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Microglial movement to sites of nerve lesion in the leech CNS
Abstract:
The small glial cells in the central nervous system of the leech, Hirudo medicinalis, have been studied using two histological stains. Weak silver carbonate, a classic stain for vertebrate microglia, can selectively stain these small glial cells and shows that they are morphologically similar to vertebrate microglia. Feulgen's DNA-specific stain is useful for counting the compact and distinctive microglial nuclei. In uninjured connectives, which link segmental ganglia, there are 134 +/- 28 microglia per 210 micron of connective length. Within 24 h after the nerve cord is crushed leech microglia aggregate at the site of injury. This increase in cells, seen both in vivo and in culture, is approximately 5-fold. Although cells do not continue to accumulate at the injury site after the first day, their numbers continue to vary with time in the regions immediately adjacent to the crush for at least one week. A second crush made 24 h after the first shows that leech microglia are capable of responding to repeated injury.
Insights
Leech microglia, small glial cells in the central nervous system, are morphologically similar to vertebrate microglia and rapidly aggregate at injury sites. These cells show a notable response to nerve cord injury and repeated trauma.
Area of Science:
- Neuroscience
- Cell Biology
- Histology
Background:
- The central nervous system of the leech (Hirudo medicinalis) contains small glial cells.
- These cells have not been extensively characterized in relation to vertebrate microglia.
Purpose of the Study:
- To characterize leech small glial cells using histological stains.
- To investigate the response of these glial cells to nerve cord injury.
Main Methods:
- Histological staining using weak silver carbonate and Feulgen's DNA-specific stain.
- Quantitative analysis of glial cell density in uninjured connectives.
- Observation of glial cell aggregation in vivo and in culture following nerve cord crush injury.
- Assessment of response to repeated injury.
Main Results:
- Weak silver carbonate selectively stained leech glial cells, revealing morphological similarities to vertebrate microglia.
- Feulgen's stain allowed for counting of glial cell nuclei.
- Uninjured connectives contained approximately 134 +/- 28 glial cells per 210 microns.
- Within 24 hours of nerve cord injury, leech glial cells showed a 5-fold aggregation at the injury site.
- Glial cell numbers remained elevated in adjacent regions for at least one week post-injury.
- Leech glial cells demonstrated a capacity to respond to repeated injury.
Conclusions:
- Leech small glial cells share morphological and reactive properties with vertebrate microglia.
- These glial cells exhibit a robust inflammatory-like response to central nervous system injury.
- The study provides a foundation for further investigation into glial cell function in invertebrates.