Abstract
Purpose :
Salamanders have been used in visual neuroscience research for many decades. Nevertheless, there are still a lot of unsolved mysteries about their vision system development and regeneration. Axolotls offer an advantageous animal model for studying life-cycle evolution. To reveal the retinal development in distinct age groups, we investigate neural coding and network processing in axolotls at different life stages: larva, juvenile, and adult by monitoring the activity of RGCs in response to visual contrast and more complex spatiotemporal stimuli. A deeper understanding of early visual information processing will help to elucidate how functional circuitry is formed and organized in the vertebrate retina.
Methods :
Flat-mount retinal preparations from dark-adapted Ambystoma mexicanum (axolotls) at different life stages: larva (2-3cm), juvenile (5-8cm), and adult (>15cm) were placed onto a multi-electrode array (MEA) for extracellular recording. Random binary white noise checkerboard presented at 15 Hz was used to study the spatiotemporal properties of RGCs. Spike-triggered averages (STA) were computed to identify the average stimulus preceding a spike under each condition. Receptive fields (RFs) were mapped and analyzed in polarity, size, and kinetics.
Results :
Axolotls at different developmental stages demonstrated that RGC types vary with age. In adults, 74% of ON-OFF, 22.5% OFF, and 3.5% ON cells and OFF component displayed a sustained spiking pattern while the ON component was more transient. The juvenile group presented 95% ON-OFF, 5% OFF, and very few ON units were found. By analyzing STA, the spatial profiles and time-course of the RF centers are compared between different groups. The sizes of RF centers were 130.34±6.46µm for ON center units and 108.80±2.90µm for OFF units in adults. In the same recording area, premature stage retinae show strong spontaneous spiking activity, but less responses to light stimuli than adults. The RGC spontaneous spiking and light responses in three age groups are under investigation.
Conclusions :
By using MEA recording, we analyzed and revealed changes in retinal visual response properties during developmental processes in axolotls. Unraveling cues of RGC encoding provides crucial insights into the interactions between retinal neurons, which would facilitate our understanding of the formation and alternation of synaptic connectivity during development and regeneration.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.