Journal of Neuroscience, Vol 14, 4972-4986, Copyright © 1994 by Society for Neuroscience
Na(+)-dependent, fluoxetine-sensitive serotonin uptake by astrocytes tissue-printed from rat cerebral cortex
V Dave and HK Kimelberg
Division of Neurosurgery, Albany Medical College, New York 12208.
Previous studies have established that rat primary astrocyte cultures
prepared from several brain regions of 1-4-d-old rats exhibit high-
affinity, Na(+)-dependent and fluoxetine-sensitive serotonin (5-HT) uptake
with a Km for 5-HT of 0.4 microM and a Ki for fluoxetine of 23 nM, which
correspond to the characteristics for this transport for other brain
preparations. However, it is not known whether astrocytes in situ show such
uptake. We addressed this question by performing 3H-5- HT uptake
experiments on cortical astrocytes, within 4 hr of isolating them from 6-
and 21-d-old rats by the tissue-print technique. Quantitative
autoradiography was combined with GFAP and neurofilament (NF)
immunocytochemistry to distinguish astrocytic from neuronal 3H-5- HT
uptake. In composition, the tissue-printed (TP) cells and processes were
60-70% GFAP (+) and 10-15% NF(+). 3H-5-HT uptake (0.3 microM 5-HT, 3.4
microCi/ml) in both tissue-printed GFAP(+) astrocytes and NF(+) structures
was sensitive to 1 microM fluoxetine and was also Na+ dependent. More than
90% of TP astrocytes from 6- and 21-d-old rats and 100% of NF(+) structures
from 21-d-old rats showed positive 3H-5-HT uptake (defined as > or = 31
grains/10(3) microns2). The highest level of uptake (> or = 191
grains/10(3) microns2) was never observed in TP astrocytes but was
exhibited by about half of the NF(+) structures. In other experiments were
found that 3H-5-HT uptake by 6-d-old TP astrocytes was comparable to uptake
by postnatal age-matched primary cultured astrocytes that were grown in
fetal bovine serum (FBS). However, primary cultured astrocytes grown in
horse serum showed lower uptake than that observed with FBS, a finding
similar to previous results in cultures where 3H-5-HT uptake was measured
per milligram of cell protein. These results imply that high-affinity,
Na(+)-dependent and fluoxetine-sensitive 5-HT uptake occurs in rat cortical
astrocytes in situ.