Histamine alters environmental place preference in planaria

Conditioned Place Avoidance in the Planaria Schmidtea mediterranea: A Pre-clinical Invertebrate Model of Anxiety-Related Disorders

The objective of the present study was to develop a model of avoidance learning and its extinction in planarians (Schmidtea mediterranea). Based on previous experiments showing conditioned place preference, we developed a procedure to investigate conditioned place avoidance (CPA) using shock as an unconditioned stimulus (US) and an automated tracking system to record the animals' behaviour. In Experiment 1, we assessed the unconditioned properties of different shock intensities by measuring post shock activity. In two subsequent experiments we investigated CPA using different designs, surfaces as conditioned stimuli (CSs; rough and smooth), and different US intensities (5V and 10V). In general, we observed the successful development of CPA. However, CPA was stronger with higher shock intensities, and we found that, in our preparation, a rough surface is best at entering into an association with the shock than a smooth surface. Finally, we also observed extinction of CPA. The evidence of CPA and its extinction in flatworms validates the planaria as a pre-clinical model for the study of avoidance learning, a hallmark of anxiety disorders.

Kratom pharmacology: Clues from planarians exposed to mitragynine

Mitragynine (MG), the most prevalent bioactive alkaloid in kratom, displays nanomolar affinity for µ, κ and δ opioid receptors and produces opioid-dependent antinociception and dependence in rats. Here, using a battery of behavioral assays, we investigated MG effects in planarians. Acute MG exposure (< 100 μM) did not affect planarian motility or environmental preference, but reduced motility was detected during abstinence from chronic MG (1, 10 μM). MG (10 μM) produced place conditioning effects that were reduced by naltrexone (10  μΜ). These results suggest that MG produces opioid-sensitive reinforcing effects in planarians and MG pharmacology is conserved across different species.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.