Intraocular injection of muscimol induces illusory motion reversal in goldfish

Abstract

Induced activation of the gamma-aminobutyric acid(A) (GABA(A)) receptor in the retina of goldfish caused the fish to rotate in the opposite direction to that of the spinning pattern during an optomotor response (OMR) measurement. Muscimol, a GABA(A) receptor agonist, modified OMR in a concentration-dependent manner. The GABA(B) receptor agonist baclofen and GABA(C) receptor agonist CACA did not affect OMR. The observed modifications in OMR included decreased anterograde rotation (0.01~0.03 microM), coexistence of retrograde rotation and decreased anterograde rotation (0.1~30 microM) and only retrograde rotation (100 microM~1 mM). In contrast, the GABA(A) receptor antagonist bicuculline blocked muscimolinduced retrograde rotation. Based on these results, we inferred that the coding inducing retrograde movement of the goldfish retina is essentially associated with the GABA(A) receptor-related visual pathway. Furthermore, from our novel approach using observations of goldfish behavior the induced discrete snapshot duration was approximately 573 ms when the fish were under the influence of muscimol.

Keywords: Discrete snapshot duration; Goldfish; Illusory motion reversal (IMR); Optomotor response (OMR); Retina.

Fig. 1

OMR of a goldfish before (■) and after (▧) administration of three concentrations of muscimol (A), baclofen (B), and CACA (C). All drugs were independently administered five times. Muscimol-induced negative OMR represents the reverse rotation of a goldfish to the direction of pattern rotation. Here and in subsequent figures, unless otherwise indicated the error bar represents±standard error of the mean, ^*indicates p<0.05 and n represents the number of goldfish.

Fig. 2

The relationship between muscimol concentration and normalized OMR. Eleven concentrations of muscimol from 0.01 µM to 1 mM were used (n=5 for each concentration). At certain concentrations, the same goldfish showed both negative and positive OMR. To account for this, each fish treated with concentrations ranging from 0.1~30 µM was measured twice as much. Therefore, the total number of fish used in the experiment was 55, but 30 of were tested and measured twice as much as the remaining 25. As the muscimol concentration increased, there were 3 distinctive OMR results: reduction in anterograde rotation, coexistence of retrograde rotation and reduced anterograde rotation, and retrograde rotation only. The diagram, which shows the anterograde and retrograde rotation, is shown on the graph for reference and clarity.

Fig. 3

OMR as to GABA receptor related drugs. (A) Co-injection (n=5) of 1 mM muscimol (MUS) and 2 mM bicuculline (BIC) inhibited the negative OMR that muscimol had induced. (B) OMR using the two concentrations of bicuculline. Bicuculline alone markedly reduced anterograde OMR (n=5).

Fig. 4

Goldfish rotation versus pattern rotation. (A) Number of rotations depending on various pattern velocities after the administration of 1 mM muscimol (n=5 for each velocity). The reversed rotation due to muscimol was the greatest at a pattern velocity of 12 rpm. (B) Rotation of goldfish to low speeds in the control condition (n=5 in different pattern rotation speeds). From this relationship, a linear equation of y=0.565x-0.231 was obtained. Using this, we could predict the pattern's velocity to be 3.12 rpm when a goldfish rotated at a velocity of 1.532 rpm.