Abstract
Purpose :
Lampreys are one of two surviving cyclostome taxa belonging to the superclass Agnatha, or jawless vertebrates. The Agnatha superclass split from the gnathostomes, or jawed vertebrates, about 500 million years ago, making the lamprey an ideal animal model to study evolutionary development of the retina. In this work, we seek to characterize the organization, morphology, and response properties of lamprey retinal interneurons.
Methods :
Whole-cell patch-clamp recordings were made from interneurons in retinal slices of juvenile lamprey (Petromyzon marinus). Patch pipettes contained Alexa-750 dye so that cells could be imaged after recording in order to correlate cell morphology with light responses, and to examine the organization of the inner retina.
Results :
We recorded from several classes of bipolar cells with distinct response profiles, including cells with depolarizing ON responses and cells with hyperpolarizing OFF responses. Many of the bipolar cells had biphasic responses indicating the presence of antagonistic surrounds. Images of filled cells revealed the presence of a Landolt club in several classes of bipolar cells. Recordings were also made from L-type horizontal cells and spiking retinal ganglion cells in the inner nuclear layer (INL).
Conclusions :
Similar to other vertebrates, the inner retina of the lamprey contains both ON and OFF bipolar cells with depolarizing and hyperpolarizing responses. From our preliminary data, it is unclear if the axonal arbors of these bipolar cells stratify into ON and OFF sublamina in the inner plexiform layer, a question that we will seek to answer with additional morphological studies. The presence of both ON and OFF bipolar cells also raises the question of whether, as in other vertebrates, these responses are mediated by metabotropic and ionotropic glutamate receptors. To resolve these questions, we plan to perform electrophysiology studies using synaptic blockers, such as DL-AP4 and CNQX. Further characterization of interneurons of the lamprey retina will help provide insight into the evolutionary development of the retina.
This is a 2020 ARVO Annual Meeting abstract.