Type I intrinsically photosensitive retinal ganglion cells of early post-natal development correspond to the M4 subtype

Table 6 Summary of age-dependent ipRGC changes

Parameter	P8 Type I	P8 Type II	P8 Type III	P15/30 Type II	P15/30 Type III
Percent cells with continuous firing during exposure	9 %	0 %	0 %	23 %	16 %
Percent cells with intermittent firing during exposure	10 %	0 %	0 %	23 %	15 %
Recovery values: On-latency (sec)	11	61	12	33	26
Recovery values: Off-latency (sec)	27	11	27	26	7
Percent recovery: Peak Firing	65 %	0 %	55 %	25 %	13 %
Percent recovery: Total Spikes	108 %	0 %	40 %	3 %	27 %
Percent recovery: Initial Spikes	92 %	0 %	65 %	2 %	16 %
Percent recovery: Steady-state Spikes	138 %	1 %	76 %	3 %	33 %
Anatomically corresponding cell	M4	M2	M1	M2	M1
Somatic melanopsin level in anatomically corresponding cell over development	↓	No significant change	No significant change
Dendritic melanopsin level in anatomically correspondent cell over development	↓↓	↓	↓

Summary of changes in light exposure parameters, recovery parameters, and melanopsin expression levels in cell subtypes over development. Percentages are greatest median percent of pre-exposure values recovered over the 1-h recovery. Time measurements are the greatest median times recovered over the 1-h. Post-eye-opening (PEO)

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