Placebo Analgesia in Rodents: Current and Future Research

Abstract

The investigation of placebo effects in animal pain models has received less attention than human research. This may be related to a number of difficulties, including the fact that animals lack the ability to use language and establish expectancies verbally, that animals cannot report and rate the extent to which they experience pain, and the inadequacy of current models of pain. Here, we describe the relatively small number of studies that have been published, communicating the opportunities and excitement of this research. We critically discuss pitfalls and limitations with the hope that this will advance future animal placebo-related research.

The Placebo Effect in Pain Therapies

“…The investigation of the placebo effect has been flourishing in human laboratory settings more than in animal research. This is not surprising given that placebo effects in animals can only be studied through physiological or pharmacological paradigms, whereas in humans verbally induced responses can also be investigated (reviewed in 82). The animal studies that have been conducted appear to corroborate the results from human studies.…”

In search of a rodent model of placebo analgesia in chronic orofacial neuropathic pain

“…To investigate true placebo effects, the inclusion of a no-treatment arm is essential to observe any non-specific changes. Ours is the first study to include a natural history group in animal models of placebo research (Keller et al, 2018) a sine qua non condition for separating drug from placebo effects and placebo responses (Colloca, 2019). Further, this is the first placebo study that combines a reflexive test for allodynia and the facial grimace test of ongoing neuropathic pain.…”

“…Placebo analgesia has primarily been investigated in clinical studies, and the handful of studies conducted in animals have mostly focused on models of acute pain (Keller et al, 2018). These studies have provided some evidence for the occurrence of conditioned placebo analgesia effects in rodents with acute pain.…”

Replikationskrise in der präklinischen Suchtforschung und Vorschläge zur Krisenbewältigung

“…Ein nicht zu unterschätzendes und bislang in der Literatur nicht erörtertes Translationsproblem ist der fehlende Placeboeff ekt bei tierexperimentellen Untersuchungen. Konditionierte Placeboeff ekte, insbesondere Placebo-induzierte Analgesie wurde bei Labortieren beschrieben (Herrenstein, 1962;Keller, Akintola & Colloca, 2018), jedoch kann es bei der Testung für pharmakologische Interventionen von somatischen und psychischen Erkrankungen, wie z. B. Suchterkrankungen nicht zum Auftreten eines Placeboeff ektes bei Versuchstieren kommen (es sein denn, sie würden durch das Pharmakon zunächst konditioniert; diese Möglichkeit ist jedoch aufgrund des Versuchsdesigns nicht gegeben).…”