Age-related Changes In Dynamics Research Articles

Age related changes in accommodative dynamics in humans

Age related changes in the dynamics of accommodation (far to near focus) and disaccommodation (near to far focus) are reported in this study. Dynamic responses to step stimulus demands from 1 D to 6 D, in 1 D steps, were recorded with a PowerRefractor in 66 subjects in the age range 14–45 years. The accommodative and disaccommodative responses were fit with exponential functions to calculate response amplitude, time constant and peak velocity. The latency of accommodation did not change and the latency of disaccommodation increased with age. For accommodation, time constant increased and peak velocity decreased with age. For disaccommodation, no change in time constant or peak velocity was found with age. The form of the peak velocity vs response amplitude relationship (main sequence) of accommodation changed with age. The differences in the dynamics of accommodation and disaccommodation with age are discussed with reference to the age related changes in the eye leading to presbyopia.

Maturation and aging of the axonal cytoskeleton: Biochemical analysis of transported tubulin

Changes in solubility and axonal transport of tubulin during maturation and aging have been investigated using sciatic motor fibers of rats at 4, 7, 14, 30, and 80 weeks of age. One to six weeks after injection of L-[35S]methionine into the spinal cord, labeled cytoskeletal proteins in consecutive segments of the sciatic nerve and the ventral roots were fractionated into soluble and insoluble forms by extraction in 1% Triton at low temperature. In 4-week-old rats, the two forms of tubulin were transported coordinately in a single wave with the average rate of 2 mm/day. At 7 weeks of age, two components in tubulin transport were observed to develop, possibly reflecting the maturation of the axonal cytoskeleton. The slower main component (1.5 mm/day) contained most of the insoluble form together with the neurofilament proteins and the faster component (3 mm/day) was enriched in the soluble form. Though significantly different in composition, the two components correspond to slow component a (SCa) and slow component b (SCb) originally defined in the optic system. A progressive decrease in transport rates of both SCa and SCb was observed with rats at 14, 30, and 80 weeks of age. In addition, there was a large decrease in the proportion of insoluble tubulin during the course of transport in animals older than 30 weeks. This loss of the insoluble form seems to be accounted for partly by the proteolytic degradation of the severely retarded SCa proteins. Changes in axonal transport of tubulin may thus reflect age-related changes in dynamics and turnover of the axonal cytoskeleton.