Morphological and Histochemical Changes in Intercellular Junctional Complexes in Epithelial Cells of Mouse Small Intestine Upon X-Irradiation: Changes of Ruthenium Red Permeability and Calcium Content

Changes of calcium-content and permeability of tight junction following X-irradiation were investigated in mouse intestinal epithelial cells by electron microscopy. In the control animals the lower parts of tight junctional area as well as the other junctional elements and the intercellular space are labeled by pyroantimonate precipitates, which contain calcium as revealed by electron spectroscopy and electron energy loss spectrometry. X-irradiation, parallel with morphological changes, lead to rapid decrease of pyroantimonate precipitable calcium content and increase of the permeability of tight junctions indicated by the penetration of ruthenium red into the intercellular space. These changes were readily reversible following 0,5 Gy doses of irradiation however, they persisted up to 24 hours following 5 Gy irradiation. We conclude that irradiation at the applied doses can transiently destabilize the tight junctions in the epithelial layer of the small intestine, presumably through a calcium dependent mechanism

Talampanel reduces the level of motoneuronal calcium in transgenic mutant SOD1 mice only if applied presymptomatically

We tested the efficacy of treatment with talampanel in a mutant SOD1 mouse model of ALS by measuring intracellular calcium levels and loss of spinal motor neurons. We intended to mimic the clinical study; hence, treatment was started when the clinical symptoms were already present. The data were compared with the results of similar treatment started at a presymptomatic stage. Transgenic and wild-type mice were treated either with talampanel or with vehicle, starting in pre-symptomatic or symptomatic stages. The density of motor neurons was determined by the physical disector, and their intracellular calcium level was assayed electron microscopically. Results showed that motor neurons in the SOD1 mice exhibited an elevated calcium level, which could be reduced, but not restored, with talampanel only when the treatment was started presymptomatically. Treatment in either presymptomatic or symptomatic stages failed to rescue the motor neurons. We conclude that talampanel reduces motoneuronal calcium in a mouse model of ALS, but its efficacy declines as the disease progresses, suggesting that medication initiation in the earlier stages of the disease might be more effective

Elevation of intracellular calcium content in area CA1 of hippocampus is not directly correlated with the development of long-term potentiation.

Electron microscopic localization of calcium-containing mitochondria in stratum radiatum of CA1 of hippocampal slices was performed after (I) low-frequency stimulation, (2) high-frequency stimulation, and (3) blocking Full-size image (<1 K) (NMDA) receptors during high-frequency stimulation. Dendritic mitochondria containing Ca deposits were found in a narrow band of stratum radiatum 280–350 μm distant from stratum pyramidale. Axonal mitochondria containing Ca deposits were evently distributed in stratum radiatum. The total number of calcium containing-mitochondria was highest in long-term potentiated slices, and less in slices treated with APV; the lowest values were obtained with low-frequency stimulation

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