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EC number: 231-208-1
CAS number: 7446-70-0
The present study was designed to morphologically evaluate the
neurotoxic effects of Al following its injection into the peripheral
nervous system on spinal motor neurons and on the permeability of the
A total of 32 rabbits was divided into five groups and inoculated with
saline (Group 2), maltol (Group 3), AlCl3 (Group 4), Al-maltol (Group
5), or nothing (Group 1). Each agent was injected into the subepineurial
space of the right sciatic nerve. For examination of the permeability of
the blood brain barrier and blood-nerve barrier, 0.5 ml of saline
containing horseradish peroxidase was injected intravenously via ear
vein two weeks after subperineurial injection in one rabbit each from
Groups 1, 2, and 3 and in two rabbits from Group 5.
After two weeks, the rabbits were killed, the lumbar spinal cord,
sciatic nerves and ganglia were fixed, removed and embedded in paraffin.
For morphometric evaluation, 25 serial sections, 6-um thick, were
obtained from the 5th lumbar spinal cord, and every third section was
stained by HE, KB, and Bodian silver methods, respectively. These
sections were divided into the conventional anterior and posterior areas
with the vertical line passing through the central canal to the line
drawn between the outer edge of the posterior median septum and anterior
median fissure, and the number of spheroids / globules in Bodian stained
tissue sections was counted. The numbers of central/ peripheral
chromatolytic neurons, and of degenerated neurons in the anterior area
and posterior area of 25 sections was counted and recorded using
nucleoli as a marker.
The avidin-biotin immunohistochemical technique for phosphorylated and
non-phosphorylated neurofilament, tau, microtubule-associated protein 2
and ubiquitin was used on spinal cord sections. The following mouse
monoclonal antibodies were used in this study: phosphorylated and
non-phosphorylated high- and intermediate-weight neurofilament proteins,
microtubule-associated protein tau, MAP2 and PHF/ubiquitin.
For electron microscopic examination, tissue specimens from the sciatic
nerve and the 5th lumbar spinal cord were postfixed with 1% osmic
tetroxide, dehydrated and embedded in Epon. Semi-thin sections were
stained with toluidine blue, and ultrathin sections were stained with
uranyl acetate and lead citrate.
Argyrophilic round structures (spheroids/globules), were observed in the
neurophil of the spinal anterior horn in Groups 3, 4 and 5, and, to a
lesser degree, in Groups 1 or 2. However, these changes only reached
statistical significance in Group 5, as compared to Groups 1 and 3.
Neurons in the lumbar anterior horn in Groups 4 and 5 and, to a lesser
degree, in Group 3, showed central and peripheral chromatolytic change.
However, in the case of Group 4, these changes were only statistically
significant in the low-dose group (50 ul AlCl3 solution) as compared to
Group 1 and 2 (50 ul saline), and a dose-response relationship was not
The sciatic nerve at the injected site showed mild to moderate edematous
change in the subepineurial space, but the portion 2 cm proximal to the
injected site showed mild edematous change in the subepineurial space.
There were no differences in the morphological changes, among the AlCl3
/ maltol, maltol, and saline injected rabbit groups, although these
changes were more marked in the groups injected with 500 ul and 200 ul
than in those injected with 100 ul and 50 ul. However, the axons and
myelin sheath were well preserved in both the injected and proximal
portion in every group. HRP reactive product was seen in the axons and
cytoplasm of the Schwann cells in the proximal part of the right sciatic
nerve, as well as epithelial cells and pericytes of the spinal vessels
in Group 5 rabbits, but not in Groups 1, 2, or 3 rabbits. The axons that
contained HRP reactive product showed disarrangement of neurofilaments.
The present study has a number of deficiencies:
- Only very few animals were used.
- Test substance concentrations were not analytically verified.
- The different treatment groups are not comparable (i.e. only one
Al-maltol dose level was tested whereas 4 AlCl3 doses were applied).
Furthermore, the substances were applied in different volumes.
- Comprehensive histopathological data are not provided.
Therefore, the study is disregarded and not used for assessment.
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