The effect of medial prefrontal cortex inactivation on psychedelic-mediated emergence from anesthesia

Abstract

Serotonergic psychedelics are being explored as therapeutic agents for mental health disorders and have also been shown to promote wakefulness. In a recently completed study (reported as preliminary findings), we showed that intravenous administration of 2,5-Dimethoxy-4-iodoamphetamine (DOI), a classic serotonergic psychedelic, can induce wakefulness and reverse the state of anesthesia produced by molecularly distinct anesthetics, propofol (n=21 rats) or isoflurane (n=14 rats), but the brain site(s) responsible for this effect remains unknown. It is known that serotonergic psychedelics (including DOI) act via 5-HT2A receptors. The 5-HT2A receptors are densely expressed in the medial prefrontal cortex (mPFC), which has been shown in our previously published studies as a key node in the arousal promoting circuitry. Therefore, in the current study, we hypothesized that inactivation of the mPFC via local tetrodotoxin microinjection will attenuate the arousal promoting effects of DOI. To test this hypothesis, adult Sprague Dawley rats (n=5 male, 1 female) were surgically equipped with electrodes to record electroencephalogram, a chronic catheter in jugular vein for propofol/DOI delivery, and bilateral guide tubes aimed at mPFC for microinjection of 156 μM tetrodotoxin (TTX) or 0.9% saline (SAL, vehicle control). The rats were provided 10-14 days of post-surgical recovery after which the rats received a bilateral microinjection (500 nL) of TTX or SAL into the mPFC. Forty-five minutes after the TTX or SAL injection, the rats were anesthetized with intravenous propofol infusion (600-1000 µg/kg/min). The rats were maintained on propofol anesthesia for 40 minutes after which DOI was administered intravenously (0.5 mg/kg over a 1-minute period) and the behavioral changes in the first 5-minutes after the end of DOI infusion were noted. The anesthetic delivery was stopped after 20 minutes and the time to return of righting reflex (RORR) (a surrogate for the return of consciousness) was measured. All experimental sessions were videotaped, and an investigator blinded to the experimental conditions scored the behavioral changes. Contrary to our hypothesis, the results show that intravenous DOI infusion in anesthetized rats produced behavioral arousal (i.e., head movements, forepaw treading, attempts at or return of righting) irrespective of whether the mPFC was intact (i.e., SAL condition) or was inactivated via local TTX injection. Furthermore, as compared to the emergence time in the rats with inactivated mPFC that did not receive intravenous DOI (mean ± sd: 563.17 ± 323.73 seconds), the rats that received intravenous DOI showed a decrease in the time to RORR, irrespective of whether the mPFC was intact (i.e., SAL group; mean ± sd: 284.67 ± 88.87 seconds) or was inactivated via local TTX injection (mean ± sd: 355.5 ± 232.93 seconds). These preliminary findings indicate that DOI accelerates emergence from propofol anesthesia by targeting cortical areas other than mPFC or subcortical structures. Additional experiments are in progress to determine the effect of inactivation of parietal cortex or subcortical structures on DOI-induced reversal of general anesthesia. Department of Anesthesiology, University of Michigan, Ann Arbor, MI Post-Baccalaureate Research Education Program (U-M PREP), University of Michigan, Ann Arbor, MI This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.