Psilocybin: Biphasic dose-response effects on the acoustic startle reflex in the rat
Michael T. Davis, James K. Walters
Pharmacology Biochemistry and Behavior April 1, 1977 DOI: 10.1016/0091-3057(77)90180-0 via OpenAlex
Summary
AI-generated from the abstractPsilocybin has a biphasic dose-response effect on the startle reflex in rats. Low doses (0.75-2.0 mg/kg) increased startle amplitude, while high doses (4.0-8.0 mg/kg) depressed it. Equimolar doses of psilocin produced comparable effects. This pattern is consistent with the hypothesis that startle increases when midbrain raphe neuron firing is selectively inhibited but decreases when neurons postsynaptic to raphe cells are also inhibited.
Study at a glance
| Characteristics | Experimental study Peer reviewed |
|---|---|
| Sample size | 70 |
| Population | Rats |
| Interventions | psilocybin psilocin |
| Dose | 0.25, 0.50, 0.75, 1.0, 2.0, 4.0, 8.0 mg/kg psilocybin; 0.71 or 5.70 mg/kg psilocin |
| Topics | Psilocybin |
| Keywords | Startle response Moro reflex Hallucinogen Acoustic startle reflex |
| Citations | 26 |
| Key finding | Psilocybin produces a biphasic dose-response effect on the startle reflex, with low doses increasing and high doses decreasing startle amplitude. |
Abstract
The startle reflex was measured in 7 groups of 10 rats each after intraperitoneal injection of saline or 0.25, 0.50, 0.75, 1.0, 2.0, 4.0 or 8.0 mg/kg psilocybin. Low doses (0.75-2.0 mg/kg) increased startle amplitude whereas high doses (4.0-8.0 mg/kg) depressed startle. Selected low (0.71 mg/kg) or high (5.70 mg/kg) doses of psilocin also had a biphasic dose-response effect on startle comparable in magnitude to equimolar doses of psilocybin. This biphasic dose-response relationship of the indole hallucinogen, psilocybin, on startle is consistent with the hypothesis that startle is increased when the firing rates of midbrain raphe neurons are selectively inhibited but is depressed when neurons postsynaptic to raphe cells are also inhibited.