Biology subjects

Rabeler, C.

Publications and source records attributed to Rabeler, C..

8 recordsLinked to original sources

bioRxiv2026

Modulation of planarian seizure-like activity via antiseizure medications

Acute chemical exposure to organophosphorus compounds (OPs) arising from terrorist attacks or accidental poisonings pose a serious threat to human health. Acetylcholinesterase inhibition due to acute OP exposure causes a cholinergic crisis, manifested as increased secretions, respiratory distress, loss of consciousness, seizures, and ultimately death if left untreated. Benzodiazepines, such as midazolam, are currently used to stop OP-induced seizures, but must be administered within minutes after exposure to be effective. This makes midazolam impractical for large-scale civilian emergencies. Thus, there is a need to identify novel antiseizure medications (ASMs) that are equally effective even when administered later. It has been challenging to identify such compounds with traditional mammalian testing; high throughput screening assays that can quickly and cost-effectively evaluate many candidates for their potential as an ASM are needed. Planarians are aquatic invertebrates that are suitable organismal models for OP neurotoxicity studies due to the conservation of OP targets and their ability to metabolize OPs. Here, we built on our prior work that introduced a computational image analysis pipeline to quantify planarian seizure-like activity (pSLA) in two planarian species (Dugesia japonica and Girardia dorotocephala). We previously used this approach to characterize pSLA following acute exposure (up to 30 minutes) to seizurogenic compounds. In the present study, we asked whether pSLA induced by the OP pesticide parathion, pentylenetetrazole, or NMDA could be rescued by co-exposure to four ASMs: midazolam, topiramate, MK-801, and carbamazepine. All tested ASMs were effective at reducing parathion-induced pSLA in one planarian species. However, ASM responses varied substantially across proconvulsants and planarian species. Defining the molecular mechanisms underlying pSLA will be essential for establishing planarians as a reliable model for ASM discovery.

pharmacology and toxicology↗

bioRxiv2025

Planarian behavioral screening is a useful invertebrate model for evaluating seizurogenic chemicals

Detecting adverse health effects of drugs and other chemicals early during chemical/drug development saves significant time and resources. Freshwater planarians are an emerging invertebrate model for rapid, cost-effective neurotoxicity screening. Because planarians exhibit seizure-like behavior when exposed to chemicals that cause seizures in mammals, such as N-methyl-D-aspartate (NMDA) and picrotoxin, they could be a useful first-tier model for seizure screening and thus reduce the need for slow and expensive mammalian tests. However, planarian seizure studies to date have been low-throughput and lacking the necessary standardization and automated analysis to make this model a viable screening solution. Here, we present results from medium-throughput behavioral testing conducted in 48-well plates using two popular models for planarian pharmacological and toxicological studies: Dugesia japonica and Girardia dorotocephala. Planarian behavior was scored using automated image analysis, measuring both translational behavior and body shape changes. We found that known seizurogenic compounds in mammals (NMDA, nicotine, picrotoxin, pilocarpine, and pentylenetetrazole (PTZ)) induced seizure-like behavior in both planarian species within 30 minutes of exposure. We also tested three pesticides (parathion, carbaryl, and permethrin). Parathion and carbaryl, but not permethrin, caused planarian seizure-like activity. While the planarian species responded similarly to most compounds, some compounds showed potency differences of 10-100-fold (pilocarpine and nicotine, respectively). G. dorotocephala planarians were generally more sensitive, but D. japonica planarians displayed more reproducible behaviors. By standardizing both experimental approach and analysis methods and making them available, this work can serve as a framework for future testing of chemicals for seizurogenic potential in planarians.

pharmacology and toxicology↗

bioRxiv2022

Adult and regenerating planarians respond differentially to chronic drug exposure

There is a lack of data on the effects of chronic exposure to common drugs and stimulants on the developing nervous system. Freshwater planarians have emerged as a useful invertebrate model amenable to high-throughput behavioral phenotyping to assay chemical safety in adult and developing brains. Here, we leverage the unique strength of the system to test in parallel for effects on the adult and developing nervous system, by screening ten common drugs and stimulants (forskolin, clenbuterol, LRE-1, MDL-12,330A, adenosine, caffeine, histamine, mianserin, fluoxetine and sertraline) using the asexual freshwater planarian Dugesia japonica. The compounds were tested up to 100 {micro}M nominal concentration for their effects on planarian morphology and behavior. Quantitative phenotypic assessments were performed on days 7 and 12 of exposure using an automated screening platform. The antidepressants sertraline and fluoxetine were the most potent to induce lethality, with significant lethality observed at 10 {micro}M. All ten compounds caused sublethal morphological and/or behavioral effects, with the most effects, in terms of potency and breadth of endpoints affected, seen with mianserin and fluoxetine. Four of the compounds (forskolin, clenbuterol, mianserin, and fluoxetine) were developmentally selective, causing effects at lower concentrations in regenerating planarians. Of these, fluoxetine showed the greatest differences between the two developmental stages, inducing many behavioral endpoints in regenerating planarians but only a few in adult planarians. While some of these behavioral effects may be due to neuroefficacy, these results substantiate the need for better evaluation of the safety of these common drugs on the developing nervous system.

