Effects of hallucinogenic agents mescaline and phencyclidine on zebrafish behavior and physiology

Abstract

Mescaline and phencyclidine (PCP) are potent hallucinogenic agents affecting human and animal behavior. As their psychotropic effects remain poorly understood, further research is necessary to characterize phenotypes they evoke in various animal models. Zebrafish (Danio rerio) are rapidly emerging as a new model organism for neuroscience research. Here, we examine the effects of mescaline (5-20mg/l) and PCP (0.5-3mg/l) in several zebrafish paradigms, including the novel tank, open field and shoaling tests. Mescaline and PCP dose-dependently increased top activity in the novel tank test, also reducing immobility and disrupting the patterning of zebrafish swimming, as assessed by ethograms. PCP, but not mescaline, evoked circling behavior in the open field test. At the highest doses tested, mescaline markedly increased, while PCP did not affect, zebrafish shoaling behavior. Finally, 20mg/l mescaline did not alter, and 3mg/l PCP elevated, whole-body cortisol levels. Overall, our studies indicate high sensitivity of zebrafish models to hallucinogenic compounds with complex behavioral and physiological effects.

Figure 1. Behavioral effects of 20-min acute exposure to mescaline and phencyclidine (PCP) on zebrafish tested in the novel tank (Experiment 1)

Behavioral endpoints were obtained in the standard 6-min novel tank test for 5–20 mg/l mescaline (A; n = 20 per group) and 0.5–3 mg/l PCP (B; n = 13 per group). Representative 2D traces were generated by Noldus Ethovision XT7 software using the side view video-recording (the traces were examined for each experimental cohort, rated from 1 to n based on similarity, and the middle trace was selected as representative, to illustrate the patterns of zebrafish locomotion). Panel C shows the effects of drugs on the patterning of zebrafish novel tank test behavior, assessed by ethograms generated based on frequencies and transitions between each individual behavioral activity. The diameter of each circle corresponds to the frequency of each individual behavioral activity; the arrow width and direction reflect the frequency of transitions between these behaviors (asterisks next to the circles denote significant differences vs. the respective control fish behaviors; asterisks placed on top of arrows indicate significant differences in the respective transitions, compared to the respective controls). *P<0.05, **P<0.01, ***P<0.001 vs. control; post-hoc Tukey test for significant ANOVA data.

Figure 1. Behavioral effects of 20-min acute exposure to mescaline and phencyclidine (PCP) on zebrafish tested in the novel tank (Experiment 1)

Behavioral endpoints were obtained in the standard 6-min novel tank test for 5–20 mg/l mescaline (A; n = 20 per group) and 0.5–3 mg/l PCP (B; n = 13 per group). Representative 2D traces were generated by Noldus Ethovision XT7 software using the side view video-recording (the traces were examined for each experimental cohort, rated from 1 to n based on similarity, and the middle trace was selected as representative, to illustrate the patterns of zebrafish locomotion). Panel C shows the effects of drugs on the patterning of zebrafish novel tank test behavior, assessed by ethograms generated based on frequencies and transitions between each individual behavioral activity. The diameter of each circle corresponds to the frequency of each individual behavioral activity; the arrow width and direction reflect the frequency of transitions between these behaviors (asterisks next to the circles denote significant differences vs. the respective control fish behaviors; asterisks placed on top of arrows indicate significant differences in the respective transitions, compared to the respective controls). *P<0.05, **P<0.01, ***P<0.001 vs. control; post-hoc Tukey test for significant ANOVA data.

Figure 2. Behavioral effects of 20-min acute exposure to mescaline and phencyclidine (PCP) on zebrafish rotational behavior in the open field test (Experiment 2)

Rotation data represent the number of total (left + right) rotations and the percentage of animals per group displaying `high rotation' behaviors (5 or more `full' rotations) during the 6-min test (n = 13–14 per group). ANOVA results show a significant drug effect on the number of total rotation (F_(2,38) = 8.6, p<0.001) and the percentage of animals showing `high rotation' phenotype (F_(2,38) = 13.2, p<0.001). Representative traces showing rotation behavior in PCP-treated fish (vs. control) were generated by Noldus Ethovision XT7 software using the top view video-recording (only a 1-min segment of a 6-min test if presented, for clarity). In all experiments, the traces were examined for each experimental cohort, rated from 1 to n (based on similarity to each other), and the middle trace was selected as representative, to illustrate the patterns of zebrafish locomotion (see Table 1 for details of other behaviors observed in the open field test). ***P<0.001 vs. control, &P<0.05 vs. mescaline group; post-hoc Tukey test for significant ANOVA data.

Figure 3. Behavioral effects of 20-min acute exposure to mescaline (A) and phencyclidine (PCP; B) on zebrafish tested in the shoaling tests (Experiment 3)

Panel C shows typical patterns of zebrafish shoaling evoked by these drugs (representative photographs for each cohort were rated from 1 to n, based on similarity to each other, and the middle image was selected as representative, to illustrate the patterns of zebrafish shoaling). **P<0.01, ***P<0.001 vs. control (n = 24 per group); post-hoc Tukey test for significant ANOVA data.