Guzzo, P. | bioRxiv Science

bioRxiv2024

Psilocybin induces dose-dependent changes in functional network organization in rat cortex

Psilocybin produces an altered state of consciousness in humans and is associated with complex spatiotemporal changes in brain networks. Given the emphasis on rodent models for mechanistic studies, there is a need for characterization of the effect of psilocybin on brain-wide network dynamics. Previous rodent studies of psychedelics, using electroencephalogram, have primarily been done with sparse electrode arrays that offered limited spatial resolution precluding network level analysis, and have been restricted to lower gamma frequencies. Therefore, in the study, we used electroencephalographic recordings from 27 sites (electrodes) across rat cortex (n=6 male, 6 female) to characterize the effect of psilocybin (0.1 mg/kg, 1 mg/kg, and 10 mg/kg delivered over an hour) on network organization as inferred through changes in node degree (index of network density) and connection strength (weighted phase-lag index). The removal of aperiodic component from the electroencephalogram localized the primary oscillatory changes to theta (4-10 Hz), medium gamma (70-110 Hz), and high gamma (110-150 Hz) bands, which were used for the network analysis. Additionally, we determined the concurrent changes in theta-gamma phase-amplitude coupling. We report that psilocybin, in a dose-dependent manner, 1) disrupted theta-gamma coupling [p<0.05], 2) increased frontal high gamma connectivity [p<0.05] and posterior theta connectivity [p[≤]0.049], and 3) increased frontal high gamma [p<0.05] and posterior theta [p[≤]0.046] network density. The medium gamma frontoparietal connectivity showed a nonlinear relationship with psilocybin dose. Our results suggest that high-frequency network organization, decoupled from local theta-phase, may be an important signature of psilocybin-induced non-ordinary state of consciousness.

neuroscience↗

bioRxiv2023

Intravenous psilocybin administration attenuates mechanical hypersensitivity in a rat model of chronic pain

There is a renewed interest in the therapeutic potential of psychedelics, including psilocybin, in treating mental health disorders. However, there are no data on the efficacy of psilocybin in alleviating chronic pain. In this study, we investigated the effect of psilocybin on mechanical hypersensitivity and thermal hyperalgesia in a rat model of formalin-induced chronic pain. Adult male and female rats were surgically implanted with a jugular vein catheter for psilocybin or saline administration. After two weeks of post-surgical recovery and conditioning, baseline responses to mechanical (von Frey assay) and thermal (hot plate assay) stimuli were measured. Twenty-four hours after baseline measurements, rats received a subcutaneous injection of formalin (5%, 50{micro}L) into one of the hind paws and 2h later, responses to the mechanical and thermal stimuli were measured. Twenty-four hours after formalin injection, rats received an intravenous bolus of 1 mg/kg psilocybin (n=14) or 10 mg/kg psilocybin (n=12) or saline (n=13), and approximately 3h later, responses to the mechanical and thermal stimuli were measured. Rats were tested every other day during week 1, and then weekly for the next 3 weeks. Formalin injection induced thermal hyperalgesia and bilateral mechanical hypersensitivity in the hind paws of all rats. Intravenous psilocybin produced significant attenuation (p<0.05) of the formalin-induced bilateral mechanical hypersensitivity for 28 days but had limited effect (p<0.05 only on days 1, 3, 5, and 21) on thermal hyperalgesia. These data demonstrate that a single intravenous bolus of psilocybin can attenuate indices of chronic pain in a rat model.

neuroscience↗