The serotonergic hallucinogen 5-methoxy-N,N-dimethyltryptamine disrupts cortical activity in a regionally-selective manner via 5-HT1A and 5-HT2A receptors

This rodent study investigates the response to 5-MeO-DMT on cortical activity via genetic knockout of the serotonin 5-HT2A receptor in their test mice and the selective inhibition of 5-HT_1A receptors via antipsychotic drugs. 5-MeO-DMT evoked marked alterations in the function of primary sensory areas (Au1, S1, V1) as well as in the highest association cortex (PFC), with a differential contribution of the 5-HT1A and 5-HT2A receptors that were selectively inhibited by antipsychotic drugs.

Abstract

“Introduction: 5-Methoxy-N,N-dimethyltryptamine (5-MeO-DMT) is a natural hallucinogen, acting as a non-selective serotonin 5-HT_1A/5-HT_2A-R agonist. Psychotomimetic agents such as the non-competitive NMDA-R antagonist phencyclidine and serotonergic hallucinogens (DOI and 5-MeO-DMT) disrupt cortical synchrony in the low frequency range (<4 Hz) in rat prefrontal cortex (PFC), an effect reversed by antipsychotic drugs.

Methods: Here we extend these observations by examining the effect of 5-MeO-DMT on low frequency cortical oscillations (LFCO, <4 Hz) in PFC, visual (V1), somatosensory (S1) and auditory (Au1) cortices, as well as the dependence of these effects on 5-HT_1A-R and 5-HT_2A-R, using wild type (WT) and 5-HT_2A-R knockout (KO2A) anesthetized mice.

Results: 5-MeO-DMT reduced LFCO in the PFC of WT and KO2A mice. The effect in KO2A mice was fully prevented by the 5-HT_1A-R antagonist WAY-100635. Systemic and local 5-MeO-DMT reduced 5-HT release in PFC mainly via 5-HT_1A-R. Moreover, 5-MeO-DMT reduced LFCO in S1, Au1 and V1 of WT mice and only in V1 of KO2A mice, suggesting the involvement of 5-HT_1A-R activation in the 5-MeO-DMT-induced disruption of V1 activity. In addition, antipsychotic drugs reversed 5-MeO-DMT effects in WT mice.

Discussion: The present results suggest that the hallucinogen action of 5-MeO-DMT is mediated by simultaneous alterations of the activity of sensory (S1, Au1, V1) and associative (PFC) cortical areas, also supporting a role of 5-HT_1A-R stimulation in V1 and PFC, in addition to the well-known action on 5-HT_2A-R. Moreover, the reversal by antipsychotic drugs of 5-MeO-DMT effects adds to previous literature supporting the usefulness of the present model in antipsychotic drug development.”

Authors: Maurizio S. Riga,  Analia Bortolozzi, Letizia Campa, Francesc Artigas & Pau Celada

Summary

Pau Celada, PhD, performed an in vitro study on the effects of 5-meO-DMT on the prefrontal cortex, sensorial cortical areas, visual cortex, 5-HT receptors, oscillatory activity.

5-MeO-DMT is a natural hallucinogen that acts as a non-selective serotonin 5-HT 1A /5-HT 2A -R agonist. It disrupts cortical synchrony in the low frequency range (4 Hz) in the rat prefrontal cortex. 5-MeO-DMT reduced LFCO in the PFC of WT and KO2A mice, and also in S1, Au1 and V1 of WT mice. Antipsychotic drugs reversed 5-MeO-DMT effects in WT mice, supporting a role for 5-HT 1A -R stimulation in V1 and PFC.

Serotoninergic hallucinogens are divided into two main classes: indoleamines and phenylalkylamines. These agents evoke profound changes in perception, thought, mood and cognition and are used to study brain areas/circuits altered in psychiatric disorders. 5-MeO-DMT is a potent fast-acting hallucinogen that induces various physiological and behavioral changes in animal models. It is currently controlled as a Schedule I hallucinogen by the Drug Enforcement Administration. The psychotomimetic action of classical hallucinogens is mainly mediated by their agonistic actions at cortical 5-HT 2A -R, although 5-HT 1A -R may also play an important role in the behavioral effects of indoleamine hallucinogens as well as in the mechanism of action of antipsychotic drugs.

