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.