OPEN Foundation

G. Knudsen

A Single Dose of Psilocybin Increases Synaptic Density and Decreases 5-HT 2A Receptor Density in the Pig Brain

February 6, 2022 / Depression, Mushrooms / Psilocybin, Neuroscience, Papers / Leave a Comment / By / , , , , , ,

Abstract

A single dose of psilocybin, a psychedelic and serotonin 2A receptor (5-HT2AR) agonist, may be associated with antidepressant effects. The mechanism behind its antidepressive action is unknown but could be linked to increased synaptogenesis and down-regulation of cerebral 5-HT2AR. Here, we investigate if a single psychedelic dose of psilocybin changes synaptic vesicle protein 2A (SV2A) and 5-HT2AR density in the pig brain. Twenty-four awake pigs received either 0.08 mg/kg psilocybin or saline intravenously. Twelve pigs (n = 6/intervention) were euthanized one day post-injection, while the remaining twelve pigs were euthanized seven days post-injection (n = 6/intervention). We performed autoradiography on hippocampus and prefrontal cortex (PFC) sections with [3H]UCB-J (SV2A), [3H]MDL100907 (5-HT2AR antagonist) and [3H]Cimbi-36 (5-HT2AR agonist). One day post psilocybin injection, we observed 4.42% higher hippocampal SV2A density and lowered hippocampal and PFC 5-HT2AR density (-15.21% to -50.19%). These differences were statistically significant in the hippocampus for all radioligands and in the PFC for [3H]Cimbi-36 only. Seven days post-intervention, there was still significantly higher SV2A density in the hippocampus (+9.24%) and the PFC (+6.10%), whereas there were no longer any differences in 5-HT2AR density. Our findings suggest that psilocybin causes increased persistent synaptogenesis and an acute decrease in 5-HT2AR density, which may play a role in psilocybin’s antidepressive effects.

Raval, N. R., Johansen, A., Donovan, L. L., Ros, N. F., Ozenne, B., Hansen, H. D., & Knudsen, G. M. (2021). A Single Dose of Psilocybin Increases Synaptic Density and Decreases 5-HT2A Receptor Density in the Pig Brain. International journal of molecular sciences, 22(2), 835. https://doi.org/10.3390/ijms22020835

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Effects of a single dose of psilocybin on behaviour, brain 5-HT 2A receptor occupancy and gene expression in the pig

January 21, 2022 / Mushrooms / Psilocybin, Neuroscience, Papers, Psychopharmacology / Leave a Comment / By / , , , , , , , , ,

Abstract

Psilocybin has in some studies shown promise as treatment of major depressive disorder and psilocybin therapy was in 2019 twice designated as breakthrough therapy by the U.S. Food and Drug Administration (FDA). A very particular feature is that ingestion of just a single dose of psilocybin is associated with lasting changes in personality and mood. The underlying molecular mechanism behind its effect is, however, unknown. In a translational pig model, we here present the effects of a single dose of psilocybin on pig behaviour, receptor occupancy and gene expression in the brain. An acute i.v. injection of 0.08 mg/kg psilocybin to awake female pigs induced characteristic behavioural changes in terms of headshakes, scratching and rubbing, lasting around 20 min. A similar dose was associated with a cerebral 5-HT2A receptor occupancy of 67%, as determined by positron emission tomography, and plasma psilocin levels were comparable to what in humans is associated with an intense psychedelic experience. We found that 19 genes were differentially expressed in prefrontal cortex one day after psilocybin injection, and 3 genes after 1 week. Gene Set Enrichment Analysis demonstrated that multiple immunological pathways were regulated 1 week after psilocybin exposure. This provides a framework for future investigations of the lasting molecular mechanisms induced by a single dose of psilocybin. In the light of an ongoing debate as to whether psilocybin is a safe treatment for depression and other mental illnesses, it is reassuring that our data suggest that any effects on gene expression are very modest.

Donovan, L. L., Johansen, J. V., Ros, N. F., Jaberi, E., Linnet, K., Johansen, S. S., Ozenne, B., Issazadeh-Navikas, S., Hansen, H. D., & Knudsen, G. M. (2021). Effects of a single dose of psilocybin on behaviour, brain 5-HT2A receptor occupancy and gene expression in the pig. European neuropsychopharmacology : the journal of the European College of Neuropsychopharmacology, 42, 1–11. https://doi.org/10.1016/j.euroneuro.2020.11.013

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Brain serotonin 2A receptor binding predicts subjective temporal and mystical effects of psilocybin in healthy humans

February 6, 2022 / Mushrooms / Psilocybin, Neuroscience, Papers, Psychopharmacology, Spirituality / Leave a Comment / By / , , , , , , ,

Abstract

Background: Psilocybin is a serotonergic psychedelic with psychoactive effects mediated by serotonin 2A receptor (5-HT2AR) activation. It produces an acute psychedelic altered state of consciousness with a unique phenomenology that can be temporally characterized by three intensity phases: onset of psychoactive effect, a peak plateau and return to normal consciousness.

