Neuropharmacology of vision in goldfish: A review

The impact of ocean acidification on the eye, cuttlebone and behaviors of juvenile cuttlefish (Sepiella inermis)

The cuttlefish (Sepiella inermis) is an economically important species in the coastal seas of China. The impacts of ocean acidification on the ability of juvenile cuttlefish to select a suitable habitat, its hunting and swimming behavior, remains unknown. We examined behavior-related responses and the eye and cuttlebone structure of juvenile cuttlefish following short-term exposure to CO₂-enriched seawater. The predation success rate decreased with the elevation in CO₂ concentration. In the CO₂ treatment groups, cuttlefish spent more time in the dark zone and the average swimming speed and total swimming distance significantly decreased. The structure of the retina and cuttlebone was affected by seawater acidification. Moreover, apoptotic cells were significantly increased in the eyes. In the wild, the impairment of the eye and cuttlebone may decrease the predation ability of juvenile cuttlefish and negatively affect their ability to select a suitable habitat, which would be detrimental to its population.

Visual perception of planar-rotated 2D objects in goldfish (Carassius auratus)

This study examined the ability of goldfish to visually identify 2D objects rotated in the picture plane. This ability would be adaptive for fish since they move in three dimensions and frequently view objects from different orientations. Goldfish performed a two-alternative forced choice task in which they were trained to discriminate between two objects at 0°, then tested with novel aspect angles (+/- 45°, +/- 90°, +/- 135°, 180°). Stimuli consisted of an arrow and half circle (Experiment 1) and line drawings of a turtle and frog (Experiments 2 and 3). In the first two experiments, the S+ and S- were presented at the same aspect angle. Performance in these experiments exceeded chance on four of seven novel aspect angles. Overall accuracy was not significantly different with complex stimuli (animal drawings) vs. simple stimuli (geometric shapes). In Experiment 3, when fish were tested with the S+ at varying aspect angles and the S- always presented at 0°, the fish failed to discriminate among the stimuli at all but one aspect angle. These goldfish viewing planar-rotated 2D objects did not display viewpoint-invariant performance, nor did they show a systematic decrement in performance as a function of aspect angle.

Goldfish morphology as a model for evolutionary developmental biology

Morphological variation of the goldfish is known to have been established by artificial selection for ornamental purposes during the domestication process. Chinese texts that date to the Song dynasty contain descriptions of goldfish breeding for ornamental purposes, indicating that the practice originated over one thousand years ago. Such a well-documented goldfish breeding process, combined with the phylogenetic and embryological proximities of this species with zebrafish, would appear to make the morphologically diverse goldfish strains suitable models for evolutionary developmental (evodevo) studies. However, few modern evodevo studies of goldfish have been conducted. In this review, we provide an overview of the historical background of goldfish breeding, and the differences between this teleost and zebrafish from an evolutionary perspective. We also summarize recent progress in the field of molecular developmental genetics, with a particular focus on the twin-tail goldfish morphology. Furthermore, we discuss unanswered questions relating to the evolution of the genome, developmental robustness, and morphologies in the goldfish lineage, with the goal of blazing a path toward an evodevo study paradigm using this teleost species as a new model species. For further resources related to this article, please visit the WIREs website.

Color- and motion-specific units in the tectum opticum of goldfish

Extracellular recordings were performed from 69 units at different depths between 50 and [Formula: see text]m below the surface of tectum opticum in goldfish. Using large field stimuli (86[Formula: see text] visual angle) of 21 colored HKS-papers we were able to record from 54 color-sensitive units. The colored papers were presented for 5[Formula: see text]s each. They were arranged in the sequence of the color circle in humans separated by gray of medium brightness. We found 22 units with best responses between orange, red and pink. About 12 of these red-sensitive units were of the opponent "red-ON/blue-green-OFF" type as found in retinal bipolar- and ganglion cells as well. Most of them were also activated or inhibited by black and/or white. Some units responded specifically to red either with activation or inhibition. 18 units were sensitive to blue and/or green, 10 of them to both colors and most of them to black as well. They were inhibited by red, and belonged to the opponent "blue-green-ON/red-OFF" type. Other units responded more selectively either to blue, to green or to purple. Two units were selectively sensitive to yellow. A total of 15 units were sensitive to motion, stimulated by an excentrically rotating black and white random dot pattern. Activity of these units was also large when a red-green random dot pattern of high L-cone contrast was used. Activity dropped to zero when the red-green pattern did not modulate the L-cones. Neither of these motion selective units responded to any color. The results directly show color-blindness of motion vision, and confirm the hypothesis of separate and parallel processing of "color" and "motion".

Levodopa as a possible treatment of visual loss in nonarteritic anterior ischemic optic neuropathy

PURPOSE

To determine the clinical effectiveness and potential neuroprotection of levodopa in improving visual acuity, visual field, and retinal nerve fiber layer (RNFL) thickness in eyes affected by NAION.

