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• Imidacloprid alters the response of the DCMD to looming stimuli

• Agonizes nAChRs on the DCMD or upstream neurons (LGMD,

sensory cells)

• Bimodal response types:

• Responders: four phases of imidacloprid effect

• Non-responders: pre-response and recovery phases only

• Phases of imidacloprid effect:

• Pre-response: resembles control approaches, characterized by a

short decay phase, and maximum firing rate ~ 0.03s before TOC

• Hyperexcitation: high frequency, tonic firing of DCMD, not in

response to stimulus

• No response: DCMD ceases firing for a period

• Recovery: DCMD responds to stimulus, but PSTH characterized

by long decay phase, later peak time, and lower maximum rate.

• Long decay phase suggests imidacloprid alters inhibitory network.

• Future research:

• Rising phase of PSTH (appears to shorten in recovery phase)

• Longer-term effects of imidacloprid and metabolites

Since their introduction in the 1990s, neonicotinoids have been

commercialized as a miracle pesticide with low toxicity to mammals, low

risk of bioaccumulation, high toxicity to target insects, and convenient

function as systemic pesticides.1 Recently neonicotinoids have been

receiving negative attention due to their effects on non-target organisms,

especially birds and bees.2 Neonicotinoids are nicotine mimics, and act as

agonists to nicotinic acetylcholine receptors (nAChRs) present on insect

neurons.3

The locust (Locusta migratoria) is one of the most devastating agricultural

pests due to its ability to form high-density, mobile swarms.4 While the

locust is not a typical target organism for neonicotinoid pesticides, it is a

model organism in neuroethology. Two widely studied pairs of neurons,

which code visual information from each of the locust’s eyes and synapse

downstream with muscles involved with flight and jumping, are especially

sensitive to looming stimuli.5-7 Each lobula giant movement detector

(LGMD) receives visual information from the sensory cells of the

ommatidia, and synapses directly with the descending contralateral

movement detector (DCMD) at a one-to-one ratio.8

The present study aimed to determine if the neonicotinoid imidacloprid has

an effect on the response of the DCMD to a looming stimulus. If

imidacloprid binds to the DCMD or other upstream neurons, then the firing

rate and other response parameters may be altered.

1. INTRODUCTION

4. FIRING PROPERTIES

3. RAW TRACES & PERISTIMULUS TIME HISTOGRAMS 5. HISTOGRAM SHAPE PROPERTIES

6. SUMMARY

7. ACKNOWLEDGEMENTS & REFERENCESAcknowledgements

Funding provided by Department of Biology at the University of Saskatchewan for the summer of

2014. Thank you to Glyn McMillan for countless hours of advice and guidance.

References1. Bonmatin, J. M., et al. (2015). Environmental fate and exposure; neonicotinoids and fipronil. Environ. Sci. Pollut. Res. 22, 35–67.

2. Main, A. R., Headley, et al. (2014). Widespread use and frequent detection of neonicotinoid insecticides in wetlands of Canada’s Prairie Pothole Region. PLoS One 9,

e92821.

3. Tomizawa, M. and Casida, J. E. (2005). Neonicotinoid insecticide toxicology: mechanisms of selective action. Annu. Rev. Pharmacol. Toxicol. 45, 247–68.

4. Burrows, M. (1996). The neurobiology of an insect brain. New York, NY: Oxford University Press Inc.

5. Judge, S. and Rind, F. (1997). The locust DCMD, a movement-detecting neurone tightly tuned to collision trajectories. J. Exp. Biol. 200, 2209–2216

6. Gabbiani, F., Krapp, H. and Laurent, G. (1999). Computation of object approach by a wide-field, motion-sensitive neuron. J. Neurosci. 19, 1122–1141.

7. Gray, J. R., Robertson, R. M. and Lee, J. K. (2001). Activity of descending contralateral movement detector neurons and collision avoidance behaviour in response

to head-on visual stimuli in locusts. J. Comp. Physiol. A Sensory, Neural, Behav. Physiol. 187, 115–129.

8. Rind, F. C. (1984). A chemical synapse between two motion detecting neurones in the locust brain. J. Exp. Biol. 110, 143–167.

