Effect of Psilocybin and Ketamine on Brain Neurotransmitters, Glutamate Receptors, DNA and Rat Behavior

Abstract

Clinical studies provide evidence that ketamine and psilocybin could be used as fast-acting antidepressants, though their mechanisms and toxicity are still not fully understood. To address this issue, we have examined the effect of a single administration of ketamine and psilocybin on the extracellular levels of neurotransmitters in the rat frontal cortex and reticular nucleus of the thalamus using microdialysis. The genotoxic effect and density of glutamate receptor proteins was measured with comet assay and Western blot, respectively. An open field test, light-dark box test and forced swim test were conducted to examine rat behavior 24 h after drug administration. Ketamine (10 mg/kg) and psilocybin (2 and 10 mg/kg) increased dopamine, serotonin, glutamate and GABA extracellular levels in the frontal cortex, while psilocybin also increased GABA in the reticular nucleus of the thalamus. Oxidative DNA damage due to psilocybin was observed in the frontal cortex and from both drugs in the hippocampus. NR2A subunit levels were increased after psilocybin (10 mg/kg). Behavioral tests showed no antidepressant or anxiolytic effects, and only ketamine suppressed rat locomotor activity. The observed changes in neurotransmission might lead to genotoxicity and increased NR2A levels, while not markedly affecting animal behavior.

Keywords: DNA damage; GABA; dopamine; forced swim test; glutamate; glutamate receptors; light–dark box test; microdialysis; open field test; serotonin.

Figure 1

The time-course (A,C,E,G) and total (B,D,F,H) effect of psilocybin (2 and 10 mg/kg) and ketamine (10 mg/kg) on the dopamine (DA), serotonin (5-HT), glutamate (GLU) and γ-aminobutyric acid (GABA) extracellular levels in the rat frontal cortex. The total effect is calculated as an area under the concentration-time curve (AUC) and expressed as a percentage of the basal level. Values are the mean ± SEM (n is given under the name of the group). The drug injection is indicated with an arrow. Filled symbols or * show statistical differences (p < 0.001) between control and drug treatment groups; ^ p < 0.001 show differences between psilocybin 2 and 10 mg/kg groups as estimated by repeated measures ANOVA (time-course) or one-way ANOVA (total effect) followed by Tukey’s post hoc test.

Figure 2

The time-course (A,C) and total (B,D) effect of psilocybin (2 and 10 mg/kg) and ketamine (10 mg/kg) on the glutamate (GLU) and γ-aminobutyric acid (GABA) extracellular levels in the rat reticular nucleus of the thalamus. The total effect is calculated as an area under the concentration-time curve (AUC) and expressed as a percentage of the basal level. Values are the mean ± SEM (n is given under the name of the group). The drug injection is indicated with an arrow. Filled symbols or * show statistical differences (p < 0.03–0.001) between control and drug treatment groups; ^ p < 0.005–0.001 show differences between psilocybin 2 and 10 mg/kg groups as estimated by repeated measures ANOVA (time-course) or one-way ANOVA (total effect) followed by Tukey’s post hoc test.

Figure 3

Levels of NMDA receptor subunits (GluN2A and GluN2B; (A) and AMPA receptor subunits (GluA1 and GluA2; (D) in the rat frontal cortex estimated 24 h after psilocybin (2 and 10 mg/kg) or ketamine (10 mg/kg) administration. The data are shown as percentages of the levels of the appropriate control groups. Each data point represents the mean ± SEM (n is given under the name of the group). Only in group GluN2A are data given in duplicates. * p < 0.05 vs. appropriate control group (one-way ANOVA followed by Tukey’s post hoc test). Examples of photomicrographs of the immunoblots using GluN2A and GAPDH antibodies (B), GluN2B and GAPDH antibodies (C), GluA1 and GAPDH antibodies (E) and GluA2 and GAPDH antibodies (F).

Figure 4

The effect of psilocybin (2 and 10 mg/kg), ketamine (10 mg/kg) and MDMA (10 mg/kg) on the oxidative damage of DNA in nuclei of the rat frontal cortex (A) and hippocampus (B) in the comet assay estimated 7 days after treatment. Data are the mean ± SEM (n is given under the name of the group) and represent tail moment shown as the product of the tail length and the fraction of total DNA in the tail. * p < 0.001–0.05 compared to the control (one-way ANOVA followed by Tukey’s post hoc test).

Figure 5

The effect of psilocybin (2 and 10 mg/kg) and ketamine (10 mg/kg) on locomotor behavior in the open field test (OF) and on activity of rats in the light–dark box (LDB) test 24 h after administration. The time spent on walking (A), the number of crossing episodes (B) in the OF test and ambulatory distance (C) and time spent (D) in the light and dark zone in the LDB test. Values are the mean ± SEM (n is given under or next to the name of the group). * p < 0.001–0.05 compared to the control; ^ p < 0.05 psilocybin 2 mg/kg compared to psilocybin 10 mg/kg; # p < 0.001 light vs. dark (one-way ANOVA or two-way ANOVA followed by Tukey’s post hoc test).

Figure 6

The effect of psilocybin (2 and 10 mg/kg) and ketamine (10 mg/kg) on the immobility (A), climbing (B) or swimming (C) time of rats in the forced swim test (FST) estimated 24 h after administration. Data are the mean ± SEM (n is given under the name of the group). * p < 0.001–0.01 compared to the control; ^ p < 0.05 psilocybin 2 mg/kg compared to psilocybin 10 mg/kg (one-way ANOVA followed by Tukey’s post hoc test).