Pharmacological or genetic targeting of Transient Receptor Potential (TRP) channels can disrupt the planarian escape response

Abstract

25In response to noxious stimuli, planarians cease their typical ciliary gliding and exhibit 26 an oscillatory type of locomotion called scrunching. We have previously characterized the 27 biomechanics of scrunching and shown that it is induced by specific stimuli, such as 28 amputation, noxious heat, and extreme pH. Because these specific inducers are known to 29 activate Transient Receptor Potential (TRP) channels in other systems, we hypothesized that 30 TRP channels control scrunching. We found that chemicals known to activate TRPA1 (allyl 31 isothiocyanate (AITC) and hydrogen peroxide) and TRPV (capsaicin and anandamide) in other 32 systems induce scrunching in the planarian species Dugesia japonica and, except for 33 anandamide, in Schmidtea mediterranea. To confirm that these responses were specific to 34 either TRPA1 or TRPV, respectively, we tried to block scrunching using selective TRPA1 or 35 TRPV antagonists and RNA interference (RNAi) mediated knockdown. Unexpectedly, co-36 treatment with a mammalian TRPA1 antagonist, HC-030031, enhanced AITC-induced 37 scrunching by decreasing the latency time, suggesting an agonistic relationship in planarians. 38 We further confirmed that TRPA1 in both species is necessary for AITC-induced scrunching 39 using RNAi. Conversely, while co-treatment of a mammalian TRPV antagonist, SB-366791, 40 also enhanced capsaicin-induced reactions in D. japonica, combined knockdown of two 41 previously identified D. japonica TRPV genes (DjTRPVa and DjTRPVb) did not inhibit 42 capsaicin-induced scrunching. Surprisingly, RNAi of either DjTRPAa or DjTRPVa/DjTRPVb 43 disrupted scrunching induced by the endocannabinoid and TRPV agonist, anandamide. 44 Overall, our results show that although scrunching induction can involve different initial 45 pathways for sensing stimuli, this behavior's signature dynamical features are independent of 46 the inducer, implying that scrunching is a stereotypical planarian escape behavior in response 47 to various noxious stimuli that converge on a single downstream pathway. Understanding 48 which aspects of nociception are conserved or not across different organisms can provide 49 3 insight into the underlying regulatory mechanisms to better understand pain sensation. 50 51 52Normal locomotion of freshwater planarians, termed gliding, is achieved through 53 synchronous beating of cilia in a layer of secreted mucus (1-3). Gliding planarians display a 54 smooth motion without major body shape changes, except for turning movements of the 55 anterior end. However, when exposed to certain noxious stimuli (e.g. low pH, high temperature, 56 or amputation), planarians switch to a muscular-based escape gait that is characterized by 57 oscillatory body length changes (4). We termed this gait scrunching and showed that it has a 58 characteristic set of 4 quantifiable parameters: 1. frequency of body length oscillations, 2. 59 relative speed, 3. maximum amplitude, and 4. asymmetry of body elongation and contraction 60 (4). Moreover, scrunching is conserve...

The Endocannabinoid System and Invertebrate Neurodevelopment and Regeneration

“…As mentioned, TRPV channel activation has been observed in response to anandamide in mammalian models [123,124]. A recent study demonstrated that two previously identified TRPV-encoding genes (DjTRPVa and DjTRPVb) partially mediate anandamide sensing in Dugesia japonica [122]. Exposure to 100 μM of anandamide resulted in the scrunching behaviour associated with noxious stimuli, as well as an unexpected increase in head lifting or head wiggling [122].…”

“…Planarians display what is known as "scrunching" in response to noxious stimuli, such as low pH, elevated temperatures, or amputation [121,122]. This behaviour is described as a ciliaindependent alteration in oscillatory gait, which is thought to be mediated through the TRP channels [121,122]. As mentioned, TRPV channel activation has been observed in response to anandamide in mammalian models [123,124].…”

“…Additional actions of cannabinoids in planaria may be mediated through TRP-like receptors. Planarians display what is known as "scrunching" in response to noxious stimuli, such as low pH, elevated temperatures, or amputation [121,122]. This behaviour is described as a ciliaindependent alteration in oscillatory gait, which is thought to be mediated through the TRP channels [121,122].…”

“…A recent study demonstrated that two previously identified TRPV-encoding genes (DjTRPVa and DjTRPVb) partially mediate anandamide sensing in Dugesia japonica [122]. Exposure to 100 μM of anandamide resulted in the scrunching behaviour associated with noxious stimuli, as well as an unexpected increase in head lifting or head wiggling [122]. When TRPV channels, DjTRPVa and DjTRPVb were knocked down via RNA interference, a decreased behavioral response associated with a delay in onset of scrunching was observed, highlighting the involvement of TRPV channels in anandamide-induced scrunching, but also supporting the involvement of other receptor(s) in anandamide sensing [122].…”

Head Removal Enhances Planarian Electrotaxis

“…Furthermore, because different researchers used different planarian species, varying experimental conditions and manual scoring metrics, which were rarely described in detail and may have suffered from experimenter bias (reviewed by (Jenkins, 1967) and summarized in Table S1), it is difficult to compile and interpret these previous findings. Therefore, we decided to revisit planarian electrotaxis with modern experimental tools and a quantitative and automated approach using the species Dugesia japonica, a popular species for planarian behavioral studies (Shomrat and Levin, 2013;Inoue, Yamashita and Agata, 2014;Inoue et al, 2015;Sabry et al, 2019;Zhang et al, 2019;Ireland et al, 2020;Le et al, 2021).…”