ATPase activity in the developing chick spinal cord

Characteristics of norepinephrine uptake in developing peripheral nerve terminals

In the chick the various characteristics of [3H]norepinephrine (NE) uptake do not appear simultaneously during the development of the iris. Na+-dependence and ouabain sensitivity are both first seen at a significant level at 10 days of incubation (d.i.). Na+-dependence achieves its peak value at 14 d.i. and is unchanged at 3 months after hatching (a.h.). Ouabain sensitivity increases after its initial appearance to 14 days a.h. and then slowly declines. Temperature sensitivity develops only at hatching and is modified subsequently. Both desmethylimipramine (DMI) and cocaine inhibition develop at 10 d.i. and follow the same developmental pattern; however, DMI appears to be a more effective inhibitor than cocaine. Metanephrine, an inhibtor of extraneuronal uptake, first inhibits NE uptake to a significant degree at hatching. These changes may be related to changes in membrane structure and metabolic function in the developing neuronal membrane. No evidence of [3H]NE uptake is seen at 7 d.i. After this age the Km values tend to fall into two groups, the first 1.3--1.9 X 10(-5) M, up to one month a.h., the second, 3.5--5.0 X 10(-6) M, after one month a.h. There is a large increase in Vmax from 10 to 14 d.i., a period of rapid growth of sympathetic innervation of the iris. Our study suggests that Na+-dependent uptake is a more reliable and constant index of innervation in development than temperature-dependent uptake. It also indicates that in longitudinal developmental studies it is necessary to determine the characteristrics of the transport process of each stage, as characteristics such as N1+-, drug- and temperature-sensitivity may all have unique developmental profiles.

Age dependent changes in choline uptake of the chick iris

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.

Influence of age and short-term starvation on the ATPase activity in the developing rat brain

Na+-K+-stimulated and Mg++-dependent ATPase activities were investigated in the developing cerebral cortex, subcortical structures, and medulla oblongata of rats as was the effect of 24-hr lasting starvation and thirst on those enzyme activities. We found (a) a developmental increase of these ATPase activities in the developing rat brain with the maximum in the cerebral cortex and with the minimum in the medulla oblongata; (b) a decrease of the ratio of these enzyme activities, which was near unity in adult animals; (c) an increase of ATPase activities in the cerebral cortex and subcortical formations of young rats under starvation conditions followed by a decrease of the Mg++/Na+-K+-ATPase activity ratios in these structures; and (d) a decrease of these activities, especially in the cerebral cortex, and an increase of the activity ratios in adult animals under starvation conditions.