Aims: We evaluated whether pre-drug brain 5-HT2AR binding predicted the three phases of psilocybin subjective drug intensity (SDI) and retrospective self-report of mystical type experiences in healthy individuals.

Method: Sixteen participants completed a pre-drug [11C]Cimbi-36 positron emission tomography scan to assess 5-HT2AR binding. On a separate day, participants completed a single psilocybin session (oral dose range 0.2-0.3 mg/kg), during which SDI was assessed every 20 min. The Mystical Experience Questionnaire (MEQ) was completed at the end of the session. The three SDI phases were modelled using segmented linear regressions. We evaluated the associations between neocortex 5-HT2AR binding and SDI/MEQ outcomes using linear regression models.

Results: Neocortex 5-HT2AR was statistically significantly negatively associated with peak plateau duration and positively with time to return to normal waking consciousness. It was also statistically significantly negatively associated with MEQ total score.

Conclusion: This is the first study to investigate how individual brain 5-HT2AR binding predicts subjective effects of a single dose of psilocybin. Our findings reinforce the role of cerebral 5-HT2AR in shaping the temporal and mystical features of the psychedelic experience. Future studies should examine whether individual brain levels of 5-HT2AR have an impact on therapeutic outcomes in clinical studies.

Stenbæk, D. S., Madsen, M. K., Ozenne, B., Kristiansen, S., Burmester, D., Erritzoe, D., Knudsen, G. M., & Fisher, P. M. (2021). Brain serotonin 2A receptor binding predicts subjective temporal and mystical effects of psilocybin in healthy humans. Journal of psychopharmacology (Oxford, England), 35(4), 459–468. https://doi.org/10.1177/0269881120959609

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Plasma psilocin critically determines behavioral and neurobiological effects of psilocybin

August 25, 2020 / Chemistry, Medicine, Mushrooms / Psilocybin, Papers, Psychopharmacology, Psychotherapy, Publications, Safety / By / ,

Madsen, M. K., & Knudsen, G. M. (2021). Plasma psilocin critically determines behavioral and neurobiological effects of psilocybin. Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology, 46(1), 257-258; 10.1038/s41386-020-00823-4
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Dynamic coupling of whole-brain neuronal and neurotransmitter systems

April 13, 2020 / Anxiety disorders / PTSD, Depression, Mushrooms / Psilocybin, Neuroscience, Papers, Psychiatry, Psychology, Psychopharmacology, Publications / By / , , , , , ,

Abstract

Remarkable progress has come from whole-brain models linking anatomy and function. Paradoxically, it is not clear how a neuronal dynamical system running in the fixed human anatomical connectome can give rise to the rich changes in the functional repertoire associated with human brain function, which is impossible to explain through long-term plasticity. Neuromodulation evolved to allow for such flexibility by dynamically updating the effectivity of the fixed anatomical connectivity. Here, we introduce a theoretical framework modeling the dynamical mutual coupling between the neuronal and neurotransmitter systems. We demonstrate that this framework is crucial to advance our understanding of whole-brain dynamics by bidirectional coupling of the two systems through combining multimodal neuroimaging data (diffusion magnetic resonance imaging [dMRI], functional magnetic resonance imaging [fMRI], and positron electron tomography [PET]) to explain the functional effects of specific serotoninergic receptor (5-HT2AR) stimulation with psilocybin in healthy humans. This advance provides an understanding of why psilocybin is showing considerable promise as a therapeutic intervention for neuropsychiatric disorders including depression, anxiety, and addiction. Overall, these insights demonstrate that the whole-brain mutual coupling between the neuronal and the neurotransmission systems is essential for understanding the remarkable flexibility of human brain function despite having to rely on fixed anatomical connectivity.

 
Kringelbach, M. L., Cruzat, J., Cabral, J., Knudsen, G. M., Carhart-Harris, R., Whybrow, P. C., … & Deco, G. (2020). Dynamic coupling of whole-brain neuronal and neurotransmitter systems. Proceedings of the National Academy of Sciences, 117(17), 9566-9576., https://doi.org/10.1073/pnas.1921475117
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Trait Openness and serotonin 2A receptors in healthy volunteers: A positron emission tomography study.

