Selective abolition of OFF responses in kainic acid-lesioned chicken retina.
When ganglion cell responses were recorded from optic axons in the superficial layers of the chicken optic tectum, the responses recorded are predominantly ON-OFF transient, with some ON transient, and rare OFF transient responses. Several weeks after excitotoxic lesion of the retina with 40 nmol of kainic acid injected intravitreally, only ON transient responses could be recorded from the contralateral optic tectum. ON response latency and threshold were not affected. At low light intensities responses in the kainic acid-lesioned retinas showed a sustained component which was not detected in control retinas, but at high light intensities, the sustained component disappeared and the responses were extremely transient. The disappearance of the OFF responses seems to be due to elimination of the OFF component of the responses of cells which are normally ON-OFF transient, rather than the silencing of these cells, leaving only the normally ON transient cells. Morphological evidence suggests that approximately two thirds of the bipolar cells and most amacrine cells are destroyed by the kainic acid lesion (Ingham and Morgan, Neuroscience, 9 (1983) 165-181), and pharmacological logic (Morgan, Prog. Retinal Res., 2 (1983) 247-266) suggests that the missing bipolar cells should be OFF bipolar cells. These results therefore suggest that ON-OFF transient cells receive direct input from bipolar cells, which determines their basic response type. These results also suggest that amacrine cells have little if any role to play in the generation of the basic centre responses of these ON-OFF transient ganglion cells, and that while amacrine cells may have a role in the generation of transient responses in the inner plexiform layer, transient responses can be generated without the intervention of amacrine cells, particularly at high intensities.