Abstract
Purpose :
Correlated spiking activity via electrical coupling has been reported to occur only between neighboring homotypic ganglion cells, in line with the concept of parallel processing in the early visual system. Fast reciprocal spike correlations between ganglion cells are thought to occur due to electrical coupling via gap junctions, either directly, or through joint coupling with an intermediary amacrine cell. Here, however, we present evidence for reciprocal correlated firing and gap junction tracer-spread between heterotypic ganglion cells in the guinea pig retina.
Methods :
We recorded the spike responses of several hundred ganglion cells simultaneously in the isolated retina of pigmented guinea pigs by using a large scale multi-electrode array. Spatial noise stimuli were used to measure the receptive field properties of the recorded cells. The spatio-temporal profiles of the receptive fields and autocorrelation functions were used to classify distinct cell types. The retinas were then removed from the array and labeled with the pan-RGC marker RBPMS and the neurofilament marker SMI-32. The individual positions of labeled cell types were then mapped to the functional mosaic of the corresponding type from MEA recordings. To investigate electrical coupling, cross-correlation functions of recorded spike trains were obtained from pairs of cells of a given cell type combination. Retinas were also labeled with acridine orange and cell bodies were targeted based on their shapes for injections with neurobiotin to reveal the morphology of the cells and to investigate tracer spread into electrically coupled cells.
Results :
Fast reciprocal spike correlations indicative of gap junction coupling were observed between sustained ON alpha ganglion cells and another sustained ON ganglion cell type, which both formed independent receptive field mosaics. Both cell types were also homotypically coupled. Neurobiotin-injections of ON alpha ganglion cells revealed tracer spread into amacrine cells and small RBPMS-positive ganglion cell bodies located close to the cell body positions of the injected ON alpha cells. Large cell bodies of homotypically coupled ON alpha cells were located at the outer perimeter of the dendritic trees.
Conclusions :
The results show that interactions between pathways in the early visual system are more complex than previously appreciated. The functional role of fast spike synchronization in heterotypic cell types remains to be examined.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.