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Freshwater planarians exhibit three gaits (gliding, peristalsis, and scrunching) that are distinguishable by quantitative behavioral analysis. We describe a method to induce scrunching using various noxious stimuli, quantification thereof, and distinction from peristalsis and gliding. Using gene knockdown, we demonstrate the specificity of scrunching as a quantitative phenotypic readout.
Freshwater planarians normally glide smoothly through ciliary propulsion on their ventral side. Certain environmental conditions, however, can induce musculature-driven forms of locomotion: peristalsis or scrunching. While peristalsis results from a ciliary defect, scrunching is independent of cilia function and is a specific response to certain stimuli, including amputation, noxious temperature, extreme pH, and ethanol. Thus, these two musculature-driven gaits are mechanistically distinct. However, they can be difficult to distinguish qualitatively. Here, we provide a protocol for inducing scrunching using various physical and chemical stimuli. We detail the quantitative characterization of scrunching, which can be used to distinguish it from peristalsis and gliding, using freely available software. Since scrunching is a universal planarian gait, albeit with characteristic species-specific differences, this protocol can be broadly applied to all species of planarians, when using appropriate considerations. To demonstrate this, we compare the response of the two most popular planarian species used in behavioral research, Dugesia japonica and Schmidtea mediterranea, to the same set of physical and chemical stimuli. Furthermore, the specificity of scrunching allows this protocol to be used in conjunction with RNA interference and/or pharmacological exposure to dissect the molecular targets and neuronal circuits involved, potentially providing mechanistic insight into important aspects of nociception and neuromuscular communication.
In addition to their popularity for stem cell and regeneration research1,2,3, freshwater planarians have long been used in behavioral studies4,5, taking advantage of their comparatively large size (a few millimeters in length), ease and low cost of laboratory maintenance, and broad spectrum of observable behaviors. The introduction of computer vision and automated tracking to planarian behavior studies6,7,8,9,10,11 have enabled quantitative differentiation of behavioral phenotypes. Animal behavior is a direct readout of neuronal function. Because the planarian nervous system is of medium size and complexity, but shares conserved key elements with the vertebrate brain12,13,14, studying planarian behavior can provide insight into conserved mechanisms of neuronal action which may be hard to directly probe in more complex organisms. Thus, planarians are a valuable model for comparative neurobiology studies8,12,15,16,17,18,19,20,21. In addition, the aquatic environment allows for rapid and facile exposure to chemicals to study their effect on brain function in regenerating and adult planarians, making them a popular system for neurotoxicology22,23,24,25,26.
Planarians possess three distinct gaits, referred to as gliding, peristalsis, and scrunching. Each gait is exhibited under specific circumstances: gliding is the default gait, peristalsis occurs when ciliary function is compromised7,27, and scrunching is an escape gait – independent of cilia function – in response to certain noxious stimuli7. We have shown that scrunching is a specific response, elicited by the sensation of certain chemical or physical cues, including extreme temperatures or pH, mechanical injury, or specific chemical inducers, and thus is not a general stress response7,28,29.
Because of its specificity and stereotypical parameters, which can easily be quantified using this protocol, scrunching is a powerful behavioral phenotype that enables researchers to perform mechanistic studies dissecting sensory pathways and neuronal control of behavior25,28. Additionally, scrunching has been shown to be a sensitive endpoint to assay adverse chemical effects on nervous system development and function in neurotoxicology studies22,24,25,30. As several different sensory pathways seem to converge to induce scrunching through various mechanisms28, scrunching differs from other planarian behaviors because various, but specific, stimuli can be used to dissect distinct neuronal circuits and study how different signals are integrated to produce the scrunching phenotype.
Importantly, species differences exist, wherein one chemical may elicit scrunching in one planarian species, but a different behavioral response in another. For example, we have found that anandamide induces scrunching in the planarian species Dugesia japonica but induces peristalsis in Schmidtea mediterranea28. This example highlights the importance of being able to reliably distinguish between the different gaits, because they are the phenotypic manifestations of distinct molecular mechanisms. However, distinction of scrunching from peristalsis is difficult using qualitative observational data, because both gaits are musculature-driven and share qualitative similarities7,28. Thus, to distinguish the gaits it is necessary to perform cilia imaging or a quantitative behavioral study, which allows distinction based on characteristic parameters7,28. Because cilia imaging is experimentally challenging and requires specialized equipment such as a high-magnification compound microscope and a high-speed camera7,28, it is not as broadly accessible to researchers as quantitative behavioral analysis.