January 11, 2019 / Mushrooms / Psilocybin, Papers, Personality, Psychology, Psychopharmacology, Publications / By / , , , , , ,

Abstract

Recent research found lasting increases in personality trait Openness in healthy individuals and patients after administration of the serotonin 2A receptor (5-HT2A R) agonist psilocybin. However, no studies have investigated whether 5-HT2A R availability as imaged using positron emission tomography (PET) is associated with this trait. In 159 healthy individuals (53 females), the association between 5-HT2A R binding in neocortex imaged with [18 F]altanserin or [11 C]Cimbi-36 PET and personality trait Openness was investigated using linear regression models. In these models the influence of sex on the association was also investigated. Trait Openness was assessed with the NEO Personality Inventory-Revised. No significant associations between neocortical 5-HT2A R binding and trait Openness were found for [18F]altanserin (p = 0.5) or [11 C]Cimbi-36 (p = 0.8). Pooling the data in a combined model did not substantially change our results (p = 0.4). No significant interactions with sex were found (p > 0.35). Our results indicate that differences in 5-HT2A R availability are not related to variations in trait Openness in healthy individuals. Although stimulation of the 5-HT2A R with compounds such as psilocybin may contribute to long-term changes in trait Openness, there is no evidence in favor of an association between 5-HT2A R and trait Openness.
Stenbæk, D. S., Kristiansen, S., Burmester, D., Madsen, M. K., Frokjaer, V. G., Knudsen, G. M., & Fisher, P. M. (2019). Trait Openness and serotonin 2A receptors in healthy volunteers: A positron emission tomography study. Human brain mapping., 10.1002/hbm.24511
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Whole-Brain Multimodal Neuroimaging Model Using Serotonin Receptor Maps Explains Non-linear Functional Effects of LSD

September 27, 2018 / Neuroscience, Other subjects, Other substances, Papers, Psychopharmacology, Psychotherapy, Publications / By / , , , , , ,

Abstract

Understanding the underlying mechanisms of the human brain in health and disease will require models with necessary and sufficient details to explain how function emerges from the underlying anatomy and is shaped by neuromodulation. Here, we provide such a detailed causal explanation using a whole-brain model integrating multimodal imaging in healthy human participants undergoing manipulation of the serotonin system. Specifically, we combined anatomical data from diffusion magnetic resonance imaging (dMRI) and functional magnetic resonance imaging (fMRI) with neurotransmitter data obtained with positron emission tomography (PET) of the detailed serotonin 2A receptor (5-HT2AR) density map. This allowed us to model the resting state (with and without concurrent music listening) and mechanistically explain the functional effects of 5-HT2AR stimulation with lysergic acid diethylamide (LSD) on healthy participants. The whole-brain model used a dynamical mean-field quantitative description of populations of excitatory and inhibitory neurons as well as the associated synaptic dynamics, where the neuronal gain function of the model is modulated by the 5-HT2AR density. The model identified the causative mechanisms for the non-linear interactions between the neuronal and neurotransmitter system, which are uniquely linked to (1) the underlying anatomical connectivity, (2) the modulation by the specific brainwide distribution of neurotransmitter receptor density, and (3) the non-linear interactions between the two. Taking neuromodulatory activity into account when modeling global brain dynamics will lead to novel insights into human brain function in health and disease and opens exciting possibilities for drug discovery and design in neuropsychiatric disorders.

Deco, G., Cruzat, J., Cabral, J., Knudsen, G. M., Carhart-Harris, R. L., Whybrow, P. C., … & Kringelbach, M. L. (2018). Whole-brain multimodal neuroimaging model using serotonin receptor maps explains non-linear functional effects of LSD. Current biology, 28(19), 3065-3074., 10.1016/j.cub.2018.07.083

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Classics in Neuroimaging: The Serotonergic 2A Receptor System-from Discovery to Modern Molecular Imaging

May 15, 2018 / LSD, Neuroscience, Other subjects, Papers, Psychopharmacology, Publications / By / , , , , ,

