Morphologic effects of ammonia on primary astrocyte cultures. II. Electron microscopic studies.

Light microscopic studies of primary astrocyte cultures following exposure to ammonia have shown several alterations. To determine the nature and significance of these changes, electron microscopic studies were performed. Ultrastructural changes consisted of proliferation, pleomorphism and swelling of mitochondria, condensation of the mitochondrial matrix, cytoplasmic lucency and vacuolization, disaggregation of polyribosomal clusters, an initial increase followed by degranulation of rough endoplasmic reticulum, proliferation of smooth endoplasmic reticulum, an accumulation of dense bodies and a loss of intermediate glial filaments. The early alterations appeared reactive and perhaps reflected ammonia detoxification. Some changes were degenerative and support the view that ammonia exerts a direct toxic effect on astrocytes. It is postulated that these changes may interfere with critical astroglial functions and thereby play a key role in the neurologic dysfunction seen in hyperammonemia.