The postnatal development of the oscillatory potentials of the electroretinogram. IV. Mesopic characteristics.

The postnatal development of the oscillatory potentials (OP) of the rat's electroretinogram (ERG) was studied during relatively mesopic adaptational conditions. The behaviour of the OPs induced at an interstimulus interval (ISI) of 30 sec entailed photopic qualities at an individual level, but when summated conformed to a scotopic course of postnatal maturation. An ISI of 1 min elicited OPs with individual scotopic characteristics. The total oscillatory activity culminated at 17 days of age at both ISIs, similar to more scotopically induced oscillations. These results show that relatively mesopic states of adaptation do not promote any earlier appearance of the OPs, and that the immature mesopically induced OPs seem to contain both scotopic and photopic qualities reflecting a postnatal change of balance between these components. Furthermore, photopic mechanisms seem to govern the oscillatory activity in the mature rat retina. We suggest that the differences in relation to adaptational conditions between the immature and mature OPs may reflect the postnatal status of the dopamine and its synthetizing enzyme, tyrosine-hydroxylase.     

The postnatal development of the oscillatory potentials of the electroretinogram. III. Scotopic characteristics.

The postnatal development of the oscillatory potentials (OPs) of the rat electroretinogram (ERG) was studied during more extreme scotopic conditions. Enhancement of scotopic conditions did not facilitate any earlier appearance of the OPs, including the later ones, compared to previously studied less scotopic conditions. The oscillatory activity appeared at Days 12 to 15, and increased rapidly up to Day 17, which coincided with the major period of development of the photoreceptors. After the physiological opening of the eyelids there was a decline of the OPs. We propose that the decline of the oscillatory activity induced during more extreme scotopic conditions is related to early cell death in the distal retina and/or to developmental neuronal plasticity in the proximal retina.