R Zurich, University of Zurich and Swiss Federal Institute of Technology Zurich, CH-8058 Zurich, Switzerland Division of Psychology, University of Fribourg, CH-1700 Fribourg, Switzerland; [email protected] Correspondence: [email protected] or [email protected]: Cumming, P.; Scheidegger, M.; Dornbierer, D.; Palner, M.; Quednow, B.B.; Martin-Soelch, C. molecular and Functional κ Opioid Receptor/KOR Species imaging Studies of Psychedelic Drug Action in Animals and Humans. Molecules 2021, 26, 2451. https://doi.org/10.3390/ molecules26092451 Academic Editors: Mauricio Morais and P er Kele Received: eight March 2021 Accepted: 19 April 2021 Published: 22 AprilPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Copyright: 2021 by the authors. Licensee MDPI, Basel, Switzerland. This short article is definitely an open access short article distributed beneath the terms and circumstances with the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).Abstract: Hallucinogens are a loosely defined group of compounds including LSD, N,Ndimethyltryptamines, mescaline, psilocybin/psilocin, and 2,5-dimethoxy-4-methamphetamine (DOM), which can evoke intense visual and emotional experiences. We’re witnessing a renaissance of investigation interest in hallucinogens, driven by growing awareness of their psychotherapeutic potential. As such, we now present a narrative evaluation with the literature on hallucinogen binding in vitro and ex vivo, as well as the various molecular imaging studies with positron emission tomography (PET) or single photon emission computer system tomography (SPECT). In general, molecular imaging can depict the uptake and binding distribution of labelled COMT Molecular Weight hallucinogenic compounds or their congeners in the brain, as was shown in an early PET study with N1 -([11 C]-methyl)-2-bromo-LSD ([11 C]-MBL); displacement using the non-radioactive competitor ketanserin confirmed that the majority of [11 C]-MBL particular binding was to serotonin 5-HT2A receptors. Having said that, interactions at serotonin 5HT1A and other classes of receptors and pleotropic effects on second messenger pathways may contribute to the particular experiential phenomenologies of LSD along with other hallucinogenic compounds. Other salient elements of hallucinogen action include things like permeability towards the blood rain barrier, the prices of metabolism and elimination, along with the formation of active metabolites. In spite of the maturation of radiochemistry and molecular imaging in recent years, there has been only a handful of PET or SPECT studies of radiolabeled hallucinogens, most not too long ago making use of the 5-HT2A/2C agonist N-(2[11 CH3 O]methoxybenzyl)-2,5-dimethoxy- 4-bromophenethylamine ([11 C]Cimbi-36). As well as PET research of target engagement at neuroreceptors and transporters, there is a compact variety of studies around the effects of hallucinogenic compounds on cerebral perfusion ([15 O]-water) or metabolism ([18 F]fluorodeoxyglucose/FDG). There remains considerable scope for standard imaging research on the web pages of interaction of hallucinogens and their cerebrometabolic effects; we expect that hybrid imaging with PET in conjunction with functional magnetic resonance imaging (fMRI) need to give especially helpful for the following phase of this research. Keywords and phrases: hallucinogens; molecular imaging; PET; SPECT; serotonin receptorsMolecules 2021, 26, 2451. https://doi.org/10.3390/moleculeshttps://www.mdpi.com/journal/moleculesMolecules 2021, 26,2 ofContents: 1.