A pill form of ketamine cut dissociation to near-zero vs. nasal spray's 29.6-point spike — but missed its main antidepressant target

Key Findings

🐀 In rats, blocking a specific serotonin receptor (5-HT2B) wiped out psilocybin's antidepressant-like effects — without touching its psychedelic signature

• A single dose of psilocybin (0.32 mg/kg) in Wistar rats reduced immobility in the forced swim test both rapidly (day 1) and durably (day 21) — a behavioral pattern used as a proxy for antidepressant activity.

• Pretreatment with a 5-HT2B receptor blocker (RS-127445) dose-dependently reversed both the rapid and sustained antidepressant-like effects — but left the head-twitch response (a rodent proxy for psychedelic effects, driven by 5-HT2A receptors) completely intact.

• This suggests psilocybin's antidepressant-like effects in this model may be separable from its psychedelic effects at the receptor level — the 'trip' and the 'treatment' may run through different biological pathways.

Important caveat: This is rat data using a behavioral model, not human clinical outcomes. Whether 5-HT2B receptors play the same role in human depression is unknown.

🔬 Ketamine physically docks onto opioid receptors — new structural images show how

• Researchers captured high-resolution structural images of human opioid receptors bound to both ketamine and its parent compound phencyclidine (PCP), providing direct molecular-level evidence that both drugs can bind and activate these receptors — not just the NMDA receptors they're classically associated with.

• Compared to PCP, ketamine showed more dynamic binding behavior in the receptor's active site, which may contribute to differences in how the two drugs behave pharmacologically.

• The team also captured the first structural image of the kappa opioid receptor in its ligand-free (unoccupied) state, offering a baseline view of the receptor before any drug binds.

🧠 Psilocybin's effect on 'brain entropy' is real — but it's not one single thing

• Across 121 pre- and post-psilocybin brain scans from 28 healthy participants, only some of the 14 entropy metrics tested showed consistent increases after psilocybin: Shannon entropy, path-length, instantaneous correlations, brain-state switching, and short-timescale sample entropy all showed significant positive associations.

• 8 of the 14 metrics showed no significant effect at all, and Lempel-Ziv complexity (one of the most commonly cited measures) showed inconsistent results across analysis pipelines.

• Critically, the entropy metrics that did show effects were poorly correlated with each other — meaning they're not measuring the same underlying brain process, even though they share a name.

🌿 Why do plants and fungi make hallucinogens? A chemical ecology review offers some context

• A review in PNAS synthesizes evidence from chemical ecology, genomics, and evolutionary biology to examine why hallucinogenic compounds — phenethylamines, indolealkylamines, terpenoids — appear independently across plants, fungi, and animals.

• The leading ecological hypothesis is that these molecules may function as behavioral manipulators of herbivores or pollinators, rather than evolving for any human-relevant purpose — and human psychoactivity may be a byproduct of molecules shaped by interactions with animals that share deeply conserved receptor systems.

• On endogenous (naturally occurring in the body) tryptamines like DMT, the review argues the leading hypothesis points toward sigma-1 receptor-mediated stress responses and cell protection — not an inherent hallucinogenic function in mammals.

🎵 Music during psychedelic therapy amplifies emotions and increases brain 'disorder' — but the evidence base is thin

• A scoping review of 19 studies (total of just 330 human participants) found that music during psychedelic sessions appears to work through three pathways: amplifying and intensifying emotions, activating brain networks linked to meaning-making and visual imagery, and increasing overall neural entropy (a measure of signal complexity).

• Psilocybin and LSD were the most studied compounds; no studies on MDMA and music met inclusion criteria.

• The review flagged major methodological gaps: music conditions varied widely across studies, sample sizes were small, and no studies have directly compared different music types in a controlled way.

💉 Ketamine's abuse risk appears low in supervised clinical settings — but the picture is murkier outside them

• A systematic review of 30 studies (25 clinical, 5 preclinical) found that clinical and randomized trials consistently reported minimal craving, dose escalation, or misuse when ketamine or esketamine was given in structured, monitored settings.

• In preclinical (animal) models, (S)-ketamine produced reward-related behaviors and locomotor sensitization; racemic ketamine showed reinforcing effects at higher doses; while (R)-ketamine showed minimal reinforcing effects — suggesting the three forms may carry meaningfully different abuse profiles.

• Abuse and misuse cases were identified largely in case reports where appropriate monitoring was absent, not in supervised clinical trials.