Development of receptoral responses in pigmented and albino guinea-pigs (Cavia porcellus)

We describe the postnatal development of the electroretinogram (ERG) recept oral response in the guinea pig. In addition, the time course and nature of maturation was compared between albino and pigmented strains to consider t he role that melanogenesis might have in this process. Electroretinograms w ere collected on groups of albino and pigmented animals from postnatal day (PD) PD1 to PD60. A-wave amplitudes and implicit times were extracted from filtered data (0-75 Hz). Receptoral components were modelled using the dela yed gaussian model of Hood and Birch [1] fitted as an ensemble to the raw d ata. Guinea pigs show saturated amplitudes (Rm(P3)) that are 50% of adult v alues at birth, these mature by PD12. Receptoral delay (t(d)) also undergoe s some postnatal maturation, while phototransduction gain (log S) is adult- like at birth. Albino animals had significantly (p < 0.05) larger Rm(P3) an d log S across all ages. Guinea pigs have significant postnatal development in their receptoral response. Maturation of Rm(P3) implies a postnatal inc rease in rod outer segment length. Whereas the adult values of log S implie s a mature phototransduction process at birth. We argue that the likely cau se for the larger log S of albino eyes is compatible with theories of incre ased levels of internal light. Whereas the larger Rm(P3), even after allowi ng for increased light effectiveness, may reflect a lower ocular resistance in albino eyes due to their lower levels of melanin. Furthermore, decrease d Rm(P3) and log S with age is observed in the pigmented group only and is consistent with increased ocular resistance due to melanin development in t his strain.