A pilot study of cerebral metabolism and serotonin 5-HT2A receptor occupancy in rats treated with the psychedelic tryptamine DMT in conjunction with the MAO inhibitor harmine

Rationale: The psychedelic effects of the traditional Amazonian botanical decoction known as ayahuasca are often attributed to agonism at brain serotonin 5-HT2A receptors by N,N-dimethyltryptamine (DMT). To reduce first pass metabolism of oral DMT, ayahuasca preparations additionally contain reversible monoamine oxidase A (MAO-A) inhibitors, namely β-carboline alkaloids such as harmine. However, there is lacking biochemical evidence to substantiate this pharmacokinetic potentiation of DMT in brain via systemic MAO-A inhibition.Objectives: We measured the pharmacokinetic profile of harmine and/or DMT in rat brain, and tested for pharmacodynamic effects on brain glucose metabolism and DMT occupancy at brain serotonin 5-HT2A receptors.Methods: We first measured brain concentrations of harmine and DMT after treatment with harmine and/or DMT at low sub-cutaneous doses (1 mg/kg each) or harmine plus DMT at moderate doses (3 mg/kg each). In the same groups of rats, we also measured ex vivo the effects of these treatments on the availability of serotonin 5-HT2A receptors in frontal cortex. Finally, we explored effects of DMT and/or harmine (1 mg/kg each) on brain glucose metabolism with [18F]FDG-PET.Results: Results confirmed that co-administration of harmine inhibited the formation of the DMT metabolite indole-3-acetic acid (3-IAA) in brain, while correspondingly increasing the cerebral availability of DMT. However, we were unable to detect any significant occupancy by DMT at 5-HT2A receptors measured ex vivo, despite brain DMT concentrations as high as 11.3 µM. We did not observe significant effects of low dose DMT and/or harmine on cerebral [18F]FDG-PET uptake.Conclusion: These preliminary results call for further experiments to establish the dose-dependent effects of harmine/DMT on serotonin receptor occupancy and cerebral metabolism

A single dose of psilocybin induces lasting changes in metabolic connectivity within biologically informed rat brain networks related to compulsions and anxiety.

Pharmacotherapy with psilocybin, a serotonergic psychedelic, shows promising benefits in a range of neuropsychiatric disorders. While its psychedelic effects last for a few hours, therapeutic effects of psilocybin can persist long after a single administration in clinical and preclinical studies. We tested the hypothesis that these therapeutic effects entail remodeling of biologically informed rat brain networks related to compulsions and anxiety. Specifically, the cortico-striato-thalamo-cortical (CSTC) network and the cortico-amygdalo-hippocampal-hypothalamus (CAHH) networks. We used serial positron emission tomography (PET) to assess the acute and persistent effects of a single psilocybin dose on glucose metabolism and metabolic connectivity in the CSTC and CAHH networks in rat brain, in relation to the in vivo occupancy at serotonin 5HT2A receptors after acute psilocybin challenge. Notably, we found metabolic changes in two of the main hubs in the CSTC network i.e. thalamus and dorsal striatum accompanied by a persistent change in metabolic connectivity between thalamus and medial prefrontal cortex which may indicate a shift in thalamocortical gating after acute administration of psilocybin. Within the CAHH network, we found an acute metabolic increase in insula after psilocybin administration and a persistent enhancement of metabolic connectivity between the insula and the medial prefrontal cortex, and the ventral hippocampus. Our findings of acute and persistent changes in metabolic activity and connectivity within these networks provide new insights towards understanding the mechanism of the therapeutic effects of psilocybin in a range of neuropsychiatric disorders

Pharmacokinetic and Pharmacodynamic Interaction of the Ayahuasca Constituents Harmine and Dimethyltryptamine (DMT) in the Rat Brain

