Unraveling psilocybin's therapeutic potential: behavioral and neuroplasticity insights in Wistar-Kyoto and Wistar male rat models of treatment-resistant depression

Abstract

Rationale: Our study aimed to unravel the unknown mechanisms behind the exceptional efficacy of Psilocybin (PSI) in treating treatment-resistant depression (TRD). Focusing on Wistar-Kyoto (WKY) rats with a TRD phenotype and Wistar (WIS) rats as a normative comparison, we investigated behavioral and neuroplasticity-related responses to PSI, striving to shed light on the distinctive features of its antidepressant effects.

Objectives: We set out to assess the behavioral impact of acute and prolonged PSI administration on WKY and WIS rats, employing Novel Object Recognition (NORT), Social Interaction (SI), and Forced Swimming Test (FST). Our secondary objectives involved exploring strain-specific alterations in neuroplasticity-related parameters, including brain-derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton-associated protein (Arc).

Methods: Conducting post-acute and extended assessments after a single PSI administration, we applied behavioral tests and biochemical analyses to measure serum BDNF levels and neuroplasticity-related parameters in the prefrontal cortex. Statistical analyses were deployed to discern significant differences between the rat strains and assess the impact of PSI on behavioral and biochemical outcomes.

Results: Our findings uncovered significant behavioral disparities between WKY and WIS rats, indicating passive behavior and social withdrawal in the former. PSI demonstrated pronounced pro-social and antidepressant effects in both strains, each with its distinctive temporal trajectory. Notably, we identified strain-specific variations in BDNF-related signaling and observed the modulation of Arc expression in WKY rats.

Conclusions: Our study delineated mood-related behavioral nuances between WKY and WIS rat strains, underscoring the antidepressant and pro-social properties of PSI in both groups. The distinct temporal patterns of observed changes and the identified strain-specific neuroplasticity alterations provide valuable insights into the TRD phenotype and the mechanisms underpinning the efficacy of PSI.

Keywords: Activity-regulated cytoskeleton-associated protein (Arc); Brain-derived neurotrophic factor (BDNF); Long-term effect; Neuroplasticity; Psilocybin; Social interaction; Treatment-resistant depression; Weight gain; Wistar Kyoto rats.

Fig. 1

(A) Experimental paradigm presenting the timeline of behavioral procedures and biochemical analyses. The behavioral procedures spanned over 23 days, and on the 24th day, animals were sacrificed, and tissue was collected for biochemical analyses. (B) Effect of psilocybin on weight gain. Body weight was measured on the day of PSI administration and 23 days after PSI administration. WKY rats are depicted as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. In WIS rats, there was a significant decrease in body weight gain [%] compared to the vehicle-treated group (**p < 0.01, two-way ANOVA followed by Tukey’s multiple comparison test)

Fig. 2

(A) Discrimination Index (DI) in the novel object recognition task (NORT). The acquisition trial (T1) in NORT 1 was performed 4 h after PSI administration (A), and in NORT 2 it was performed 6 days after PSI administration. The retention trials (T2) was conducted 24 h following T1. DI was defined as the difference in exploration time between the novel object and the familiar one in T2, divided by the total exploration time. The DI was calculated for all groups, and data are presented as the mean ± S.E.M., n = 9–10 rats per group. WKY rats are depicted as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. According to ANOVA and subsequent post hoc pairwise comparisons, a significant inter-strain difference in DI between WIS and WKY rats was observed, *p < 0.05; **p < 0.01. (B) Outcome measures of the Social Interaction (SI) tests. The SI test was performed 2 days (A) and 8 days (B) after PSI administration. During both SI tests, rats were assessed with a novel social partner for 5 min in the open field. SI total time summarizes all data from sniffing, anogenital sniffing, grooming, following, climbing, and crawling behaviors. Data are presented as mean ± SEM, n = 9–10 per group. WKY rats are depicted as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. According to repeated measures ANOVA and post hoc pairwise comparisons, in SI 1 test, there was a statistically significant increase in SI time after PSI treatment in WIS rats. In SI 2 test, the increase in social interaction time reached the level of significance in WKY rats, **p < 0.01. Times spent for specific types of behavior are presented in detail in Figure S2 in the supplementary material. (C) Outcomes of the Forced Swim Test (FST) performed 9 days after PSI administration (A, C) and 23 days after PSI administration (B, D). WKY rats are depicted as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. According to repeated measures ANOVA and post hoc pairwise comparisons, there was a significant inter-strain difference in immobility time in FST 1 between WIS and WKY rats (****p < 0.0001). Additionally, in FST 1 in WKY rats, there was a decrease in immobility after PSI administration. This decrease in immobility occurred concomitantly with an increase in climbing (C) (*p < 0.05 vs. the vehicle group). In FST 2, there was a significant decrease in immobility time after PSI administration in WIS rats (B). This decrease in immobility occurred together with increases in swimming and climbing (D) (*p < 0.05, **p < 0.01 vs. the vehicle group). Data are presented as the mean ± SEM (n = 7–10 per group)

Fig. 3

Fold changes in the mRNA expression of neurotrophins and their receptors. Gene expression was measured in the prefrontal cortex. Individuals are represented in all the graphs with n = 7–10 per group. WKY rats are depicted as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. Groups treated with psilocybin (PSI) are shown in red. Statistical analyses were performed with two-way ANOVA with Tukey multiple comparisons post hoc test. Statistically significant changes between groups are indicated as *p < 0.05, **p < 0.01, and ****p < 0.0001; Abbreviations: Ntrk1—neurotrophic receptor tyrosine kinase 1; Ntrk2—neurotrophic receptor tyrosine kinase 2; Ntrk3—neurotrophic receptor tyrosine kinase 3; Ngfr—nerve growth factor receptor; Bdnf—brain-derived neurotrophic factor; Ngf—nerve growth factor; Ntf3—neurotrophin 3; Ntf4—neurotrophin 4

Fig. 4

(A) Fold changes in the mRNA expression of selected genes involved in synaptic plasticity. Gene expression was measured in the prefrontal cortex. Individuals are shown in all the graphs with n = 7–10 per group. WKY rats are presented as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. Groups treated with psilocybin (PSI) are shown in red. Statistical analyses were performed with two-way ANOVA with Tukey multiple comparisons post hoc test. Statistically significant changes between groups are indicated as *p < 0.05 and **p < 0.01; Abbreviations: Arc—activity-regulated cytoskeletal-associated protein; Gria1—glutamate receptor, ionotropic, AMPA1 (alpha 1); Gria2—glutamate receptor, ionotropic, AMPA2 (alpha 2); Psd95—postsynaptic density protein 95; St8sia2—ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 2; St8sia4—ST8 alpha-N-acetyl-neuraminide alpha-2,8-sialyltransferase 4. B) The normalized expression of ARC protein in the prefrontal cortex was measured by Western blot analysis. Individuals are shown in all the graphs with n = 7–10 per group. WKY rats are presented as rhomboid symbols and grey shaded bars, while WIS rats are represented as squared symbols and white bars. Groups treated with psilocybin (PSI) are shown in red. Statistical analyses were performed with two-way ANOVA with Tukey multiple comparisons post hoc test. Statistically significant changes between groups are indicated as **p < 0.01 and #p < 0.05. Representative Western blot image for ARC in PCX