Background light adaptation of the retinal neuronal adaptive system. II. Dynamic effects.

The dynamic effects of continuous exposure to light on the neuronal adaptive system of the retina, as indicated by the oscillatory response (OPs) of the electroretinogram (ERG) were studied in the albino rat. Digitally filtered OPs and the a- and b-waves of the corneal ERG were simultaneously recorded in dark adaptation, during continuous light adaptation to four levels of background light (BGL) changing in steps of two log units from 1.43 x 10(-6) cd/m2, referred to as 'low and high scotopic, low and high mesopic' levels. Exposed to 'high scotopic' BGL the total oscillatory response (SOP) significantly enhanced within the first minute, whereas the amplitudes of the a- and b-waves were unaffected. In 'low mesopic' BGL the SOP increased within the first minute, whereas the a- and b-waves significantly decreased. 'High mesopic' BGL instantaneously and profoundly reduced both the SOP and the slow potentials. The individual OPs changed in amplitudes mainly within the first minute of BGL. In general, the earlier OPs (O1 and O2) reacted more to the two 'scotopic' BGL levels, whereas the later OPs (O3 and 04) were more affected by the relatively brighter two 'mesopic' conditions. In conclusion, the rapid increase of the OPs within the first minute of 'high scotopic' and 'low mesopic' BGL exposure may represent a rudimentary light adaptational effect in the rod-dominated rat retina. These findings also suggest that the neuronal adaptive mechanism of the retina seems to be a robust system, probably attaining preservation of visual abilities in the rat on exposure to light.