Reduced axonal transport of dopamine-beta-hydroxylase activity in dystrophic mice: evidence for abnormality of adrenergic nerve cells

The regulation of the retrograde axonal transport of (125)I-beta nerve growth factor is independent of calcium

Calcium has been shown to play a major role in the regulation of endocytosis and exocytosis of synaptic vesicles and retrograde axonal transport of proteins. The role of calcium in the regulation of neurotrophin retrograde axonal transport is unknown. This study aimed to determine if calcium plays a role in the uptake and retrograde axonal transport of (125)I-beta nerve growth factor ((125)I-betaNGF) within sympathetic neurons innervating the iris by comparing it with (125)I-anti-dopamine beta hydroxylase (anti-DBH). The nonspecific voltage-sensitive calcium channel (VSCC) antagonists, cadmium (200 nmol/eye) and nickel (100 nmol/eye) reduced the amount of (125)I-anti-DBH retrograde axonal transport by 90 and 70%, respectively. In contrast, cadmium (200 nmol/eye) had no effect on (125)I-betaNGF retrograde axonal transport, while nickel (100 nmol/eye) caused a significant increase in the amount transported to the ganglia. The L-type VSCC antagonist nifedipine (10 nmol/eye) and N-type VSCC antagonist omega-conotoxin (1.5 nmol/eye) both had no effect on (125)I-anti-DBH retrograde axonal transport which suggests that these types of calcium channels are not involved in the exocytosis/endocytosis of anti-DBH containing vesicles. Thapsigargin (0.2 nmol/eye), an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPases also significantly inhibited (125)I-anti-DBH transport but had no effect on (125)I-betaNGF retrograde transport. This suggests that (125)I-anti-DBH and (125)I-betaNGF are internalized into different vesicle types and that the endocytosis and retrograde axonal transport of (125)I-betaNGF are not dependent upon calcium.

Axonal transport in mdx mouse sciatic nerve

Anterograde and retrograde flows of acetylcholinesterase (AChE) in sciatic nerves of adult mdx mice were compared with those of normal mice. Specific molecular forms of AChE were resolved by high-performance liquid chromatography such that slow anterograde (G1 + G2), fast anterograde and fast retrograde (G4 and A12) flows could be simultaneously studied. Although we found no difference in the total AChE activity and the molecular forms in non-ligated nerves between mdx and the normal mice, ligated nerves showed significant differences. The total AChE activity accumulated at the proximal segment of ligated nerve was higher in mdx mice than in normal mice after 24 h ligation. The G1 + G2 molecular forms were accumulated more in the proximal segment of mdx than the normal. A12, on the other hand, was more abundant in both segments of mdx mice than the normal. No statistically significant difference in the accumulated amount of G4 molecular form was present between mdx and the normal mice at either proximal or distal segment. These results indicated that axonal flow in sciatic nerve likely plays a role in muscle regeneration, and that the transport machinery in dystrophin-deficient mdx neuron is probably normal.

Decreased G4 (10S) acetylcholinesterase content in motor nerves to fast muscles of dystrophic 129/ReJ mice: lack of a specific compartment of nerve acetylcholinesterase?

Acetylcholinesterase (AChE; EC 3.1.1.7) activity and the distribution of its molecular forms were studied in the nervous system of normal and dystrophic 129/ReJ mice, including the sciatic-tibial nerve trunk and motor nerves to slow- and fast-twitch muscles. In normal mice, motor nerves to the slow-twitch soleus exhibited a low AChE activity together with a low level of G4 (10S form) as compared with nerves of the predominantly fast-twitch plantaris and extensor digitorum longus. In contrast, in dystrophic mice, the AChE activity as well as the G4 content of nerves to the fast-twitch muscles were low, displaying an AChE content similar to that of the nerve of the soleus muscle. In the sciatic-tibial nerve trunk, the AChE activity decreased along the nerve in an exponential mode, at rates that were similar in both conditions. However, in dystrophic mice, the AChE activity was reduced throughout the nerve length by a constant value of approximately 180 nmol/h/mg protein. Further analyses indicated that AChE in this nerve trunk was distributed among two compartments, a decaying and a constant one. The decay involved exclusively the globular forms. The activity of A12 (16S form) remained constant along the nerve and was similar in both normal and dystrophic mice. In addition, according to the equation describing the decay of AChE, the reduction in enzymatic activity observed in the dystrophic mice affected mainly G4 in the constant compartment. Brain, spinal cord, sympathetic ganglia, and serum, which were also examined, showed no remarkable differences between the two conditions in their G4 content. The AChE abnormalities that we found in nervous tissues of 129/ReJ dystrophic mice were confined to the motor system.

