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Osmotically induced macrophage activity in the endolymphatic sac. On the possible interaction between periaqueductal
1Department of Otorhinolaryngology and Head and Neck Surgery, University Hospital, Uppsala, Sweden.
Abstract:
This study aimed to investigate the origin of the free cells in the lumen of the endolymphatic sac (ES). Activation of the cells was accomplished through osmotic induction using glycerol. The ES and the perisaccular tissue were analyzed with special reference to the activity of periaqueductal bone marrow cells after different time intervals following the injection of hyperosmotic agents. The results show that the perisaccular or periaqueductal bone marrow space may constitute a source of some of the free cells occurring in the ES. Osmotic challenging of the inner ear may cause activation of the periaqueductal bone marrow, initiating the locomotion and migration of cells (mostly monocytes, neutrophils and eosinophilic leukocytes) along bone marrow sinusoids that frequently anastomose with the ES vessels. The free cells show signs of transepithelial diapedesis and, in the lumen of the ES, cells may develop into phagocytes which initiate the ingestion and degradation of secreted macromolecular aggregates. It is thought that osmotic alterations in the inner ear may give rise to local changes in or around the ES, leading to the chemotactic attraction of bone marrow cells. The results verify the existence of a complex sugar/protein aggregate metabolism over the wall of the ES, which is linked to the turnover of free cells. The findings may indicate that ES macrophages are important in the regulation of inner ear fluid homeostasis.
Insights
Bone marrow cells migrate to the endolymphatic sac (ES) after osmotic challenges, potentially regulating inner ear fluid balance. These cells differentiate into macrophages, aiding in the clearance of inner ear debris.
Area of Science:
- Inner ear physiology
- Cell biology
- Immunology
Background:
- The endolymphatic sac (ES) plays a role in inner ear homeostasis.
- The origin of free cells within the ES lumen remains unclear.
Purpose of the Study:
- To investigate the source of free cells found in the endolymphatic sac lumen.
- To understand the cellular response to osmotic challenges in the inner ear.
Main Methods:
- Osmotic induction using glycerol to activate cells.
- Analysis of the ES and perisaccular tissue.
- Examination of periaqueductal bone marrow cell activity post-injection of hyperosmotic agents.
Main Results:
- Periaqueductal bone marrow is identified as a source of free cells in the ES.
- Osmotic stress activates bone marrow cells (monocytes, neutrophils, eosinophils) to migrate towards ES vessels.
- Free cells exhibit transepithelial diapedesis and differentiate into phagocytes within the ES lumen.
Conclusions:
- Osmotic alterations in the inner ear trigger bone marrow cell migration to the ES.
- ES macrophages are involved in degrading macromolecular aggregates and regulating inner ear fluid homeostasis.
- A complex metabolism of sugar/protein aggregates occurs at the ES wall, linked to cell turnover.