Abstract
Purpose: :
To study the spatio-temporal receptive fields and encoding of luminance information in populations of rabbit retinal ganglion cells (RGCs) which survive after optic nerve section (ONS).
Methods: :
Adult New Zealand rabbits weighing 1000-1500 g were used in this study. All experimental procedures were carried out in accordance with the ARVO and European Communities Council Directives (86/609/ECC) for the use of laboratory animals. The right optic nerve was completely sectioned 4 mm behind the eyeball and the left eye was used as control. RGCs were selectively labeled by injection of dextrometilrodamine (DTMR) into the optic nerve, during surgical procedures. One month after the ONS, extracellular recordings were made from RGCs in the isolated superfused rabbit retina using an array of 100 microelectrodes. Simultaneous single- and multi-unit responses were obtained in response to various spatial, intensity and temporally modulated visual stimuli. Responses were recorded with a 100 channel data acquisition system (Bionic Technologies Inc) and stored on a Pentium-based computer for later analysis.
Results: :
We found a significant decrease in the number of recorded RGCs (<30%) in the axotomized retinas vs. control animals. One month after the ONS, a group of surviving RGCs showed light correlated activity with prominent "OFF" responses. However many axotomized RGCs spilke continuously. In addition, spectral-temporal maps (STM) revealed that 75% of axotomized RGCs showed an increased oscillatory activity in the range of 5-130 Hz. Some of these events are directly correlated with the re-apparition of characteristic features of immaturity.
Conclusions: :
Multielectrode arrays provide a useful means to record simultaneously from many RGCs in axotomized retinas. The RGCs that survive axotomy maintain certain degree of functionality but undergo several physiological changes that maybe related with activity-dependent development of new circuits within the retina.
Keywords: apoptosis/cell death • receptive fields • ganglion cells