Here, we present a protocol for (1) the induction of scrunching using various physical (noxious temperature, amputation, near-UV light) and chemical (allyl isothiocyanate (AITC), cinnamaldehyde) stimuli and (2) the quantitative analysis of planarian behavior using freely available software. By quantifying four parameters (frequency of body length oscillations, relative speed, maximum amplitude, and asymmetry of body elongation and contraction)7, scrunching can be differentiated from gliding, peristalsis, and other behavioral states reported in the literature, such as snake-like locomotion15 or epilepsies15. Furthermore, while scrunching is conserved among different planarian species7, each species has its own characteristic frequency and speed; therefore, once the gliding and scrunching speeds of a species have been determined, speed alone can be used as a means to distinguish scrunching from gliding and peristalsis29. The protocol assumes no prior training in computational image analysis or behavioral studies and thus can also be applied for planarian behavioral experiments in a teaching laboratory context at the undergraduate level. Example data to facilitate protocol adaptation is provided in the Supplemental Material.
1. Quantitative planarian behavior assays
2. Scrunching induction
Extraocular near-UV perception in S. mediterranea planarians is TRPA1-dependent and has been proposed to be linked to H2O2 release17. Because H2O2 exposure induces TRPA1-dependent scrunching in S. mediterranea and D. japonica planarians28, the steps in Section 2.1.4 can be used to test whether near-UV light exposure induces scrunching in both species. While D. japonica planarians scrunch (10/10)...
Using this protocol, one can quantitatively study the effects of physical and chemical stimuli7,28,29 or genetic manipulation (RNAi)28,29 on planarian locomotion. To maximize spatial resolution, it is best to move the camera as close as possible to the arena while ensuring the entire arena is in the field of view. To increase throughput, the behavior of multiple planaria...
The authors have nothing to disclose.
The authors thank Mr. Tapan Goel for comments on the manuscript. This work was funded by NSF CAREER Grant 1555109.
Name | Company | Catalog Number | Comments |
Allyl isothiocyanate, 95% (AITC) | Sigma-Aldrich | 377430-5G | CAUTION: Flammable and acutely toxic; handle in a fume hood with appropriate PPE. |
Camera lens, 2/3 25mm F/1.4 | Tamron | 23FM25SP | |
Cell culture plates, 6 well, tissue culture treated | Genesee Scientific | 25-105 | |
Centrifuge tubes, 50 mL polypropylene, sterile | MedSupply Partners | 62-1019-2 | |
Cinnamaldehyde, >95% | Sigma-Aldrich | W228613-100G-K | |
Dimmable A4 LED Tracer Light Box | Amazon | B07HD631RP | |
Flea3 USB3 camera | FLIR | FL3-U3-13E4M | |
Heat resistant gloves | Fisher Scientific | 11-394-298 | |
Hot plate | Fisher Scientific | HP88854200 | |
Instant Ocean Sea Salt, prepared in deionized water | Instant Ocean | SS15-10 | Prepare in deionized water at 0.5 g/L. |
Montjüic salts, prepared in Milli-Q water | Sigma-Aldrich | various | Prepare in milli-Q water at 1.6 mM NaCl, 1.0 mM CaCl2, 1.0 mM MgSO4, 0.1 mM MgCl2, 0.1 mM KCl, 1.2 mM NaHCO3; adjust pH to 7.0 with HCl. |
Petri dishes, 100 mm x 20 mm, sterile polystyrene | Simport | D210-7 | |
Pipette, 20-200 μL range | Rainin | 17008652 | |
PYREX 150 mL beaker | Sigma-Aldrich | CLS1000150 | |
Razor blade, 0.22 mm | VWR | 55411-050 | |
Roscolux color filter: Golden Amber | Rosco | R21 | Alternatively purchase the Roscolux Designer Color Selector (Musson Theatrical product #SBLUX0306) which includes all 3 color filters together. |
Roscolux color filter: Medium Red | Rosco | R27 | |
Roscolux color filter: Storaro Red | Rosco | R2001 | |
Samco transfer pipette, 62 µL large aperture | Thermo Fisher | 691TS | |
Support stand | Fisher Scientific | 12-947-976 | |
Thermometer | VWR | 89095-600 | |
UV laser pointer | Amazon | B082DGS86R | This is a Class II laser (405nm ±10nm) with output power <5 mW. |
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