Serotonin (5-HT) is an important neurotransmitter involved in depression and other affective disorders (Lucki,1998). The release of 5-HT in neurons is mediated by somatodendritic 5-HT_1A autoreceptors (Ou, 2000). The presence of 5-HT_1A receptor is thought to be increased in depressed patients, producing a reduction in the synthesis of 5-HT (Lemonde,2003).The nuclear DEAF-1 related (NUDR) protein represses the 5-HT_1A promoter region regulating both 5-HT_1A transcription and receptor expression (Lemonde,2003).The SHSY-5Y neuroblastoma cell line is a well characterised system used in neurotransmitter studies. The aim of this study was to determine the presence of 5-HT_1A receptor and NUDR mRNA in this cell line at different time-points by real-time PCR, when differentiated with both nerve growth factor (NGF) and aphidicolin or retinoic acid (RA). The SHSY-5Y cells were grown for different lengths of time (0, 3, 5, 7, 10 and 14 days) in the presence of either RA(10^-5M) or NGF(100ng/ml) and aphidicolin (0.3μM) (LoPresti,1992). RNA was extracted using SV total RNA isolation kit (Promega). cDNA was synthesised using Iscript cDNA synthesis kit (Biorad). For Real-time PCR relative expression ratios were normalised against housekeeping genes ubquitin C (UBC) and trytophan 5-monooxgenase activation protein zeta polypeptide (YHWAZ). Data are presented as means (±SEM). Values represent the relative fold change in 5-HT_1A mRNA compared to undifferentiated cells (time point 0). At day 5 following stimulation with RA a significant 17.2±6.4 fold increase (n=3, p<0.01) in 5-HT_1A receptor mRNA was determined relative to undifferentiated cells (n=3). However, after day 5, 5-HT_1A receptor mRNA levels declined and the change in expression observed was not significantly different relative to undifferentiated cells (7-days 1.5±0.2, 10-days 0.6±0.2, 14-days 4.1±1.5, n=3). Differentiation with NGF and aphidicolin significantly increased 5-HT_1A mRNA levels at 10 days producing an 426±205 fold increase relative to undifferentiated cells (n=6, p<0.01). However, by 14 days of stimulation with NGF and aphidicolin, 5-HT_1A expression had significantly declined to a 4.2±1.8 fold (n=6) change in expression relative to control. A 2.6±1.7 fold increase in NUDR expression was observed at day 5 after treatment with RA (n=3).At day 10 cells differentiated with NGF and aphidicolin a 44.8±27.7 fold increase in NUDR expression was observed (n=6). In conclusion, the results demonstrate that 5-HT_1A receptor and the 5-HT_1A promoter repressor NUDR mRNA are expressed in the SHSY-5Y cell line when differentiated with either NGF and aphidicolin or RA. The differentiated SHSY-5Y cell line may provide a model that will be useful to investigate 5-HT_1A receptor function.