Ovulatory function and retinal catecholamine concentrations in female rats with and without inherited retinal...

The timing of the critical period and LH surge during the afternoon of proestrus was unchanged in female rats with degenerated retinal photoreceptors (Hunter and Royal College of Surgeons strains), when compared to female rats with intact retinae (Piebald Virol Glaxo and Wistar strains). Both RCS and Wistar strains responded to constant light (LL) exposure by attaining persistent vaginal cornification at the same rate. In addition, both RCS and Wistar strains regained normal estrous cycles when moved from LL to control lighting (LD). Therefore, an intact retinal photoreceptor layer is not essential for normal ovulatory function. In addition, these results show that the effects of LL on gonadotrophin secretion are mediated through the brain and are not the result of retinal degeneration. Measurements of retinal concentrations of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (Dopac), in Wistar and RCS rats showed that concentrations of both compounds were reduced by LL, and then increased back to control values when animals were moved back into LD. Although the magnitude of the changes in retinal concentrations of DA and Dopac was greater in Wistar than in RCS rats (possibly related to the degeneration which occurs in Wistar but not RCS rats), these results suggest that dopaminergic cells, probably within the amacrine cell population of the retina, respond to different light regimes, perhaps by changes in activity.