Shared and Distinct Brain Regions Targeted for Immediate Early Gene Expression by Ketamine and Psilocybin

Abstract

Psilocybin is a psychedelic with therapeutic potential. While there is growing evidence that psilocybin exerts its beneficial effects through enhancing neural plasticity, the exact brain regions involved are not completely understood. Determining the impact of psilocybin on plasticity-related gene expression throughout the brain can broaden our understanding of the neural circuits involved in psychedelic-evoked neural plasticity. In this study, whole-brain serial two-photon microscopy and light sheet microscopy were employed to map the expression of the immediate early gene, c-Fos, in male and female mice. The drug-induced c-Fos expression following psilocybin administration was compared to that of subanesthetic ketamine and saline control. Psilocybin and ketamine produced acutely comparable elevations in c-Fos expression in numerous brain regions, including anterior cingulate cortex, locus coeruleus, primary visual cortex, central and basolateral amygdala, medial and lateral habenula, and claustrum. Select regions exhibited drug-preferential differences, such as dorsal raphe and insular cortex for psilocybin and the CA1 subfield of hippocampus for ketamine. To gain insights into the contributions of receptors and cell types, the c-Fos expression maps were related to brain-wide in situ hybridization data. The transcript analyses showed that the endogenous levels of Grin2a and Grin2b predict whether a cortical region is sensitive to drug-evoked neural plasticity for both ketamine and psilocybin. Collectively, the systematic mapping approach produced an unbiased list of brain regions impacted by psilocybin and ketamine. The data are a resource that highlights previously underappreciated regions for future investigations. Furthermore, the robust relationships between drug-evoked c-Fos expression and endogenous transcript distributions suggest glutamatergic receptors as a potential convergent target for how psilocybin and ketamine produce their rapid-acting and long-lasting therapeutic effects.

UNRAVELing the synergistic effects of psilocybin and environment on brain-wide immediate early gene expression in mice

“…Our findings generally agree with a recent regional analysis of psilocybin-mediated c-Fos expression across the mouse brain using LSFM and two-photon microscopy (Davoudian et al, 2023). However, our higher resolution voxel-wise analysis technique resolved focal changes in neural activity among more sizeable structures that may have modest or no changes in activity when considered as a whole.…”

“…We posed this question in a more tractable mouse model using a broad environmental manipulation (home cage versus enriched environment) that does not assume which mouse behavioral outcomes are therapeutically relevant, and with a psilocybin dose (2 mg/kg, i.p.) that falls within the range widely used across mouse studies (Davoudian et al, 2023; Fadahunsi et al, 2022; Golden & Chadderton, 2022; Hesselgrave et al, 2021; Shao et al, 2021).…”

“…To study the effect of environmental context on psychedelic-elicited states in mice, we mapped, at cellular resolution, neural activities related to context, psilocybin, and the interaction between these factors. To capture experience-dependent brain activity, we performed immunofluorescent labeling of c-Fos, an immediate early gene (IEG) product and transcription factor that is transiently expressed after neural activation (Sagar et al, 1988), followed by brain clearing via iDISCO+ (Renier et al, 2016) and light sheet fluorescent microscopy (LSFM) (Davoudian et al, 2023; Hansen et al, 2021; Jin et al, 2022; Renier et al, 2016). Psilocybin or saline was administered to mice in two distinct contexts, a familiar home cage or an enriched environment (EE) known to promote neural and behavioral plasticity (Nithianantharajah & Hannan, 2006).…”

Acute psilocybin enhances cognitive flexibility in rats

“…At the level of neuronal networks, psilocybin may impact set-shifting by modulating neuronal activity in mPFC both directly, via activation of 5HT receptors, as well as indirectly via its effects on neuromodulatory regions that project to frontal cortex. Recent results that show a preeminent role of inhibitory interneurons in mediating strategy switching [55,56] and increased expression of activity-dependent genes in inhibitory neurons in the mPFC following psilocybin administration [57] support this notion. Psilocybin also impacts the activity in the dorsal raphe nucleus (DRN) and the locus coeruleus (LC) [58–62].…”

Whole-brain tracking of cocaine and sugar rewards processing

“…The whole-brain mapping of the neuronal activity after drugs exposure Brain clearing combined with IEGs labeling and light-sheet imaging offers unbiased, single-cell resolution analysis of the task-dependent neuronal activity in rodents. This approach has already served to characterize c-Fos expression elicited by drugs: medications regulating appetite, antipsychotics (haloperidol), and psychedelics (ketamine and psilocybin) [16,42,43]. c-Fos was also mapped in the brains of mice withdrawn from alcohol, psychostimulants, or opioids [12,13,21,11].…”