Photodynamic injury of isolated neuron and satellite glial cells: morphological study

Potential application of photodynamic therapy (PDT) for treatment of brain tumors including gliomas is currently studied. However, PDT effect on normal glial cells is unknown. We have studied PDT effect using a simple model system - isolated crayfish mechanoreceptor consisting of receptor neuron and surrounding glial cells. Sulphonated alumophthalocyanine photosens (AlPcS_n) localizes predominately in the glial envelope around the neuron. PDT treatment with 10^-7 M photosens inhibits and then irreversibly abolishes neuron activity for approximately 20 min. Then, in 1.7 h after PDT, the plasma membrane loses integrity and extracellular propidium iodide may enter into the cytosol and stain the nuclear chromatin. Neuron nucleus progressively shrinks but apoptotic nucleus fragmentation is not occurred. Such neuron death has been defined as delayed necrosis. Nuclei of the satellite glial cells also shrink. In 8 h after PDT treatment, some of them become fragmented that is characteristic for apoptosis, whereas others lose the plasma membrane integrity and die through necrosis. However, under PDT treatment glial cells not only die but also proliferate and their number is increased. This gliosis is probably aimed to neuron saving.