Abnormalities in the synaptic concentration of serotonin are often linked to psychiatric disorders. This concentration of serotonin is regulated, by serotonergic neurons, through a cycle of serotonin synthesis and vesicular packaging, via VMAT, calcium-mediated exocytosis, reuptake via SERT, degradation via MAO, and repackaging in vesicles. Astrocytes are known to contribute to the regulation of synaptic serotonin concentration through the uptake of serotonin and subsequent degradation. This uptake is known to be Na+-dependent and fluoxetine sensitive. This project began by investigating the uptake of serotonin in primary culture astrocytes. Astrocytes are dissociated from 1-3 day old rat pups, cultured for approximately 10 days, and then exposed to 0.3 µM serotonin for 5 hours. Immunofluorescent microscopy results have uncovered localization of serotonin in astrocytes after uptake. This localization may be due to packaging in vesicles via VMAT. We have probed GFAP-positive astrocytes with antibodies for serotonin and VMAT, and found co-localization of both. We are currently verifying the presence of VMAT through amplification of the VMAT transcript by RT-PCR. These results suggest that astrocytes may be capable of packaging serotonin after reuptake. These studies may help uncover novel pharmaceutical targets for the development of treatments for serotonin-related psychiatric disorders.