Intra-axonal calcium changes after axotomy in wild-type and slow Wallerian degeneration axons

Calcium accumulation induces the breakdown of cytoskeleton and axonal fragmentation in the late stages of Wallerian degeneration. In the early stages there is no evidence for any long-lasting, extensive increase in intra-axonal calcium but there does appear to be some redistribution. We hypothesized that changes in calcium distribution could have an early regulatory role in axonal degeneration in addition to the late executionary role of calcium. Schmidt-Lanterman clefts (SLCs), which allow exchange of metabolites and ions between the periaxonal and extracellular space, are likely to have an increased role when axon segments are separated from the cell body, so we used the oxalate-pyroantimonate method to study calcium at SLCs in distal stumps of transected wild-type and slow Wallerian degeneration (Wld(S)) mutant sciatic nerves, in which Wallerian degeneration is greatly delayed. In wild-type nerves most SLCs show a step gradient of calcium distribution, which is lost at around 20% of SLCs within 3mm of the lesion site by 4-24h after nerve transection. To investigate further the association with Wallerian degeneration, we studied nerves from Wld(S) rats. The step gradient of calcium distribution in Wld(S) is absent in around 20% of the intact nerves beneath SLCs but 4-24h following injury, calcium distribution in transected axons remained similar to that in uninjured nerves. We then used calcium indicators to study influx and buffering of calcium in injured neurites in primary culture. Calcium penetration and the early calcium increase in this system were indistinguishable between Wld(S) and wild-type axons. However, a significant difference was observed during the following hours, when calcium increased in wild-type neurites but not in Wld(S) neurites. We conclude that there is little relationship between calcium distribution and the early stages of Wallerian degeneration at the time points studied in vivo or in vitro but that Wld(S) neurites fail to show a later calcium rise that could be a cause or consequence of the later stages of Wallerian degeneration.

Quantitative assessment of relative changes of immunohistochemical staining by light microscopy in specified anatomical regions

Despite the advent of ever newer microscopic techniques for the study of the distribution of macromolecules in biological tissues, the enzyme-based immunohistochemical (IHC) methods are still used widely and routinely. However, the acquisition of reliable conclusions from the pattern of the reaction products of IHC procedures is hindered by the regular need for subjective judgments, in view of frequent inconsistencies in staining intensity from section to section or in repeated experiments. Consequently, when numerical comparisons are required, light microscopic morphological descriptions are commonly supplemented with analytical data (e.g. from Western blot analyses); however, these cannot be directly associated with accurate structural information and can easily be contaminated with data from outside the region of interest. Alternatively, to eliminate the more or less subjective evaluation of the results of IHC staining, procedures should be developed that correct for the variability of staining through the use of objective criteria. This paper describes a simple procedure, based on digital image analysis methods and the use of an internal reference area on the analyzed sections, that reduces the operator input and hence subjectivity, and makes the relative changes in IHC staining intensity in different experiments comparable. The reference area is situated at a position of the section that is not affected by the experimental treatment, or a disease condition, and that can therefore be used to specify the baseline of the IHC staining. Another source of staining variability is the internal heterogeneity of the object to be characterized, which means that identical fields can never be analyzed. To compensate for this variability, details are given of a systematic random sampling paradigm, which provides simple numerical data describing the extent and strength of IHC staining throughout the entire volume to be characterized. In this integrated approach, the figures are derived by pooling relative IHC staining intensities from all sections of the series from a particular animal. The procedure (1) eliminates the problem arising from the personal assessment of the significance of the IHC staining intensity, (2) does not depend on the precise dissection of the tissue on a gross scale and (3) considerably reduces the consequences of limited, arbitrary sampling of the region of interest for IHC analysis. The quantification procedure is illustrated by data from an experiment in which inflammatory reactions in the murine spinal cord, measured as microglial activation, were followed by IHC after the lesion of the sciatic nerve.