pharmacology and toxicology↗

bioRxiv2022

Bioactivation and detoxification of organophosphorus pesticides in freshwater planarians shares similarities with humans

Organophosphorus pesticides (OPs) are a chemically diverse class of insecticides that inhibit acetylcholinesterase (AChE). Many OPs require bioactivation to their active oxon form via cytochrome P450 to effectively inhibit AChE. OP toxicity can be mitigated by detoxification reactions performed by carboxylesterase and paraoxonase. The relative extent of bioactivation to detoxification varies among individuals and between species, leading to differential susceptibility to OP toxicity. Because of these species differences, it is imperative to characterize OP metabolism in model systems used to assess OP toxicity to adequately evaluate potential human hazard. We have shown that the asexual freshwater planarian Dugesia japonica is a suitable model to assess OP neurotoxicity and developmental neurotoxicity via rapid, automated testing of adult and developing organisms in parallel using morphological and behavioral endpoints. D. japonica has two cholinesterase enzymes with intermediate properties between AChE and butyrylcholinesterase that are sensitive to OP inhibition. Here, we demonstrate that this planarian contains the major OP metabolic machinery to be a relevant model for OP neurotoxicity studies. Adult and regenerating D. japonica can bioactivate chlorpyrifos and diazinon into their respective oxons. Significant AChE inhibition was only observed after in vivo metabolic activation but not when the parent OPs were directly added to planarian homogenate. Additionally, we found that D. japonica has both carboxylesterase and paraoxonase activity. Using specific chemical inhibitors, we show that carboxylesterase activity is distinct from cholinesterase activity. Taken together, these results further support the use of D. japonica for OP toxicity studies.

pharmacology and toxicology↗

bioRxiv2022

Differences in neurotoxic outcomes of organophosphorus pesticides revealed via multi-dimensional screening in adult and regenerating planarians

Organophosphorus pesticides (OPs) are a chemically diverse class of commonly used insecticides. Epidemiological studies suggest that low dose chronic prenatal and infant exposures can lead to life-long neurological damage and behavioral disorders. While inhibition of acetylcholinesterase (AChE) is the shared mechanism of acute OP neurotoxicity, OP-induced developmental neurotoxicity (DNT) can occur independently and/or in the absence of significant AChE inhibition, implying that OPs affect alternative targets. Moreover, different OPs can cause different adverse outcomes, suggesting that different OPs act through different mechanisms. These findings emphasize the importance of comparative studies of OP toxicity. Freshwater planarians are an invertebrate system that uniquely allows for automated, rapid and inexpensive testing of adult and developing organisms in parallel to differentiate neurotoxicity from DNT. Effects found only in regenerating planarians would be indicative of DNT, whereas shared effects may represent neurotoxicity. We leverage this unique feature of planarians to investigate potential differential effects of OPs on the adult and developing brain by performing a comparative screen to test 7 OPs (acephate, chlorpyrifos, dichlorvos, diazinon, malathion, parathion and profenofos) across 10 concentrations in quarter-log steps. Neurotoxicity was evaluated using a wide range of quantitative morphological and behavioral readouts. AChE activity was measured using an Ellman assay. The toxicological profiles of the 7 OPs differed across the OPs and between adult and regenerating planarians. Toxicological profiles were not correlated with levels of AChE inhibition. Twenty-two "mechanistic control compounds" known to target pathways suggested in the literature to be affected by OPs (cholinergic neurotransmission, serotonin neurotransmission, endocannabinoid system, cytoskeleton, adenyl cyclase and oxidative stress) and 2 negative controls were also screened. When compared with the mechanistic control compounds, the phenotypic profiles of the different OPs separated into distinct clusters. The phenotypic profiles of adult vs regenerating planarians exposed to the OPs clustered differently, suggesting some developmental-specific mechanisms. These results further support findings in other systems that OPs cause different adverse outcomes in the (developing) brain and build the foundation for future comparative studies focused on delineating the mechanisms of OP neurotoxicity in planarians.