Rationale The psychedelic effects of the traditional Amazonian botanical decoction known as ayahuasca are attributed to the effects of N,N-dimethyltryptamine (DMT) at brain serotonin 5-HT2A receptors. To make oral DMT bioavailable, ayahuasca additionally contains reversible monoamine oxidase A (MAO-A) inhibitors, namely β-carboline alkaloids such as harmine. However, there is lacking biochemical evidence to substantiate this pharmacokinetic potentiation in the brain. Objectives Therefore, we measured the pharmacokinetic profile of harmine and DMT in the rat brain. Additionally, we investigated the pharmacodynamic properties of DMT and/or harmine. Methods We first measured brain concentrations of harmine and DMT after treatment with harmine and/or DMT at low doses (1 mg/kg each) or harmine plus DMT at moderate doses (3 mg/kg each). In the same groups of rats, we also measured ex vivo the effects of these treatments on the availability of serotonin 5-HT2A receptors in frontal cortex. Finally, we explored influences of DMT and/or harmine in the lower dose group on brain glucose metabolism with [18F]FDG-PET. Results Results confirmed that co-administration of harmine inhibited the formation of the DMT metabolite indole-3-acetic acid (3-IAA) in the brain, while increasing the cerebral availability of DMT. However, we were unable to detect any significant occupancy by DMT at 5-HT2A receptors measured ex vivo, despite brain DMT concentrations as high as 11.3 µM at moderate doses. We did not observe strong influences of low dose DMT and/or harmine on [18F]FDG-PET. Conclusions The present preliminary results call for further experiments to establish the dose-dependent effects of harmine/DMT on receptor occupancy and on cerebral metabolism

A pilot study of cerebral metabolism and serotonin 5-HT2A receptor occupancy in rats treated with the psychedelic tryptamine DMT in conjunction with the MAO inhibitor harmine

Rationale: The psychedelic effects of the traditional Amazonian botanical decoction known as ayahuasca are often attributed to agonism at brain serotonin 5-HT2A receptors by N,N-dimethyltryptamine (DMT). To reduce first pass metabolism of oral DMT, ayahuasca preparations additionally contain reversible monoamine oxidase A (MAO-A) inhibitors, namely beta-carboline alkaloids such as harmine. However, there is lacking biochemical evidence to substantiate this pharmacokinetic potentiation of DMT in brain via systemic MAO-A inhibition.Objectives: We measured the pharmacokinetic profile of harmine and/or DMT in rat brain, and tested for pharmacodynamic effects on brain glucose metabolism and DMT occupancy at brain serotonin 5-HT2A receptors.Methods: We first measured brain concentrations of harmine and DMT after treatment with harmine and/or DMT at low sub-cutaneous doses (1 mg/kg each) or harmine plus DMT at moderate doses (3 mg/kg each). In the same groups of rats, we also measured ex vivo the effects of these treatments on the availability of serotonin 5-HT2A receptors in frontal cortex. Finally, we explored effects of DMT and/or harmine (1 mg/kg each) on brain glucose metabolism with [F-18]FDG-PET.Results: Results confirmed that co-administration of harmine inhibited the formation of the DMT metabolite indole-3-acetic acid (3-IAA) in brain, while correspondingly increasing the cerebral availability of DMT. However, we were unable to detect any significant occupancy by DMT at 5-HT2A receptors measured ex vivo, despite brain DMT concentrations as high as 11.3 mu M. We did not observe significant effects of low dose DMT and/or harmine on cerebral [F-18]FDG-PET uptake.Conclusion: These preliminary results call for further experiments to establish the dose-dependent effects of harmine/DMT on serotonin receptor occupancy and cerebral metabolism.ISSN:1663-981

Synaptic Density and Neuronal Metabolic Function Measured by Positron Emission Tomography in the Unilateral 6-OHDA Rat Model of Parkinson’s Disease

Parkinson’s disease (PD) is caused by progressive neurodegeneration and characterised by motor dysfunction. Neurodegeneration of dopaminergic neurons also causes aberrations within the cortico-striato-thalamo-cortical (CSTC) circuit, which has been hypothesised to lead to non-motor symptoms such as depression. Individuals with PD have both lower synaptic density and changes in neuronal metabolic function in the basal ganglia, as measured using [(11)C]UCB-J and [(18)F]FDG positron emission tomography (PET), respectively. However, the two radioligands have not been directly compared in the same PD subject or in neurodegeneration animal models. Here, we investigate [(11)C]UCB-J binding and [(18)F]FDG uptake in the CSTC circuit following a unilateral dopaminergic lesion in rats and compare it to sham lesioned rats. Rats received either a unilateral injection of 6-hydroxydopamine (6-OHDA) or saline in the medial forebrain bundle and rostral substantia nigra (n = 4/group). After 3 weeks, all rats underwent two PET scans using [(18)F]FDG, followed by [(11)C]UCB-J on a separate day. [(18)F]FDG uptake and [(11)C]UCB-J binding were both lower in the ipsilateral striatal regions compared to the contralateral regions. Using [(11)C]UCB-J, we could detect an 8.7% decrease in the ipsilateral ventral midbrain, compared to a 2.9% decrease in ventral midbrain using [(18)F]FDG. Differential changes between hemispheres for [(11)C]UCB-J and [(18)F]FDG outcomes were also evident in the CSTC circuit’s cortical regions, especially in the orbitofrontal cortex and medial prefrontal cortex where higher synaptic density yet lower neuronal metabolic function was observed, following lesioning. In conclusion, [(11)C]UCB-J and [(18)F]FDG PET can detect divergent changes following a dopaminergic lesion in rats, especially in cortical regions that are not directly affected by the neurotoxin. These results suggest that combined [(11)C]UCB-J and [(18)F]FDG scans could yield a better picture of the heterogeneous cerebral changes in neurodegenerative disorders

