or in combination. Cu/Zn-SOD expression was ameliorated by both vitamin E and curcumin independently or in combination, whereas Mn-SOD expression was ameliorated by the supplementation of vitamin E or curcumin independently. However, the expression of catalase was alleviated by only supplementation of vitamin E to T₄-treated rats. The results suggest that both vitamin E and curcumin may play an important role in protecting T₄-induced oxidative stress in rat renal cortex by differentially modulating the activities of antioxidant enzymes and oxidative stress parameters.     

A Novel Form of Stereo Vision in the Praying Mantis

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Structural Consequences of D481N/K483Q Mutation at Glycine Binding Site of NMDA Ionotropic Glutamate Receptors: A Molecular Dynamics Study

Abstract

N-Methyl-D-Aspartate (NMDA) receptors are the ligand gated as well as voltage sensitive ionotropic glutamate receptors, widely distributed in the vertebrate central nervous system and they play critical role in the pathogenesis of schizophrenia. Molecular dynamics simulations have been carried out on high resolution crystal structure of NR1 subunit of NMDA receptor ligand binding core (S1S2) in four different conformations. We have investigated consequence of D481N/K483Q double mutation of NR1 subunit from simulation results of (a) glycine bound form (WG), (b) unbound (closed-apo) form (WOG), (c) a double mutated form (DM), and (d) the antagonist (5,7-dichlorokynuric acid) bound form (DCKA). The MD simulations and simulated annealing for 4ns show a distinct conformation for the double mutated conformation that neither follows the antagonist nor apo conformation. There are two distinct sites, loop1 and loop2 where the double mutated structure in its glycine bound form shows significant RMSD deviations as compared to the wild-type. The interactions of glycine with the receptor remain theoretically unchanged in the double mutated structure and there is no detachment of S1S2 domains. The results suggest that separation of S1 and S2 domains may not be essential for channel inactivation. Therefore, it is hypothesized that hypoactivation of NMDA receptor channels may arise out of the conformational changes at non-conserved Loop1 and Loop2 regions observed in the mutated structure. The Loop1 and Loop2 regions responsible for inter-subunit interactions in a functional NMDA receptor, may therefore, render the ligand bound form defunct. This may account for behavioral anomalies due to receptor inactivation seen in grin1 mutated mice.     

Ternary complexes in solution with hydrogen phosphate and methyl phosphate as ligands

The stability constants of the 1:1 complexes formed between Cu(Arm)²⁺, where Arm = 2,2′-bipyridyl or 1,10-phenanthroline, and methyl phosphate, CH₃OPO₃²⁻, or hydrogen phosphate, HOPO₃²⁻, were determined by potentiometric pH titration in aqueous solution (25°C; l = 0.1 M, NaNO₃). On the basis of previously established log K versus pK_a straight-line plots (D. Chen et al., J. Chem. Soc., Dalton Trans. (1993) 1537–1546) for the complexes of simple phosphate monoesters and phosphonate derivatives, R-PO₃²⁻, where R is a non-coordinating residue, it is shown that the stabilities of the Cu(Arm) (CH₃OPO₃) complexes are solely determined by the basicity of the -PO₃²⁻ residue. In contrast, the Cu(Arm) (HOPO₃) complexes are slightly more stable (on average by 0.15 log unit) than expected on the basicity of HPO₄²⁻; this is possibly due to a more effective solvation including hydrogen bonding, an interaction not possible with coordinated CH₃OPO₃²⁻ species. Regarding biological systems the observation that HOPO₃²⁻ is somewhat favored over R-PO₃²⁻ species in metal ion interactions is meaningful.     

Selective attention in a synchronising bushcricket: physiology,behaviour and ecology

Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.