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

Abstract

We describe the postnatal development of the electroretinogram (ERG) receptoral response in the guinea pig. In addition, the time course and nature of maturation was compared between albino and pigmented strains to consider the role that melanogenesis might have in this process. Electroretinograms were 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 delayed gaussian model of Hood and Birch [1] fitted as an ensemble to the raw data. Guinea pigs show saturated amplitudes (RmP3) that are 50% of adult values at birth, these mature by PD12. Receptoral delay (t(d)) also undergoes some postnatal maturation, while phototransduction gain (log S) is adult-like at birth. Albino animals had significantly (p<0.05) larger RmP3 and log S across all ages. Guinea pigs have significant postnatal development in their receptoral response. Maturation of RmP3 implies a postnatal increase in rod outer segment length. Whereas the adult values of log S implies a mature phototransduction process at birth. We argue that the likely cause for the larger log S of albino eyes is compatible with theories of increased levels of internal light. Whereas the larger RmP3, even after allowing for increased light effectiveness, may reflect a lower ocular resistance in albino eyes due to their lower levels of melanin. Furthermore, decreased RmP3 and log S with age is observed in the pigmented group only and is consistent with increased ocular resistance due to melanin development in this strain.