The Behavioral and Pharmacological Actions of NMDA Receptor Antagonism are Conserved in Zebrafish Larvae

Abstract

Dizocilpine maleate (MK-801) is one of several NMDA receptor antagonists that is widely used to pharmacologically model the symptoms of psychosis and schizophrenia in animals. MK-801 elicits behaviors in adult zebrafish (Danio rerio) that are phenotypically consistent with behaviors observed in humans and rodents exposed to tbhe drug. However, the molecular and cellular processes that mediate the psychotomimetic, cognitive and locomotive behaviors of MK-801 are unclear. We exposed zebrafish larvae to MK-801 to assess their merit as a model organism to elucidate the behavioral effects of NMDA receptor blockade. Zebrafish larvae were acutely immersed in MK-801 to assess the effect on spontaneous swimming. MK-801 caused a time- and dose-dependent increase in larval swim speed, and the peak response (a five-fold increase in swim speed) was evoked by a three h exposure to a 20 uM dose. Zebrafish larvae did not exhibit sensitivity to the locomotor effects of MK-801 until 5 dpf, suggesting a critical role for developmental in sensitivity to the drug. Exposure to the low potency NMDA antagonist, memantine, did not alter the swim speed of zebrafish larvae. Co-immersion in D(1) or D(2) dopamine receptor antagonists did not disrupt the time course or magnitude of the increase in swim speed, suggesting dopaminergic signaling is not required for the locomotor actions of MK-801. Our findings of the behavioral actions of MK-801 in zebrafish larvae are consistent with previous observations in mammals and imply that the physiological, cellular and molecular processes disrupted by MK-801 are conserved in zebrafish larvae. These data suggest that the zebrafish larvae is a valid and useful model to elucidate neurobehavioral aspects of NMDA receptor antagonism and may provide insight to the neurobiology of psychosis and schizophrenia.

Figure 1

Temporal effects of MK-801 on locomotor activity of zebrafish larvae. Results are presented as means + S.E.M. N = 4 groups of larvae per condition, F(5, 12) = 5.60, p = 0.0068, *vs 0h, p < 0.05 by Tukey's HSD).

Figure 2

Dose-dependency of the locomotor effect of MK-801. Changes in spontaneous locomotion (Δ spontaneous locomotion) were calculated by (AVG Speed at t_4h − AVG Speed at t_0h) at each dose. Values are presented as means ± S.E.M. Dashed line represents a non-linear regression of the data (Sigma Plot 10); calculated EC₅₀ = 10.3μM; R² = 0.9917. N = 4-8 groups of larvae per concentration, F(5, 18) = 8.00. p = 0.0004, *dose vs vehicle (0 μM), p < 0.05 by Tukey's HSD).

Figure 3

Effect of memantine on spontaneous locomotion of zebrafish larvae. Changes in spontaneous locomotion (Δ spontaneous locomotion) were calculated by (AVG Speed at t_4h – AVG Speed at t_0h) at each dose. Values are presented as means ± S.E.M. N = 4 groups of larvae per concentration [F(5, 18) = 0.30, p = 0.91].

Figure 4

Effect of development on sensitivity to locomotor effects of MK-801. Changes in spontaneous locomotion (Δ spontaneous locomotion) were calculated by (AVG Speed at t_4h – AVG Speed at t_0h) at the developmental times indicated. Values are presented as means + S.E.M. N = 4-8 groups of larvae per concentration, F(5, 18) = 6.88. p = 0.0002, *Control vs 50 μm MK, p < 0.05 by Tukey's HSD).

Figure 5

Effect of dopamine receptor antagonists on the locomotor effects of MK-801. Groups of zebrafish larvae (5dpf) were concurrently exposed to 50 μM MK-801 + 50 μM Sulpiride; 50 μM MK-801 + 50 μM SKF-83566; or 50 μM MK-801 + 50 μM Sulpiride + 50 μM SKF-83566. Dashed line represents the time course of the locomotor response to 50 μM MK-801 shown in Fig. 1 for compairson. Values are presented as means + S.E.M. N = 4 groups of aniamls per drug combination [F(5, 18) = 14.27. p = 0.0001].