Study of neurotrophism in normal/dystrophic parabiotic mice

The trophic influences of nerve and muscle on one another were studied in normal and dystrophic littermates of C57BL/6J dy2J mice parabiosed at 20 to 23 days after birth. Each parabiont had a soleus muscle cross-reinnervated by a tibial nerve of its partner. Ultrastructural abnormalities of muscle and endplate were quantified and compared 6 to 7 months postoperatively. The dystrophic nerve degenerated despite reinnervation to a normal muscle. The normal muscle did not prevent the dystrophic nerve from degenerating, and the dystrophic nerve induced degenerative changes in the reinnervated normal muscle. Normal nerve did not retard the genetically programmed degeneration of the dystrophic muscle. The dystrophic muscle, however, did not appear to cause normal nerve terminals to degenerate. We conclude that both nerve and muscle cells in dystrophic mice express characteristics of muscular dystrophy. Muscle fibers of a few motor units further suffer from abnormal neurotrophic influence because of the degeneration of the motor neurons. Myotrophic influence on nerve was not observed.

Axonal transport of nerve growth factor and serum albumin in the dystrophic mouse

Specific (nerve growth factor, NGF) and non-specific (serum albumin, BSA) uptake followed by retrograde axonal transport was studied in the sciatic nerves of normal (C57BL/6J) and dystrophic (dy2J/dy2J) mice. In the dystrophic mouse there was a significant decrease in the amount of NGF transported to dorsal root ganglia or BSA accumulating at a ligature placed on the sciatic nerve.

Reduced axonal transport of 10S acetylcholinesterase in dystrophic mice

Extracts of extensor digitorum longus muscle, atria, brain, and sciatic nerve from phenotypically normal and dystrophic ReJ/129 mice were subjected to sucrose density gradient ultracentrifugation, and the amounts of acetylcholinesterase (AChE) activity associated with each major enzyme form were determined. Normal muscle showed approximately equivalent amounts of the 4S, 10S, and 16S forms of AChE, while dystrophic muscle was relatively deficient in 10S AChE and relatively oversupplied with 4S AChE. This abnormality was not present in the other tissues examined. However, as measured by the 24-hour accumulation of enzyme activity proximal to a ligature on the sciatic nerve, the axonal transport of 10S AChE was only about one third as great in dystrophic as in normal nerve. This result is consistent with the view that the reduction in the amount of this enzyme form in dystrophic muscle could be related to disturbances in a transport-dependent trophic interaction between nerve and muscle.

Motor innervation of the gastrocnemius muscle of wobbler and dystrophic mice

Innervation of the gastrocnemius muscle of mice from the wobbler, dystrophic and C57/BL colonies has been studied. It was found that phenotypically normal mice from each of the colonies did not differ in their innervation properties, hence suggesting no heterozygote penetrance. However, the end-plate complexity increased with age of normal mice. Functional terminal innervation ratio for both the wobbler and dystrophic gastrocnemius muscle was raised above that of the normal and many dystrophic end-plates also appeared abnormal. A study of mice from the wobbler colony manifesting a late onset hind-limb muscle degeneration (Wr/HLD) has been included and the results suggest a relatively benign form of spinal muscular atrophy.