Dorsal striatal dopamine induces fronto-cortical hypoactivity and attenuates anxiety and compulsive behaviors in rats.

Dorsal striatal dopamine transmission engages the cortico-striato-thalamo-cortical (CSTC) circuit, which is implicated in many neuropsychiatric diseases, including obsessive-compulsive disorder (OCD). Yet it is unknown if dorsal striatal dopamine hyperactivity is the cause or consequence of changes elsewhere in the CSTC circuit. Classical pharmacological and neurotoxic manipulations of the CSTC and other brain circuits suffer from various drawbacks related to off-target effects and adaptive changes. Chemogenetics, on the other hand, enables a highly selective targeting of specific neuronal populations within a given circuit. In this study, we developed a chemogenetic method for selective activation of dopamine neurons in the substantia nigra, which innervates the dorsal striatum in the rat. We used this model to investigate effects of targeted dopamine activation on CSTC circuit function, especially in fronto-cortical regions. We found that chemogenetic activation of these neurons increased movement (as expected with increased dopamine release), rearings and time spent in center, while also lower self-grooming. Furthermore, this activation increased prepulse inhibition of the startle response in females. Remarkably, we observed reduced [18F]FDG metabolism in the frontal cortex, following dopamine activation in the dorsal striatum, while total glutamate levels- in this region were increased. This result is in accord with clinical studies of increased [18F]FDG metabolism and lower glutamate levels in similar regions of the brain of people with OCD. Taken together, the present chemogenetic model adds a mechanistic basis with behavioral and translational relevance to prior clinical neuroimaging studies showing deficits in fronto-cortical glucose metabolism across a variety of clinical populations (e.g. addiction, risky decision-making, compulsivity or obesity)

DataSheet1_A pilot study of cerebral metabolism and serotonin 5-HT2A receptor occupancy in rats treated with the psychedelic tryptamine DMT in conjunction with the MAO inhibitor harmine.pdf

Rationale: The psychedelic effects of the traditional Amazonian botanical decoction known as ayahuasca are often attributed to agonism at brain serotonin 5-HT2A receptors by N,N-dimethyltryptamine (DMT). To reduce first pass metabolism of oral DMT, ayahuasca preparations additionally contain reversible monoamine oxidase A (MAO-A) inhibitors, namely β-carboline alkaloids such as harmine. However, there is lacking biochemical evidence to substantiate this pharmacokinetic potentiation of DMT in brain via systemic MAO-A inhibition.Objectives: We measured the pharmacokinetic profile of harmine and/or DMT in rat brain, and tested for pharmacodynamic effects on brain glucose metabolism and DMT occupancy at brain serotonin 5-HT2A receptors.Methods: We first measured brain concentrations of harmine and DMT after treatment with harmine and/or DMT at low sub-cutaneous doses (1 mg/kg each) or harmine plus DMT at moderate doses (3 mg/kg each). In the same groups of rats, we also measured ex vivo the effects of these treatments on the availability of serotonin 5-HT2A receptors in frontal cortex. Finally, we explored effects of DMT and/or harmine (1 mg/kg each) on brain glucose metabolism with [18F]FDG-PET.Results: Results confirmed that co-administration of harmine inhibited the formation of the DMT metabolite indole-3-acetic acid (3-IAA) in brain, while correspondingly increasing the cerebral availability of DMT. However, we were unable to detect any significant occupancy by DMT at 5-HT2A receptors measured ex vivo, despite brain DMT concentrations as high as 11.3 µM. We did not observe significant effects of low dose DMT and/or harmine on cerebral [18F]FDG-PET uptake.Conclusion: These preliminary results call for further experiments to establish the dose-dependent effects of harmine/DMT on serotonin receptor occupancy and cerebral metabolism.</p