The effect of retinal GABA Depletion by Allylglycineon mouse retinal ganglion cell responses to light

International audienceThe inhibitory neurotransmitter GABA (γ-aminobutyric acid) is metabolized by glutamic acid decarboxylase (GAD) which exists in two iso-forms in the mature CNS, GAD65 and GAD67. Allylglycine, a glycine derivative, is a nonspecific inhibitor of both GAD isoforms. Prolongedexposure to allylgycine can therefore deplete the tissue of endogenous GABA over time (Orlowski et al, 1977; Chabrol et al., 2012). Herewe applied Allylglycine (ALLYL) in vitro over several hours to gradually deplete GABA in the adult mouse retina and compared the effectsof GABA depletion on retinal ganglion cells (RGCs) receptive fields with those obtained by simultaneously blocking all GABAergic recep-tors (type A, B and C)

Pyrethroids and Nectar Toxins Have Subtle Effects on the Motor Function, Grooming and Wing Fanning Behaviour of Honeybees (Apis mellifera)

Sodium channels, found ubiquitously in animal muscle cells and neurons, are one of the main target sites of many naturally-occurring, insecticidal plant compounds and agricultural pesticides. Pyrethroids, derived from compounds found only in the Asteraceae, are particularly toxic to insects and have been successfully used as pesticides including on flowering crops that are visited by pollinators. Pyrethrins, from which they were derived, occur naturally in the nectar of some flowering plant species. We know relatively little about how such compounds—i.e., compounds that target sodium channels—influence pollinators at low or sub-lethal doses. Here, we exposed individual adult forager honeybees to several compounds that bind to sodium channels to identify whether these compounds affect motor function. Using an assay previously developed to identify the effect of drugs and toxins on individual bees, we investigated how acute exposure to 10 ng doses (1 ppm) of the pyrethroid insecticides (cyfluthrin, tau-fluvalinate, allethrin and permethrin) and the nectar toxins (aconitine and grayanotoxin I) affected honeybee locomotion, grooming and wing fanning behaviour. Bees exposed to these compounds spent more time upside down and fanning their wings. They also had longer bouts of standing still. Bees exposed to the nectar toxin, aconitine, and the pyrethroid, allethrin, also spent less time grooming their antennae. We also found that the concentration of the nectar toxin, grayanotoxin I (GTX), fed to bees affected the time spent upside down (i.e., failure to perform the righting reflex). Our data show that low doses of pyrethroids and other nectar toxins that target sodium channels mainly influence motor function through their effect on the righting reflex of adult worker honeybees

GTX Dose-Dependent Summary Statistics.

<p>GTX Dose-Dependent Summary Statistics.</p

Behaviours.

<p>Descriptions of behaviours recorded using Noldus Observer 5.0, over the ten min observation period.</p

Pyrethroid/Nectar Toxin Study Summary Statistics.

<p>P value and Chi-square values (with degrees of freedom indicated) for statistical analysis of grooming behaviour.</p

Acute effects of two concentrations of GTX (10 μM and 100 μM) on honeybee motor function and wing fanning.

<p>This figure illustrates how the different concentrations of GTX affect the percentage of time, number of bouts and mean duration of: (A-C) walking; (D-F) still; (G-I) upside down; (J-L) wing fanning. Sample size N = 16/treatment. * indicates P<0.05. [C = control, Ac = aconitine, Al = allethrin, GTX = grayanotoxin I, Cyf = cyfluthrin, Flu = tau-fluvalinate, Per = permethrin].</p

Chemical structures of compounds used in this study.

<p>(A) grayanotoxin I [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref038" target="_blank">38</a>]; (B) aconitine [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref039" target="_blank">39</a>]; (C) pyrethrin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref040" target="_blank">40</a>]; (D) allethrin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref041" target="_blank">41</a>]; (E) cyfluthrin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref021" target="_blank">21</a>]; (F) permethrin [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref022" target="_blank">22</a>]; (G) tau-fluvalinate [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref023" target="_blank">23</a>].</p

LD₅₀ Values and Concentrations of Compounds.

<p>LD₅₀ values of pyrethroids [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref005" target="_blank">5</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref021" target="_blank">21</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref023" target="_blank">23</a>] and their maximum detected concentrations in wax, pollen and bees as well as the total detected concentration [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0133733#pone.0133733.ref005" target="_blank">5</a>]. The mean LD₅₀ value was calculated and displayed when several LD₅₀ values had been reported in the literature.</p

Acute effects of pyrethroids and nectar toxins, at a dose of 10 ng/bee (37 ng/bee for grayanotoxin I), on honeybee grooming behaviour.

<p>This figure illustrates how compounds affected the percentage of time that bees spent: (A) grooming (pooled total of all grooming behaviours); (B) abdomen grooming; (C) leg grooming; (D) facial grooming (E) proboscis grooming; (F) antennal grooming. Sample size N = 16/treatment. * indicates P<0.05. [C = control, Ac = aconitine, Al = allethrin, GTX = grayanotoxin I, Cyf = cyfluthrin, Flu = tau-fluvalinate, Per = permethrin].</p