pharmacology and toxicology↗

bioRxiv2022

Head Removal Enhances Planarian Electrotaxis

Sensing electric fields is an ability that certain animal species utilize for communication, hunting, and spatial orientation. Freshwater planarians move toward the cathode in a static electric field (cathodic electrotaxis). First described by Raymond Pearl more than a century ago, planarian electrotaxis has received little attention and the underlying mechanisms and evolutionary significance remain unknown. We developed an apparatus and scoring metrics for automated quantitative and mechanistic studies of planarian behavior upon exposure to a static electric field. Using this automated setup, we characterized electrotaxis in the planarian Dugesia japonica and found that this species responds to voltage instead of to current, in contrast to results from previous studies using other species. Because longer planarians exhibited more robust electrotaxis than shorter planarians, we hypothesized that signals from the head impede cathodic electrotaxis. To test this hypothesis, we took advantage of the regenerative abilities of planarians and compared electrotaxis in head and tail fragments of various lengths. We found that tail and trunk fragments electrotaxed while head fragments did not, regardless of size. However, we could restore cathodic electrotaxis in head fragments via decapitation, demonstrating that the presence of the head impaired cathodic electrotaxis. This result is in stark contrast to other stimulated behaviors such as phototaxis, thermotaxis or chemotaxis, which are weaker or absent in headless fragments. Thus, electrotaxis may be an important ability of headless planarian fragments to support survival prior to head regeneration. Summary statementWe present a new method for quantitative studies of planarian electrotaxis and show that Dugesia japonica move toward the cathode. This behavior is enhanced by removal of the head.

animal behavior and cognition↗

bioRxiv2020

Dugesia japonica is the best suited of three planarian species for high-throughput toxicology screening

High-throughput screening (HTS) using new approach methods is revolutionizing toxicology. Asexual freshwater planarians are a promising invertebrate model for neurotoxicity HTS because their diverse behaviors can be used as quantitative readouts of neuronal function. Currently, three planarian species are commonly used in toxicology research: Dugesia japonica, Schmidtea mediterranea, and Girardia tigrina. However, only D. japonica has been demonstrated to be suitable for HTS. Here, we assess the two other species for HTS suitability by direct comparison with D. japonica. Through quantitative assessments of morphology and multiple behaviors, we assayed the effects of 4 common solvents (DMSO, ethanol, methanol, ethyl acetate) and a negative control (sorbitol) on neurodevelopment. Each chemical was screened blind at 5 concentrations at two time points over a twelve-day period. We obtained two main results: First, G. tigrina and S. mediterranea planarians showed significantly reduced movement compared to D. japonica under HTS conditions, due to decreased health over time and lack of movement under red lighting, respectively. This made it difficult to obtain meaningful readouts from these species. Second, we observed species differences in sensitivity to the solvents, suggesting that care must be taken when extrapolating chemical effects across planarian species. Overall, our data show that D. japonica is best suited for behavioral HTS given the limitations of the other species. Standardizing which planarian species is used in neurotoxicity screening will facilitate data comparisons across research groups and accelerate the application of this promising invertebrate system for first-tier chemical HTS, helping streamline toxicology testing.

pharmacology and toxicology↗

bioRxiv2019

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

In response to noxious stimuli, planarians cease their typical ciliary gliding and exhibit an oscillatory type of locomotion called scrunching. We have previously characterized the biomechanics of scrunching and shown that it is induced by specific stimuli, such as amputation, noxious heat, and extreme pH. Because these specific inducers are known to activate Transient Receptor Potential (TRP) channels in other systems, we hypothesized that TRP channels control scrunching. We found that chemicals known to activate TRPA1 (allyl isothiocyanate (AITC) and hydrogen peroxide) and TRPV (capsaicin and anandamide) in other systems induce scrunching in the planarian species Dugesia japonica and, except for anandamide, in Schmidtea mediterranea. To confirm that these responses were specific to either TRPA1 or TRPV, respectively, we tried to block scrunching using selective TRPA1 or TRPV antagonists and RNA interference (RNAi) mediated knockdown. Unexpectedly, co-treatment with a mammalian TRPA1 antagonist, HC-030031, enhanced AITC-induced scrunching by decreasing the latency time, suggesting an agonistic relationship in planarians. We further confirmed that TRPA1 in both species is necessary for AITC-induced scrunching using RNAi. Conversely, while co-treatment of a mammalian TRPV antagonist, SB-366791, also enhanced capsaicin-induced reactions in D. japonica, combined knockdown of two previously identified D. japonica TRPV genes (DjTRPVa and DjTRPVb) did not inhibit capsaicin-induced scrunching. Surprisingly, RNAi of either DjTRPAa or DjTRPVa/DjTRPVb disrupted scrunching induced by the endocannabinoid and TRPV agonist, anandamide. Overall, our results show that although scrunching induction can involve different initial pathways for sensing stimuli, this behaviors signature dynamical features are independent of the inducer, implying that scrunching is a stereotypical planarian escape behavior in response to various noxious stimuli that converge on a single downstream pathway. Understanding which aspects of nociception are conserved or not across different organisms can provide insight into the underlying regulatory mechanisms to better understand pain sensation.

animal behavior and cognition↗