Effects of aging on lens transmittance and retinal input to the suprachiasmatic nucleus in golden hamsters

Old animals are less sensitive by almost an order of magnitude to the phase -shifting effects of a low intensity light pulse on the locomotor activity rhythm and the associated induction of immediate early genes in the circadi an clock. The transmittance of energy from 200 to 700 nm through the excise d lens of the eyes of young and old golden hamsters was measured to determi ne if an age-related difference exists in the transmittance of light. There is only a small decrease (8-50%) in transmittance, with the magnitude bein g dependent upon wavelength. No significant differences were detected betwe en young and old animals in the retinal innervation of the suprachiasmatic nucleus (SCN). These results support the hypothesis that the observed decre ase in sensitivity to light in the aged circadian system occurs within the SCN itself and/or retino-hypothalamic tract photoreceptors. (C) 1998 Publis hed by Elsevier Science ireland Ltd. All rights reserved.