Dark Rearing Modifies the Morpho-functional Development of Retinal Neurones

Abstract

Abstract: : Purpose: To verify whether dark rearing alters the normal morpho-functional development of retinal circuitry in mammals. Methods: Pigmented rats (Long Evans) were born and raised in complete darkness, the day of the experiments they were anaesthetised and killed by decapitation. One retina was used for immuno- or retinal ganglion cells (RGCs) staining (with DiI) the other one was dissected free, incubated in oxygenated saline and slices (300-500 micron) were cut by hand using an ophthalmic scalpel. Slices were viewed with Nomarski optics on an Axioskop FS2 microscope and continuously superfused with Krebs Ringer bubbled with 95%O2-5%CO2. All recordings from RGCs were made in the whole cell configuration of the patch clamp technique. Data were sampled at 3KHz, acquired by Axotape (Axon Instr.) and analysed using a program written by Dr. Pierre Vincent. Results:Several modifications have been found in dark reared retinas, among the others RGC dendrites ramify throughout the inner plexiform layer (IPL) lacking the restriction of these processes into ON and OFF sublamina. At functional level, spontaneous activity recorded from control and dark-reared retinas (40 days old) is significantly different (6.03 ± 0.64 Hz n=13 in control vs. 2.09 ± 0.27 Hz n=6 in dark reared; P<0.001). Frequency ranged from 3.62 to 14.3 and from 1.74 to 2.63 in control and dark reared animals respectively. The decrease in mean frequency observed in dark reared rats was not accompanied by a decrease in the mean amplitude of synaptic currents respect to the control. These data support the idea that the frequency decrease has a presynaptic origin. Conclusions: Our data provide evidence of the relevant role of light during retinal development even before the beginning of phototransductive process.

Keywords: retinal development • electrophysiology: non-clinical • retina: proximal(bipolar, amacrine, and gangli