A neonicotinoid pesticide affects the firing properties of a looming-sensitive neuron in Locusta migratoria

Rachel Parkinson and John R. Gray, Dept. Biology, University of Saskatchewan

0

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-1.5 -1 -0.5 0 0.5

Fre

qu

ency

(sp

ikes

/s)

Time Relative to TOC (s)

Decay phase

Peak

Peak width

at half height

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Pre-response

Hyperexcitation

Recovery

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Recovery

Control

A B

C A: Raw trace and peristimulus time histogram (PSTH)

for a control loom. Maximum firing rate, peak time,

peak width at half height (Pw½h), and decay phase

marked.

B: Raw traces and PSTH overlays for three phases of

imidacloprid effect: pre-response (resembles control);

hyperexcitation; (sporadic firing); and recovery. Not

pictured: no response phase (inactivity of DCMD).

C: PSTH overlays of one recovery phase loom from

each animal (n=23) and all control looms (T01)

(n=96). Recovery phase characterized by a long decay,

lower peak, and slightly later peak time for the

recovery looms.

0 20 40 60 80

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T01 T02 T03 T04 non T04 respond.0

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T01 T02 T03 T04

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firin

g r

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(%

mea

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on

trol)

0 20 40 60 80 0 20 40 60 80Approach time (minutes)

0 20 40 60 80Approach time (minutes)

# S

pik

es (

% m

ean

con

trol)

# S

pik

es (

% m

ean

con

trol)

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Max.

firin

g r

ate

(n

orm

.)

Treatment Group

Treatment Group

T01 T02 T03 T04 non T04 respond. T01 T02 T03 T04 non T04 respond.

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OC

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T01 T02 T03 T04Treatment Group

T01 T02 T03 T04

T01 T02 T03 T04 T01 T02 T03 T04

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Approach time (minutes)

Dec

ay

ph

ase

(%

mea

n c

on

trol)

T01 T02 T03 T04 non T04 respond.

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Approach time (minutes)

T01 T02 T03 T04Treatment Group

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T01 T02 T03 T04 T01 T02 T03 T04 A B

A: Pw½h for all animals, normalized as a percent of the mean of T01, versus approach time, and

means (top). T04 responders display a decrease in Pw½h within 10 minutes of injection, followed by a

partial or full recovery. Significance of is denoted by alternate letter (bottom).

B: Decay phase for all animals versus approach time, and mean (top). Throughout T04 the decay phase

lengthens for all animals (bottom)

120

80

40

0Pw

½h

(%

mean

con

trol)

a a a ab

a a a

b

a aa

ab

a abb

c

d

aa a

b

2. METHODS

A

B

C

Treatment Description# approaches

(2.5 min apart)

T01 After 20 minutes acclimation 5 (0-10 min)

T02 After piercing cuticle with

microsyringe

5 (12.5-22.5 min)

T03 After injecting 200 µl saline 5 (25-35 min)

T04 After injecting 200 ng

imidacloprid in 200 µl saline

15 to 20 (37.5 min

onwards)

Injection

site

A: Maximum firing rate per approach, normalized as

a percent of the mean of T01, versus approach time.

Bimodal responses occurred (means plotted). Half of

animals experienced a sharp decrease in firing rate

within 10 minutes of injection of imidacloprid,

which then recovered to near or slightly lower than

pre-injection rates (top). Means of each group in

bold. Significance denoted by alternate letter

(bottom).

B: Number of spikes (normalized) versus approach

time for all animals, and mean (top). Similar

bimodal response types observed, but with increased

variability between treatment groups (bottom).

C: Peak time in relation to TOC as a function of

approach time for all animals, plus mean.

Throughout T04 peak time approaches TOC, with

the median of T04 significantly later than all other

groups (bottom).

DCMD

recordings

Stimulus

generation

LCD

projector

Video signal

Synch.

pulses191.5 cm

12 cm

Locust

Rear projection

dome screen

Data collection

and analysis

Rigid tetherSingle hook electrode

0º

180º

600 cm

90º7 cm

300 cm s-1

Approach time (minutes)

140

100

60

20

0