DOPA-decarboxylase activity in sciatic nerves of the rat after constriction

Effect of graded ligature compression on nerve conduction

It has been reported that compression over a 12-mm nerve segment in vitro (rubber cuff) or over a 5-cm nerve segment in vivo (using a blood pressure cuff) produces conduction block in large myelinated A fibers before affecting small unmyelinated C fibers. It was concluded that large fibers are more sensitive to compression than are small C fibers. We found, however, when a nerve in vitro was compressed over a short segment (0.5 to 1 mm) using a ligature technique, conduction in small unmyelinated C fibers is blocked before conduction in large myelinated A fibers. These findings have some clinical implications.

Rapid axoplasmic transport of tyrosine hydroxylase in relation to other cytoplasmic constituents

The transport of norepinephrine and two key enzymes involved in its synthesis, tyrosine hydroxylase (EC 1.14.3a) and dopamine beta-hydroxylase (EC 1.14.2.1), has been studied in relation to other axonal constituents in ligated chicken sciatic nerves. Norepinephrine, tyrosine hydroxylase, and dopamine beta-hydroxylase activity all increased proximal to the constriction over a 20-hr period. The rate of transport of norepinephrine, tyrosine hydroxylase, and dopamine beta-hydroxylase were calculated as 2.6, 1.9, and 3.4 mm/hr, respectively. The only enzyme marker to show a similar rate of accumulation was acetylcholinesterase (EC 3.1.1.7), a putative marker for endoplasmic reticulum. The rapid axoplasmic transport of tyrosine hydroxylase from the cell bodies to the terminals of sympathetic neurons may be adequate to account for the elevated amounts of this enzyme in chronically active axon terminals, without the necessity to invoke peripheral axonal synthesis of the enzyme to explain such elevated amounts.