Age dependent changes in choline uptake of the chick iris
Related Experiment Videos
Insights
Aging significantly reduces choline uptake in chick irises, impacting acetylcholine synthesis. This study reveals age-related declines in neuronal terminals, not cell bodies, affecting neurotransmitter function.
Area of Science:
- Neuroscience
- Aging Research
- Biochemistry
Background:
- Choline uptake is crucial for acetylcholine synthesis in cholinergic neurons.
- Understanding age-related changes in neuronal function is vital for neurodegenerative disease research.
Purpose of the Study:
- To investigate the age-dependent kinetics of choline uptake in chick irises from 1 to 7 years.
- To correlate these changes with endogenous acetylcholine and choline levels.
- To assess the impact of aging on the sensitivity of choline uptake to various inhibitors and conditions.
Main Methods:
- Studied choline uptake kinetics in chick irises over a 7-year period.
- Measured endogenous acetylcholine and choline levels.
- Assessed sensitivity to hemicholinium, ouabain, and sodium-dependence.
- Evaluated temperature effects (27°C) on uptake.
Main Results:
- Vmax for choline uptake significantly decreased with age, particularly after 5 years.
- Total acetylcholine and choline levels showed a similar age-related decline.
- Sensitivity to hemicholinium decreased, while inhibition by ouabain increased with age.
- Sodium-dependence decreased, and low-temperature uptake remained unchanged in aged irises.
Conclusions:
- Aging specifically affects the neuronal periphery (terminals) rather than cell bodies in peripheral cholinergic neurons.
- The observed changes in choline uptake kinetics and neurotransmitter levels reflect age-related functional decline in neuronal terminals.
Abstract:
The kinetics of the uptake of choline, the rate-limiting substrate in the in vivo synthesis of acetylcholine, were studied during the period 1--7 years in the iris of the chick. These changes were correlated to the endogenous levels of acetylcholine and choline in the same organ. Vmax values per iris decrease significantly at 5 years and continue to decrease at 7 years, to 64% and 37% of the one year value, respectively. If the variation in Vmax is calculaed per protein the decline is 34% between 1 and 5 years. Km does not change significantly during the period 1--7 years. Total acetylcholine and choline levels follow a similar trend, decreasing progressively from 1 to 7 years. Sensitivity to hemicholinium (5.5 X 10(-5) M) decreases significantly between 5 days of incubation (d.i.) and 5 years. Inhibition by ouabain (10(-4) M) shows an opposite trend, increasing significantly from 20% at 5 d.i. to 52% at 3 months. At 5 years sensitivity to ouabain is the same as at 3 months. Nardependence decreases significantly between 5 d.i. and 5 years but no significant changes are seen between 5 d.i. and 3 months. Uptake at 27 degrees C decreases from 59% of control at 5 d.i. to 45% at 3 months, and is not changed at 5 years. Our observations suggest that the effect of aging on peripheral cholinergic neurons is not generalized, but is specifically directed toward the neuronal periphery (terminals) as opposed to cell bodies.