Development of spectral mechanisms in the ground squirrel retina following lid opening

The retina of the California ground squirrel (Spermophilus beecheyi) contains three classes of photopigments (lambda max = 440, 500, 525 nm). From optic nerve recordings it was previously discovered that the effectiveness of signals from the 440 nm cone increase gradually over the weeks following lid opening. In this experiment several features of the electroretinogram (ERG) were examined to assess developmental changes in signals originating in the outer retina. As judged by threshold sensitivity, suprathreshold responsivity, or adaptability, the contribution of the 525 nm mechanism reaches its adult level two to three weeks after lid opening. The 500 nm mechanism appears to have a similar developmental time course. The development of the 440 nm mechanism was tracked using a chromatic adaptation measure. So indexed, the time required for this mechanism to reach its adult status was much greater than that for the other two mechanisms (70-80 days vs 40-45 days of age). The relatively slow development of effectiveness of the 440 spectral mechanism appears to reflect events occurring in the outer retina.