Abstract

Already in 1953, Woolley and Shaw speculated that serotonin could be involved in a range of central nervous system (CNS) disorders. Lysergic acid diethylamide (LSD) displayed an important role in this respect. It was used not only to antagonize biological effects of serotonin and to study the system itself, but also to identify serotonergic subtype receptors. The 5-HT2A receptor was discovered in the 1970s and identified as the responsible receptor mediating psychedelic effects of LSD. The development of positron emission tomography (PET) allowed to study this receptor system in vivo. Parameters such as abundance of 5-HT2A neuroreceptors or receptor occupancy can be determined using PET. As such, the development of 5-HT2A receptor tracers started immediately after the introduction of PET in the mid-1970s. In this Viewpoint, we provide a historical overview from the discovery of serotonin to the identification of the 5-HT2A receptor subtype and the subsequent development of 5-HT2A receptor subtype specific PET tracers over the last four decades. We emphasize the interplay between pharmacology, medicinal chemistry, radiochemistry, and nuclear medicine that is important while developing a PET tracer. Moreover, we highlight selected examples applying 5-HT2A receptor PET tracers within neurological diseases and drug occupancy studies.
T. L’Estrade, E., Hansen, H. D., Erlandsson, M., Ohlsson, T. G., Knudsen, G. M., & Herth, M. M. (2018). Classics in Neuroimaging: The Serotonergic 2A Receptor System—from Discovery to Modern Molecular Imaging. 10.1021/acschemneuro.8b00176
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In Vivo Imaging of Cerebral Serotonin Transporter and Serotonin 2A Receptor Binding in MDMA and Hallucinogen Users

June 6, 2011 / Ayahuasca, Cacti / Mescaline, DMT, LSD, MDMA, Mushrooms / Psilocybin, Neuroscience, Other subjects, Papers, Psychology, Psychopharmacology, Publications, Salvia / Salvinorin A / By / , , , , , ,

Abstract

Context:
Both hallucinogens and 3,4-methylenedioxy-methamphetamine (MDMA or “ecstasy”) have direct agonistic effects on postsynaptic serotonin 2A receptors, the key site for hallucinogenic actions. In addition, MDMA is a potent releaser and reuptake inhibitor of presynaptic serotonin.

Objective:
To assess the differential effects of MDMA and hallucinogen use on cerebral serotonin transporter (SERT) and serotonin2Areceptor binding.

Design:
A positron emission tomography study of 24 young adult drug users and 21 nonusing control partici-pants performed with carbon 11 (11C)–labeled 3-amino-4-[2-[(di(methyl)amino)methyl]phenyl]sulfanylbenzo-nitrile (DASB) and fluorine 18 (18F)–labeled altanserin, respectively. Scans were performed in the user group after a minimum drug abstinence period of 11 days, and the group was subdivided into hallucinogen-preferring users (n = 10) and MDMA-preferring users (n = 14).

Participants:
Twenty-four young adult users of MDMA and/or hallucinogenic drugs and 21 nonusing controls.

Main Outcome Measures:
In vivo cerebral SERT and serotonin 2A receptor binding.

Results:
Compared with nonusers, MDMA-preferring users showed significant decreases in SERT nondisplaceable binding potential (neocortex, −56%; pallidostriatum, −19%; and amygdala, −32%); no significant changes were seen in hallucinogen-preferring users. Both cortical and pallidostriatal SERT nondisplaceable binding potential was negatively correlated with the number of life-time MDMA exposures, and the time of abstinence from MDMA was positively correlated with subcortical, but not cortical, SERT binding. A small decrease in neocortical serotonin 2A receptor binding in the serotonin 2A receptor agonist users (both user groups) was also detected.

Conclusions
We found evidence that MDMA but not hallucinogen use is associated with changes in the cerebral presynaptic serotonergic transmitter system. Because hallucinogenic drugs primarily have serotonin 2A receptor agonistic actions, we conclude that the negative association between MDMA use and cerebral SERT binding is mediated through a direct presynaptic MDMA effect rather than by the serotonin 2A agonistic effects of MDMA. Our cross-sectional data suggest that subcortical, but not cortical, recovery of SERT binding might take place after several months of MDMA abstinence.

Erritzoe, D., Frokjaer, V. G., Holst, K. K., Christoffersen, M., Johansen, S. S., Svarer, C., … Knudsen, G. M. (2011). In Vivo Imaging of Cerebral Serotonin Transporter and Serotonin 2A Receptor Binding in 3,4-Methylenedioxymethamphetamine (MDMA or “Ecstasy”) and Hallucinogen Users. Archives of General Psychiatry, 68(6), 562-576. http://dx.doi.org/10.1001/archgenpsychiatry.2011.56
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30 April - Q&A with Rick Strassman

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