GLIAL UPTAKE OF MONOAMINES IN PRIMARY CULTURES OF RAT MEDIAN RAPHE NUCLEUS AND CEREBELLUM - A COMBINED MONOAMINE FLUORESCENCE AND GLIAL FIBRILLARY ACIDIC PROTEIN IMMUNOFLUORESCENCE STUDY

Glial uptake of serotonin [5-hydroxytryptamine] and dopamine was studied in primary cultures of the median raphe nucleus and cerebellum by using consecutive demonstration of monoamine fluorescence and glial fibrillary acidic protein immunofluorescence. Most of the glial cells taking up monoamines were glial fibrillary acidic protein positive. Astrocytes with a strong immunoreactivity exhibited monoamine fluorescence only occasionally, although such cells did take up L-dopa readily. Glial fibrillary acidic protein negative cells, morphologically identified as astrocytes, exhibited monoamine fluorescence after exposure. Glial uptake of serotonin at a concentration of 10-4 M was detected in cerebellar cultures but not in cultures from the median raphe nucleus. When the concentration was 10-3 M, uptake of serotonin took place in both the areas but was weaker in cultures from the median raphe nucleus. At concentrations > 10-5 M, glial uptake of dopamine was detected in cultures from both the regions studied. No region dependent differences in glial uptake of dopamine were demonstrated. Based on these observations astrocytes and astrocyte-like glial cells take up dopamine and serotonin. Glial cells with markedly high content of the glia fibrillary acidic protein are more resistant to monoamine uptake than cells exhibiting less intense or no glial fibrillary acidic protein immunofluorescence. The existence of regional differences in uptake of serotonin between the median raphe nucleus and cerebellum suggests that glial uptake of monoamines is not an entirely passive mechanism but may be actively controlled by glial cells in a region dependent manner.