An analog of psychedelics restores functional neural circuits disrupted by unpredictable stress

Stress triggers adaptive allostatic responses, but prolonged or chronic stress can overwhelm these mechanisms and predispose individuals to mental illnesses. Rodent studies show region-specific synaptic and circuit alterations after chronic stress, including dendritic atrophy and spine loss in hippocampus, medial prefrontal cortex, and somatosensory cortex, with contrasting increases in spine density and dendritic branching in amygdala and orbitofrontal cortex. At the circuit level, stress disrupts excitation–inhibition balance, leading to behavioral abnormalities such as elevated anxiety, impaired sensory processing, and reduced cognitive flexibility. Psychedelics (e.g., LSD, psilocybin, DMT) have resurfaced as potential therapeutics for stress-related psychiatric disorders, but their hallucinogenic effects remain a major drawback. Tabernanthalog (TBG), an analog of 5-MeO-DMT, does not induce the head-twitch response in mice and has shown anti-addictive and antidepressant potential. The present study investigates whether a single post-stress dose of TBG can rescue UMS-induced deficits in anxiety-like behavior, sensory processing, and cognitive flexibility, and examines underlying cortical circuit mechanisms, including dendritic spine dynamics and neuronal activity modulation in somatosensory cortex.

Prior work demonstrates that chronic stress induces robust, region-specific structural remodeling: dendritic atrophy and spine loss in hippocampal CA1/CA3, medial prefrontal cortex, and somatosensory cortex, but increased spine density/branching in basolateral amygdala and orbitofrontal cortex. Stress perturbs excitation–inhibition balance and neural circuit function, correlating with behavioral changes such as heightened anxiety, impaired sensory processing, and reduced decision-making flexibility. Clinical and preclinical studies of classical psychedelics indicate therapeutic potential across OCD, anxiety, depression, and substance abuse, yet hallucinogenic liability limits their use. TBG, a non-hallucinogenic analog of 5-MeO-DMT, emerged as a candidate with antidepressant and anti-addictive properties, but its effects on stressed brain circuits were previously unknown.

• Experimental animals: Thy1-GFP-M and C57BL/6J mice (both sexes, 1–2 months) were group-housed on a 12 h light/dark cycle and randomly assigned to groups. Experiments followed approved IACUC protocols (UC Santa Cruz and Stanford).
• Unpredictable mild stress (UMS): 2-month-old mice underwent a 7-day UMS paradigm comprising varied mild stressors (per prior description and Supplementary Table 1).
• Elevated plus maze (EPM): Custom plexiglass EPM (arms 30 × 5 cm; closed arm walls 15 cm; elevated 50 cm). Each mouse explored for 5 min. Behavior tracked with Bonsai and DeepLabCut; custom Python/Matlab quantified distance traveled and time in open vs. closed arms.
• Four-choice odor discrimination and reversal: Custom 4-quadrant acrylic arena with ramekins delivering odor cues (rosemary, clove, thyme, nutmeg/cinnamon). Food reward: ~10 mg Honey Nut Cheerios pieces. Mice food-restricted to 80–85% baseline weight; handling and two-day pre-training (acclimation and digging shaping). On test day, mice learned initial odor-reward association (criterion: 8/10 consecutive correct), followed immediately by reversal with one novel odor (cinnamon) and same criterion. Omissions recorded if no choice within 3 min.
• Whisker-dependent texture discrimination (WTD): Free-moving assay in chamber (38 × 28 × 23 cm): habituation, encoding with two identical textures (e.g., 220 grit sandpaper), rest, and testing with one familiar and one novel texture (e.g., 60 grit). Exclusion for insufficient engagement or side bias. Head-fixed version in Neurotar mobile home cage: habituation to head-fixation, then free exploration, encoding with two identical textures, resting, and testing with familiar vs. novel textures; behavior recorded with IR camera and analyzed with BORIS. Discrimination index computed as (approaches to novel − approaches to familiar) / (approaches to both).
• Drug administration: TBG synthesized as described previously; TBG or fluoxetine HCl administered intraperitoneally at 10 mg/kg; 0.9% saline as vehicle.
• Cranial window implantation and virus injection: At ~P30, circular craniotomy (2.3 mm diameter) over S1 barrel field (AP −1.5 mm, ML 3.5 mm) or frontal cortex (AP +1.7 mm, ML 1.0 mm). For spine imaging, Thy1-GFP-M mice used. For L2/3 Ca imaging, C57BL/6J mice received AAV2/1-Syn-GCaMP6f injections (two sites, ~150 nL each, 150–200 µm depth). Window sealed with glass coverslip and annular ‘doughnut’; headplate affixed. Perioperative medications: dexamethasone, carprofen, enrofloxacin, buprenorphine.
• In vivo dendritic spine imaging: Two-photon microscopy (940 nm; 16× 0.8 NA objective); Z-stacks at 1 µm step, 12× zoom under ketamine/xylazine anesthesia. Spine formation/elimination quantified session-to-session; 150–200 spines per animal per session analyzed in ImageJ. Spine morphology categorized per established criteria; filopodia identified separately.
• In vivo wide-field calcium imaging: Head-fixed, freely running/resting on rotating disk; custom mesoscope with tandem lenses and sCMOS camera. Excitation 470 nm LED; emission 520/36 nm. 400×400 px, 10 fps, 15 min sessions. Concurrent IR video of whisker pad (30 fps). Processing with pySEAS ICA to reduce hemodynamic components; regions with strong expression masked via autocorrelation threshold. Whisking defined via optic flow on whisker ROI. Whole-field Ca activity computed as average dF/F0 in mask; Pearson cross-correlation with whisking magnitude; trial-aligned analyses around whisking onset; whisking-modulation computed as post-onset minus pre-onset activity; response delay computed from peak timing; pixelwise cross-correlations assessed.
• In vivo two-photon Ca imaging of L2/3 neurons: 940 nm excitation; 512×512 px at 30 fps (downsampled to 10 fps). Motion correction with ImageJ moco. ROIs manually delineated; dF/F0 computed with F0 as 50th percentile in 300 s sliding window. Transients detected with peakfinder (thresholds: 4× baseline SD; min inter-peak 0.5 s; width ≥0.3 s). Denoised traces zeroed below 2× baseline SD. Synchronous events detected by binarizing traces, summing population activity, generating 1000 circularly shuffled surrogates, and thresholding at 95th percentile of surrogates; neuron participation defined at event peak. Pairwise correlations (Pearson p) converted to distance d = √(1 − p); hierarchical clustering (complete linkage). Touch events defined as ≥1 s whisker contact with texture; responses computed as contact minus baseline windows. ROC-based detection probability with permutation tests (1000 shuffles) to classify neurons as responsive to novel, familiar, or both (NTS, FTS, non-selective).
• In vitro electrophysiology: Acute brain slices prepared from 6–8 week mice; cutting solution specified; standard patch-clamp methods (details beyond provided excerpt).

