Cardiovascular physiology exhibits a diurnal rhythm e.g. blood pressure dips at night and increases in the morning. Loss of diurnal rhythm of blood pressure is correlated to an increased risk of developing cardiovascular diseases. Blood pressure is to a large part controlled by sympathetic nervous system activity, which exhibits diurnal activity. Since sympathetic preganglionic neurons (SPNs) are the final common pathway the central nervous system influences blood pressure, this project aims to determine if SPN function could be regulated by diurnal expression of genes. In search of a strategy to isolate SPNs from other spinal cells, the Allen Brain Atlas and/or Gensat project were screened for proteins that appeared to be differentially expressed in SPNs. 38 candidates were identified. Immunohistochemistry was performed to test if these were present in SPNs. To label SPNs C57/Bl6 mice (N= 5) were injected with 0.1ml of 1% Fluorogold IP and 2 days later were terminally anaesthetised and perfused with 4% paraformaldehyde. Despite screening 23 potential markers using immunohistochemistry, only 2 have been detected in SPNs – Galectin-3 and nitric oxide synthase (NOS 1), although they are not present in all SPNs as identified with Fluorogold labelling. The diurnal expression of genes encoding proteins involved in determining neuronal activity in the spinal cord and from micro-punches that include the IML, obtained at morning and evening time points, is being investigated using qPCR. C57/Bl6 mice (N= 10) were terminally anaesthetised and had their spinal cords removed. Initial results indicate that mRNA levels of proteins involved in serotonergic (Htr2a), adrenergic (Adra2a), GABAergic (Gabra5) and cholinergic (ChAT) signalling, vary with time of day. Functional effects of such variations will be tested in future electrophysiology experiments.