5-HT2A receptors shape whole-brain monoaminergic coherence in male mice.

Serotonergic psychedelics disrupt the normally organized pattern of correlations among serotonin, dopamine, and noradrenaline concentrations across 28 brain regions in mice during forced exploratory behavior. Both the 5-HT2A receptor agonist TCB-2 and the antagonist MDL-100,907 decreased correlations between regional neurochemical levels, while combining them partially restored those correlations. TCB-2 dose-dependently reduced serotonin turnover across all brain regions and dopamine turnover in the striatum, and enhanced markers of dopamine and noradrenaline systems in the anterior cingulate cortex. MDL-100,907 alone had minimal effects on monoamine levels but reduced TCB-2-induced head twitches and increased monoamine concentrations in the anterior cingulate cortex without affecting the serotonin turnover decrease. The functional connectivity of monoaminergic systems during exploration is highly sensitive to modulation through 5-HT2A receptor activation or blockade.

Study at a glance

Abstract

The mechanism of action of serotonergic psychedelics is increasingly explored worldwide due to their clinical benefits in various psychiatric conditions. Beyond the stimulation of serotonin 2 A (5-HT2A) receptors, psychedelics may desynchronize activity between brain regions, however the involvement of corresponding neurotransmission systems has been largely overlooked. Given that monoaminergic systems target virtually all brain regions and play a role in exploratory behavior, we hypothesized that psychedelics disrupt the coherence of monoamine systems across brain regions during forced exploratory behavior in mice. Using post-mortem tissue quantification of serotonin (5-HT), dopamine (DA), noradrenaline (NA), and their metabolites in 28 distinct brain regions, we observed a dense and highly organized pattern of correlations within and between monoamines in vehicle-treated mice. This organization was disrupted by both the psychedelic 5-HT2A receptor agonist TCB-2 (0.3, 3 and 10 mg/kg) and the antagonist MDL-100,907 (0.2 mg/kg), both of which decreased correlations between regional neurochemical concentrations. Interestingly, the combination of MDL-100,907 and TCB-2 partially restored correlations. Quantitatively, TCB-2 dose-dependently decreased 5-HT turnover (metabolite/5-HT) across all brain regions, and DA turnover (3-methoxytyramine/DA) in the striatum. TCB-2 also enhanced markers of the DA and NA systems in certain brain regions, notably including the anterior cingulate cortex. MDL-100,907, which had minimal impact on monoamine levels when administered alone, reduced TCB-2 (3 mg/kg)-induced head twitches and increased monoamine concentrations in the anterior cingulate cortex, but did not affect the TCB-2-induced decrease 5-HT turnover across the brain. These data suggest that the functional connectivity of monoaminergic systems during exploration is highly sensitive to modulation through either activation or blockade of 5-HT2A receptors.