METHOD

Retrospective cohort study involving 59 eyes of 59 participants with NAION who were evaluated within 15 days of NAION onset. Participants received 25 mg carbidopa/100 mg levodopa three times daily with meals for 12 weeks (levodopa group) or were untreated (control group). Best-corrected visual acuity converted to logMAR, mean deviation (MD) threshold sensitivity on automated perimetry, and mean RNFL thickness on optical coherence tomography (OCT) were assessed. The primary outcome was the categorization of eyes into improved visual acuity (by 0.3 logMAR difference), worsened visual acuity (by 0.3 logMAR difference), or no change in visual acuity. The proportions in each category were compared between the levodopa and control groups.

RESULTS

Among participants with 20/60 or worse initial visual acuity, levodopa-treated participants had significant improvement (P < 0.0001) in the mean change from initial to final logMAR visual acuity of -0.74 ± 0.56 (95 % CI, -0.98 to -0.50), while the mean change for the control group at -0.37 ± 1.09 (95 % confidence interval estimate, -1.00 to +0.26) was not significant (P = 0.23). A significant difference between groups was observed (P = 0.0086) such that 19/23 (83 %) in the levodopa group improved and none got worse, as compared with 6/14 (43 %) in the control group improving while four (29 %) worsened. The change in visual field MD and RNFL thickness on OCT showed no significant difference at P = 0.23 and P = 0.75 respectively. No levodopa-treated participant had any adverse event from the levodopa.

CONCLUSIONS

Treatment within 15 days of onset of NAION with levodopa improved central visual acuity by an average of 6 lines on Snellen acuity chart. Levodopa may promote neuroprotection of the maculopapular retinal ganglion cell fibers in NAION.

The antidepressant tranylcypromine alters cellular proliferation and migration in the adult goldfish brain

The goldfish (Carassius auratus) is a widely studied vertebrate model organism for studying cell proliferation in the adult brain, and provide the experimental advantage of growing their body and brain throughout their ∼30-year life time. Cell proliferation occurs in the teleost brain in widespread proliferation zones. Increased cell proliferation in the brain has been linked to the actions of certain antidepressants, including tranylcypromine (TCP), which is used in the treatment of depression. We hypothesized that proliferation zones in the adult goldfish brain can be used to determine the antidepressant effects on cellular proliferation. Here, we report that bromodeoxyuridine (BrdU) labeling over a 24-hr period can be used to rapidly identify the proliferation zones throughout the goldfish brain, including the telencephalon, diencephalon, optic tectal lobes, cerebellum, and facial and vagal lobes. In the first 24 hr of BrdU administration, TCP caused an approximate and significant doubling of labeled cells in the combined brain regions examined, as detected by BrdU immunohistochemistry. TCP caused the greatest increase in cell proliferation in the cerebellum. The normal migratory paths of the proliferating cells within the cerebellum were not affected by TCP treatment. These results indicate that the goldfish provide significant advantages as a vertebrate model for rapidly investigating the effects of antidepressant drugs on cellular proliferation and migration in the normal and injured brain.

Ocean acidification slows retinal function in a damselfish through interference with GABAA receptors

Vision is one of the most efficient senses used by animals to catch prey and avoid predators. Therefore, any deficiency in the visual system could have important consequences for individual performance. We examined the effect of CO2 levels projected to occur by the end of this century on retinal responses in a damselfish, by determining the threshold of its flicker electroretinogram (fERG). The maximal flicker frequency of the retina was reduced by continuous exposure to elevated CO2, potentially impairing the capacity of fish to react to fast events. This effect was rapidly counteracted by treatment with a GABA antagonist (gabazine), indicating that GABAA receptor function is disrupted by elevated CO2. In addition to demonstrating the effects of elevated CO2 on fast flicker fusion of marine fishes, our results show that the fish retina could be a model system to study the effects of high CO2 on neural processing.

A grouped retina provides high temporal resolution in the weakly electric fish Gnathonemus petersii

Weakly electric fish orient, hunt and communicate by emitting electrical pulses, enabling them to discriminate objects, conspecifics and prey. In addition to the electrosensory modality - although dominating in importance in these fishes - other modalities, like vision, play important roles for survival. The visual system of Gnathonemus petersii, a member of the family mormyridae living in West African blackwater streams shows remarkable specializations: Cone photoreceptors are grouped in bundles within a light reflecting tapetum lucidum, while the rods are also bundled but located at the back within a light-scattering guanine layer. Such an organization does not improve light sensitivity nor does it provide high spatial resolution. Thus, the function of the grouped retinal arrangement for the visual performance of the fish remains unclear. Here we investigated the contrast sensitivity of the temporal transfer properties of the visual system of Gnathonemus. To do so, we analyzed visual evoked potentials in the optic tectum and tested the critical flicker fusion frequency in a behavioral paradigm. Results obtained in Gnathonemus are compared to results obtained with goldfish (Carassius auratus), revealing differences in the filter characteristics of their visual systems: While goldfish responds best to low frequencies, Gnathonemus responds best at higher frequencies. The visual system of goldfish shows characteristics of a low-pass filter while the visual system of Gnathonemus has characteristics of a band-pass filter. Furthermore we show that the visual system of Gnathonemus is more robust towards contrast reduction as compared to the goldfish. The grouped retina might enable Gnathonemus to see large, fast moving objects even under low contrast conditions. Due to the fact that the electric sense is a modality of limited range, it is tempting to speculate that the retinal specialization of Gnathonemus petersii might be advantageous for predator avoidance even when brightness differences are small.

