457
15 FtIR Imaging of tissues: techniques and methods of Analysis
significantly with ageing of animals with Ad disease [131]. the comprehensive
analysis of IR images recorded for the same animal model has given an insight into
chemical composition of the two types of the Aβ deposit, namely dense-core and
diffuse amyloid plaques [132]. the former is associated with dystrophic neurites
and activated glia cells, while the diffuse plaques are amorphous deposits of
β-amyloid peptide without a core and dystrophic neurites. Dense-core plaques are
mainly found in the cortex and hippocampus of the tgCRNd8 mice and they are
characterized by the increased intensity of the amide I band attributed to the presence of β-sheet proteins [132]. moreover, IR imaging of the periphery of the densecore plaques showed an elevated level of phospholipids. this increase was most
pronounced around the large deposits, suggesting location of this plaque within a
phospholipid envelope [132]. Interestingly, synchrotron/FPA-based IR imaging of
the tgCRNd8 hippocampus has demonstrated the ability of this instrumental system to image single neurons located in the close proximity of the amyloid plaque
[133]. IR images recorded with a high spatial resolution show that phospholipids
permeate the core of the plaque, but β-sheet aggregation of the amyloid peptide
extends into the phospholipid bilayer. In turn, the diffuse plaques identified firstly
by immunostaining do not show distinct spectral features when compared to the
ber value typical for α-helical conformation of proteins and no other bands associated with other biomoleules change their positions or relative intensities. this fact
is associated with unaltered morphology of the diffuse plaques, and consequently
with unchanged chemical composition. this type of plaque appears in both normal
and Ad aged brain, indicating that separate processes are responsible for its formation, whereas the core-dense plaques are typical for the Ad disorder [132]. Interestingly, an animal model of pilocarpine-evoked epilepsy shows spectral features
similar to Alzheimer’s disease [134, 135]. IR imaging of a sector 3 in the Ammon’s
horn (CA3) and dentate gyrus (dg) of the hippocampus revealed the presence of
the amide I band at 1657 and 1631 cm
−1
in the control and diseased tissues, respectively. this shift is accompanied by a significant decrease in the absorbance at
1657 cm
−1
[134]. Protein conformation changes towards β-sheet structures appear
along with an increase in content of saturated phospholipids in the pathological hippocampus, especially in pyramidal cells of CA3 as well as in multiform and molecular layers of the dg. the increased level of saturated lipids likely results from
lipid peroxidation and it is proposed as a possible marker of oxidative stress, a
common biochemical event in many neurodegenerative disorders. the appearance
of protein and phospholipid structural changes together may also be indicative of a
process responsible for seizure activity [135]. In addition, creatine inclusions accompanied the β-sheet protein deposits [134]. Few inclusions were observed in the
healthy brain sections, whereas the number of creatine deposits increased to 100 in
the area of the dg and the multiform hippocampal at the acute phase of status epilepticus. It is worth-mentioning that creatine deposits were also identified by the
FtIR imaging technique in the human spinal cord, brain stem, and motor neuron
cortex of two amyotrophic lateral sclerosis human cases, but no alternation of protein conformation was noted [136].
15 FtIR Imaging of tissues: techniques and methods of Analysis
significantly with ageing of animals with Ad disease [131]. the comprehensive
analysis of IR images recorded for the same animal model has given an insight into
chemical composition of the two types of the Aβ deposit, namely dense-core and
diffuse amyloid plaques [132]. the former is associated with dystrophic neurites
and activated glia cells, while the diffuse plaques are amorphous deposits of
β-amyloid peptide without a core and dystrophic neurites. Dense-core plaques are
mainly found in the cortex and hippocampus of the tgCRNd8 mice and they are
characterized by the increased intensity of the amide I band attributed to the presence of β-sheet proteins [132]. moreover, IR imaging of the periphery of the densecore plaques showed an elevated level of phospholipids. this increase was most
pronounced around the large deposits, suggesting location of this plaque within a
phospholipid envelope [132]. Interestingly, synchrotron/FPA-based IR imaging of
the tgCRNd8 hippocampus has demonstrated the ability of this instrumental system to image single neurons located in the close proximity of the amyloid plaque
[133]. IR images recorded with a high spatial resolution show that phospholipids
permeate the core of the plaque, but β-sheet aggregation of the amyloid peptide
extends into the phospholipid bilayer. In turn, the diffuse plaques identified firstly
by immunostaining do not show distinct spectral features when compared to the
ber value typical for α-helical conformation of proteins and no other bands associated with other biomoleules change their positions or relative intensities. this fact
is associated with unaltered morphology of the diffuse plaques, and consequently
with unchanged chemical composition. this type of plaque appears in both normal
and Ad aged brain, indicating that separate processes are responsible for its formation, whereas the core-dense plaques are typical for the Ad disorder [132]. Interestingly, an animal model of pilocarpine-evoked epilepsy shows spectral features
similar to Alzheimer’s disease [134, 135]. IR imaging of a sector 3 in the Ammon’s
horn (CA3) and dentate gyrus (dg) of the hippocampus revealed the presence of
the amide I band at 1657 and 1631 cm
−1
in the control and diseased tissues, respectively. this shift is accompanied by a significant decrease in the absorbance at
1657 cm
−1
[134]. Protein conformation changes towards β-sheet structures appear
along with an increase in content of saturated phospholipids in the pathological hippocampus, especially in pyramidal cells of CA3 as well as in multiform and molecular layers of the dg. the increased level of saturated lipids likely results from
lipid peroxidation and it is proposed as a possible marker of oxidative stress, a
common biochemical event in many neurodegenerative disorders. the appearance
of protein and phospholipid structural changes together may also be indicative of a
process responsible for seizure activity [135]. In addition, creatine inclusions accompanied the β-sheet protein deposits [134]. Few inclusions were observed in the
healthy brain sections, whereas the number of creatine deposits increased to 100 in
the area of the dg and the multiform hippocampal at the acute phase of status epilepticus. It is worth-mentioning that creatine deposits were also identified by the
FtIR imaging technique in the human spinal cord, brain stem, and motor neuron
cortex of two amyotrophic lateral sclerosis human cases, but no alternation of protein conformation was noted [136].