The environment experienced by young zebrafish influences both the shape and electrical activity of neurons in the eye, which impacts subsequent behavior, according to a June 23 study from neuroscientists at King's College London.
Researchers studied zebrafish during their first five days of life to determine whether visual features in their surroundings affect retinal cell development. The study, published in Neuron, found that fish raised among horizontal stripes developed neurons with different shapes and responses compared to those raised among vertical stripes. Using a virtual reality behavioral test developed with the University of Konstanz, scientists demonstrated that these structural and functional differences influenced how the fish behaved. Zebrafish typically prefer swimming toward stripes parallel to their body orientation; however, this preference was greatly reduced in fish exposed to horizontal stripes early on but retained by those surrounded by vertical lines.
This research is reported as the first demonstration that different environments can influence overall neuron shape in the eye and that these changes map onto later behavior. The observed changes occurred within the retina—a structure responsible for detecting light and basic visual processing. According to researchers, this adds evidence that the retina pre-processes visual scenes before relaying information to other parts of the brain, and shows for the first time that such pre-processing depends on early visual experiences.
To investigate environmental effects on eye development, scientists placed fish in horizontally or vertically striped settings during their initial five days. Stripes are considered salient features used by animals—including humans—to interpret complex images such as faces. Professor Hindges explained: "People actually use horizontal and vertical features to make sense of more complex images like faces, where the nose is a strong vertical line and the brow is a clear horizontal line." Imaging revealed differently shaped retinal neurons between groups; neural activity sent from eye to brain was also biased toward stripe orientations encountered after birth.
Professor Hindges commented, "This has a striking potential to suggest that the places we grow up influence how we see the world... What wasn't known was that these changes are being at least partially driven by changes in the earliest stage of visual processing: in the retina." Dr. Phoebe Reynolds added, "We wanted to explore how these changes that are happening in the eye can impact the actual behavior of the fish... To do this, we developed a novel behavioral test in virtual reality where the fish can display a preference for lines of certain orientations." Professor Armin Bahl said, "Whether these features would also impact the ability to distinguish stripe patterns during behaviour was completely unclear. We were therefore very surprised that conditions... had a major impact on performance." Genetic manipulation allowed researchers to isolate retinal plasticity's contribution; without it, all fish behaved similarly regardless of environment.
The research received funding from several organizations including Medical Research Council (MRC), Leverhulme Trust, Biotechnology and Biological Sciences Research Council, and Emmy Noether Program.