Previous studies showed that psychotropic agents with different mechanism of action, such as phencyclidine (PCP), DOI and 5-MeO-DMT, disrupted the activity of rodent prefrontal cortex (PFC), increasing pyramidal neuron discharge and reducing low frequency cortical oscillations (LFCO, 4Hz). Classical and atypical antipsychotic drugs reversed these alterations in all cases.

5-MeO-DMT, risperidone, WAY-100635 maleate, haloperidol and citalopram hydrobromide were dissolved in saline and injected subcutaneously. Local effects were assessed in mPFC using artificial cerebrospinal fluid.

2.3. Electrophysiology

Mice were anesthetized with chloral hydrate and recorded in the medial PFC. After 5 min, drugs were administered, and KO2A mice were pretreated with saline or the selective 5-HT 1A -R WAY-100635 to test the role of the 5-HT 1A -R on 5-MeO-DMT induced disruption of prefrontal activity. Intracerebral microdialysis was performed to measure extracellular serotonin (5-HT) concentrations in freely moving mice 20-24 h after surgery. Head twitching was scored for 4 consecutive 5-min periods by direct observation of mice undergoing in vivo microdialysis, in basal conditions and after 5-MeO-DMT administration. Data and statistical analysis were performed using the Spike2 software. The power spectrum of 3 minutes signal was analyzed off-line.

Data were collected on a computer line using Spike2 software built-in and self-developed routines, and analyzed by Student’s t-test or two-way repeated-measures analysis of variance (ANOVA), with treatment (or area) and genotype as factors, followed by Newman – Keuls post-hoc test, as appropriate.

LFCO power spectra in mouse mPFC, S1, Au1 and V1 were similar among genotypes (WT: 0.0540.004, KO2A: 0.0640.004 v 2; n.s Student’s t-test; n=40 and 22, respectively).

3.2. Effect of 5-MeO-DMT on LFCO in mPFC of WT and KO2A mice

5-MeO-DMT reduced LFCO in the mPFC of WT and KO2A mice differently, with no significant treatment x genotype interaction.

Figure 1 shows that subcutaneous administration of 5-MeO-DMT decreased low frequency cortical oscillations in mPFC of WT and KO2A mice. The effects of 5-MeO-DMT were similar in WT and KO2A mice, but were greater in KO2A mice.

We administered 5-MeO-DMT subcutaneously to WT and KO2A mice, and measured LFCO 12 and 24 min post-administration. 5-MeO-DMT reduced LFCO in the mPFC of WT and KO2A mice, and the effect was different at different post-administration times.

The 5-HT 1A receptor antagonist WAY-100635 prevented the 5-MeO-DMT-evoked reduction of LFCO in the mPFC of KO2A mice, and increased the power of LFCO by itself.

WAY-100635, a 5-HT 1A receptor antagonist, prevents the 5-MeO-DMT effect on low frequency cortical oscillations in KO2A mice. The effect of 5-MeO-DMT on LFCO was only observed in KO2A mice pretreated with saline.

A systemic administration of 5-MeO-DMT decreased extracellular 5-HT concentration comparably in the mPFC of WT and KO2A mice. The administration of 5-MeO-DMT produced a significant increase in the spontaneous HTR rate in WT but not in KO2A mice.

5-MeO-DMT administration decreased 5-HT extracellular concentration and increased HTR in WT but not in KO2A mice. Local application of 5-MeO-DMT by reverse dialysis increased 5-HT extracellular concentration in WT mice but decreased 5-HT extracellular concentration in KO2A mice. We locally applied 5-MeO-DMT in the mPFC of WT and KO2A mice by reverse dialysis to discriminate the involvement of presynaptic and postsynaptic 5-HT 1A -R in the reduction of 5-HT release induced by 5-MeO-DMT.

5-MeO-DMT significantly increased extracellular 5-HT in WT mice but decreased extracellular 5-HT in KO2A mice. The higher the concentration, the greater the difference in extracellular 5-HT between WT and KO2A mice.

