Subcellular distribution and axonal transport of noradrenaline, dopamine-?-hydroxylase and neuropeptide Y in dog splenic nerve.

The accumulation of noradrenaline, dopamine-?-hydroxylase and neuropeptide Y was determined at different intervals (6, 12, 24 and 48 h) after ligation of the dog splenic nerve. The calculated anterograde transport velocities for dopamine-?-hydroxylase and neuropeptide Y were quite similar, 9.6 and 9.1 mm/h, respectively. A considerably smaller retrograde transport rate was demonstrated for these compounds. The anterograde transport rate of noradrenaline was found to be 5.2 mm/h. Correcting for the stationary fraction of noradrenaline yielded a transport rate of 10.4 mm/h. The ratio of dopamine-?-hydroxylase/neuropeptide Y was comparable for control and proximal segments of splenic nerve. After differential centrifugation and isopycnic sucrose density gradient centrifugation of splenic nerve homogenates, a major peak of neuropeptide Y, coinciding with noradrenaline and dopamine-?-hydroxylase was found in the high density fractions which are known to contain large "dense-cored" vesicles. The similar transport rates for noradrenaline, dopamine-?-hydroxylase and neuropeptide Y and the comparable ratios of dopamine-?-hydroxylase/neuropeptide Y for control and proximal segments of splenic nerve clearly suggest similar mechanisms of transport for these compounds. Furthermore, the co-distribution of noradrenaline, dopamine-?-hydroxylase and neuropeptide Y in high density fractions, after isopycnic density gradient centrifugation, indicates co-storage of these compounds in large "dense-cored" vesicles in dog splenic nerve.