Expression of the low affinity neurotrophin receptor p75 in spinal motoneurons in a transgenic mouse model for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a lethal neurodegenerative disorder involving motoneuron loss in the cortex, brainstem and spinal cord, resulting in progressive paralysis. Aberrant neurotrophin signalling via the low affinity neurotrophin receptor p75 has been suggested to be involved in the motoneuron death by the activation of apoptotic pathways. In order to investigate the involvement of neurotrophin receptor p75 in the amyotrophic lateral sclerosis related motoneuron degeneration process, we have studied the expression of this receptor in the spinal cord of transgenic mice carrying a mutated human Cu, Zn superoxide dismutase gene. Mutations in the superoxide dismutase gene are one of the genetic causes for familiar amyotrophic lateras sclerosis and human superoxide dismutase-1 transgenic mice develop symptoms and pathology similar to those in human amyotrophic lateras sclerosis. Our study shows that in these mice, spinal motoneurons, which normally do not contain the neurotrophin receptor p75 receptor, express this receptor during the progress of the disease. Expression of the neurotrophin receptor p75 receptor coincides with the expression of activating transcription factor 3, a member of the activating transcription factor/cyclic AMP family of stress transcription factors. Only a minority of these spinal motoneurons actually showed co-expression of neurotrophin receptor p75 with caspase-3 activity, suggesting that expression of the neurotrophin receptor p75 receptor is not directly related to the execution phase of the apoptosis process.

Expression of interleukin-1 beta in rat dorsal root ganglia

The expression of interleukin-1beta was examined in dorsal root ganglion (DRG) neurons from adult rats using non-radioactive in situ hybridization and immunocytochemistry. At all spinal levels, approximately 70% of the DRG neurons appeared to express IL-1beta mRNA; about 80% of these DRG neurons actually appeared to produce the IL-1beta protein at markedly varying levels. The expression of IL-1beta was found in large as well as in intermediate diameter sensory neurons but only sporadically in the population of small sensory neurons. The population of IL-1beta immunopositive sensory neurons included most of the large calretinin-positive Ia afferents, but only a few of the small substance P/CGRP positive sensory neurons. In situ hybridization staining for the detection of type 1 IL-1 receptor showed expression of this receptor by most of the sensory neurons as well as by supportive glial-like cells, presumably satellite cells. The functional significance of IL-1beta in the DRG neurons needs to be elucidated, but we speculate that IL-1beta produced by DRG neurons may be an auto/paracrine signalling molecule in sensory transmission.