• A single post-stress dose of tabernanthalog (TBG) administered after a 7-day unpredictable mild stress (UMS) regimen reduces anxiety-like behavior in mice (EPM) and rescues deficits in sensory processing (whisker-dependent texture discrimination) and cognitive flexibility (odor discrimination/reversal).
• TBG promotes regrowth of dendritic spines on excitatory neurons that were lost during UMS.
• In somatosensory cortex, TBG decreases baseline neuronal activity and enhances whisking-modulation of activity as measured by wide-field calcium imaging.
• During a whisker-dependent texture discrimination task under head-fixation, novel textures evoke responses in a larger fraction of S1 neurons than familiar textures in control mice; this novelty-selective response is diminished by UMS and restored by TBG.
• Collectively, TBG reverses UMS-induced alterations in cortical circuit dynamics, restoring both basal activity regulation and stimulus-dependent neuronal responses.

The study addresses whether a non-hallucinogenic psychedelic analog can reverse stress-induced circuit and behavioral deficits. UMS disrupted dendritic structure and impaired cortical processing, elevating baseline activity and blunting novelty-specific responses in S1. A single post-stress dose of TBG restored spine density dynamics, reduced aberrant baseline activity, and reinstated whisking-modulated and novelty-selective neuronal responses. These circuit-level changes coincided with rescued anxiety-like behavior, sensory discrimination, and cognitive flexibility, indicating that TBG’s therapeutic effects are mediated by normalization of cortical network function. Findings support the potential of non-hallucinogenic psychedelic analogs to treat stress-related disorders by promoting structural plasticity and rebalancing cortical activity.

This work demonstrates that tabernanthalog (TBG), a non-hallucinogenic analog of 5-MeO-DMT, reverses behavioral and cortical circuit deficits induced by unpredictable mild stress. A single dose rescues anxiety-like behavior, sensory processing, and cognitive flexibility, while promoting dendritic spine regrowth and restoring appropriate basal and stimulus-modulated neuronal activity in somatosensory cortex. These findings highlight TBG as a promising therapeutic candidate for stress-related neuropsychiatric conditions and underscore the link between structural plasticity and functional circuit recovery. Future studies should define receptor-specific mechanisms, dose–response relationships, durability of effects, and generalization across brain regions, stress paradigms, and sexes.