General principles in motion vision: color blindness of object motion depends on pattern velocity in honeybee and goldfish

Visual systems can undergo striking adaptations to specific visual environments during evolution, but they can also be very "conservative." This seems to be the case in motion vision, which is surprisingly similar in species as distant as honeybee and goldfish. In both visual systems, motion vision measured with the optomotor response is color blind and mediated by one photoreceptor type only. Here, we ask whether this is also the case if the moving stimulus is restricted to a small part of the visual field, and test what influence velocity may have on chromatic motion perception. Honeybees were trained to discriminate between clockwise- and counterclockwise-rotating sector disks. Six types of disk stimuli differing in green receptor contrast were tested using three different rotational velocities. When green receptor contrast was at a minimum, bees were able to discriminate rotation directions with all colored disks at slow velocities of 6 and 12 Hz contrast frequency but not with a relatively high velocity of 24 Hz. In the goldfish experiment, the animals were trained to detect a moving red or blue disk presented in a green surround. Discrimination ability between this stimulus and a homogenous green background was poor when the M-cone type was not or only slightly modulated considering high stimulus velocity (7 cm/s). However, discrimination was improved with slower stimulus velocities (4 and 2 cm/s). These behavioral results indicate that there is potentially an object motion system in both honeybee and goldfish, which is able to incorporate color information at relatively low velocities but is color blind with higher speed. We thus propose that both honeybees and goldfish have multiple subsystems of object motion, which include achromatic as well as chromatic processing.

Lungfish aestivating activities are locked in distinct encephalic γ-aminobutyric acid type A receptor α subunits

Ammonia in dipnoans plays a crucial role on neuronal homeostasis, especially for those brain areas that maintain torpor and awakening states in equilibrium. In the present study, specific α subunits of the major neuroreceptor inhibitory complex (GABA(A) R), which predominated during some phases of aestivation of the lungfish Protopterus annectens, turned out to be key adaptive factors of this species. From the isolation, for the first time, of the encoding sequence for GABA(A) R α₁, α₄ , and α₅ subunits in Protopterus annectens, qPCR and in situ hybridization levels of α₄ transcript in thalamic (P < 0.001) and mesencephalic (P < 0.01) areas proved to be significantly higher during long aestivating maintenance states. Very evident α₅ mRNA levels were detected in diencephalon during short inductive aestivating states, whereas an α₄ /α₁ turnover characterized the arousal state. Contextually, the recovery of physiological activities appeared to be tightly related to an evident up-regulation of α₁ transcripts in telencephalic and cerebellar sites. Surprisingly, TUNEL and amino cupric silver methods corroborated apoptotic and neurodegenerative cellular events, respectively, above all in telencephalon and cerebellum of lungfish exposed to long maintenance aestivating conditions. Overall, these results tend to underlie a novel GABAergic-related ON/OFF molecular switch operating during aestivation of the lungfish, which might have a bearing on sleeping disorders.

Systemic thyroid hormone is necessary and sufficient to induce ultraviolet-sensitive cone loss in the juvenile rainbow trout retina

Rainbow trout possess ultraviolet-sensitive (UVS) cones in their retina that degenerate naturally during development. This phenomenon can be induced with exogenous thyroxine [T4, a thyroid hormone (TH)] treatment. However, the previous T4 exposure experiments employed static water immersion; a method that could introduce confounding stress effects on the fish. Because of this, it was uncertain if T4 alone was sufficient to induce retinal changes or if stress-related hormones were also necessary to initiate this process. Furthermore, it was unclear whether endogenous T4 was the factor responsible for initiating natural UVS cone loss during development. The current study examined the role of systemic T4 on the juvenile rainbow trout retina using a slow-release implant. Exogenous T4 treatment resulted in SWS1 opsin downregulation and UVS cone loss after four weeks of exposure, signifying that T4 is sufficient to induce this process. Blocking endogenous T4 production with propylthiouracil (PTU, an anti-thyroid agent) attenuated SWS1 downregulation and UVS cone loss in the retina of naturally developing rainbow trout, suggesting that endogenous T4 is necessary to initiate retinal remodelling during development. Quantitative real-time RT-PCR analysis demonstrated that several TH-regulating components are expressed in the trout retina, and that expression levels of the TH receptor isoform TRbeta and the type 2 deiodinase (D2) change with T4 treatment. This suggests that T4 may act directly on the retina to induce UVS cone loss. Taken together, these results demonstrate that systemic TH is necessary and sufficient to induce SWS1 opsin downregulation and UVS cone loss in the retina of juvenile rainbow trout.