We examined the effect of 5-MeO-DMT on LFCO in WT mice and found that the antipsychotic drugs haloperidol and risperidone could reverse the disruption alteration of mPFC activity induced by 5-MeO-DMT.

Figure 4 shows that 5-MeO-DMT (1 mg/kg subcutaneously) has an effect on low frequency cortical oscillations (LFCO) and that haloperidol and risperidone reverse this effect.

We recorded LFCO in S1, Au1 and V1 using ECoGs to examine whether sensory cortical are affected by 5-MeO-DMT. 5-MeO-DMT reduced LFCO in S1, Au1 and V1 of WT mice, but not in S1 and Au1 of KO2A mice.

Figure 5 shows that 5-MeO-DMT has a similar effect on the low frequency cortical oscillations (LFCO) in the primary somatosensory (S1) primary auditory (Au1) and primary visual (V1) cortices of WT and KO2A mice, but a different effect on the LFCO in V1 of KO2A mice.

The present study confirms and extends previous observations in rat brain, showing that 5-MeO-DMT decreases LFCO in PFC by stimulating 5-HT 1A -R and 5-HT 2A -R, and that this effect is reversed by classical and atypical antipsychotic drugs. In recent years, we have found that the action of psychotomimetic agents, including PCP and serotonergic hallucinogens, is mediated by the activation of 5-HT 2A -R, but also by 5-HT 1A -R. 5-HeO-DMT reduced LFCO and the BOLD signal in PFC and V1 of the rat, and reduced LFCO in the PFC of WT mice, as previously observed in rats. The reduction was prevented or reversed by selective 5-HT 1A -R and 5-HT 2A -R antagonists.

In KO2A mice, WAY-100635 enhanced LFCO evoked by 5-MeO-DMT but not in WT mice. This difference may be due to a compensatory change in the control of LFCO by 5-HT 1A -R. 5-MeO-DMT reduced the discharge of 5-HT neurons in the mPFC, and this effect might be due to the activation of 5-HT 1A -R and 5-HT 2A -R in pyramidal neurons projecting to the DR. We examined the relative contribution of pre- and postsynaptic 5-HT 1A -R in 5-HT release in PFC after systemic and local application of 5-MeO-DMT. We found that presynaptic 5-HT 1A -R was predominant in 5-HT release reduction in WT mice after systemic 5-MeO-DMT administration. The results suggest that 5-MeO-DMT acts preferentially on 5-HT 1A -R at low doses, occupying both receptors at higher doses. However, the effects of 5-MeO-DMT are countered by antipsychotic drugs.

Haloperidol may restore the excitatory/inhibitory balance altered by 5-MeO-DMT in the mPFC, by acting via different signalling pathways and/or cortical networks. 5-MeO-DMT reduced LFCO in S1, Au1 and V1 of WT mice, but only in V1 of KO2A mice. This suggests a preferential involvement of 5-HT1A -R in V1. 5-HT 1A -R and 5-HT 2A -R are densely expressed in V1 of the human primary visual cortex and are involved in the modulation of thalamic visual inputs from the lateral geniculate nucleus. These receptors are also involved in the sensory alterations evoked by psilocybin and 5-MeO-DMT. The activation of excitatory (5-HT 2A -R) and inhibitory (5-HT 1A -R) receptors contribute to reduce LFCO in the PFC, but the effects may depend on the proportion of 5-HT 2A -R and 5-H1A -R in pyramidal and GABAergic neurons in the different cortical areas examined.

5. Conclusions

The indoleamine hallucinogen 5-MeO-DMT induces marked alterations in the function of primary sensory areas as well as in the highest association cortex, which are mediated by 5-HT1A-Rs and 5-HT2A-Rs.

Funding and disclosure

This work was supported by grants from the Instituto de Salud Carlos III, SAF 2012-35183, CIBERSAM P82, 11INT3, and the Innovative Medicines Initiative Joint Undertaking (IMI) and the Generalitat de Catalunya. F.A. is PI of two grants from Lundbeck.