Rhythmic gene expression has been correlated to circadian rhythms observed in physiological processes such as liver metabolism, stomach gastric activity and cardiovascular activity. Blood pressure exhibits circadian rhythmicity, dipping during the evening and increasing during the morning, and is controlled by sympathetic nervous system activity. As sympathetic preganglionic neurons (SPNs) are the final common pathway for central nervous system influence on blood pressure, this project aims to determine if SPN function could be regulated by diurnal expression of genes. The diurnal expression of genes encoding proteins involved in determining neuronal activity was investigated in the spinal cord and from micro-punches that included the IML, obtained at 7:30 AM and 7:30 PM. C57/Bl6 mice (N= 10) were terminally anaesthetised, spinal cords removed and RNA extracted. qPCR revealed mRNA levels of Bmal1 and Per2 varied with time of day in the IML; Bmal1 mRNA (0.16 ± 0.03 relative fluorescent units, rfu) was higher at 7:30 PM while Per2 mRNA (0.10 ± 0.02 rfu) was higher in IML at 7:30 AM. To investigate a broader sample of genes, RNAseq was performed on micropunches obtained as above. Diurnal rhythm of expression was observed in potassium channel subunits (e.g. Potassium voltage-gated channel, Shaw-related subfamily, member 3) and glutamate subunits (e.g. Glutamate receptor, ionotropic, N-methyl D-aspartate-associated protein 1) consistent with increased neuronal activity. Diurnal rhythm of Bmal1 and Per2 protein levels in SPNs were then examined using immunofluorescence. C57/Bl6 mice (N= 5 animals n=15 sections) were terminally anaesthetised at 7:30 AM and 7:30 PM and had their spinal cords removed and sectioned. Bmal1 and Per2 protein levels within the SPN nucleus vary with time of day with Bmal1 levels being higher in the 7:30 AM (103.5 ± 4.3 relative units). Single-cell RNA-seq was conducted on patch electrode-aspirated cells from the IML region. C57/Bl6 mice (N= 12) were terminally anaesthetised and had their spinal cords removed and sectioned, cells (N=26) were aspirated from the sections. RNA was extracted from the cells using a kit. SPNs were identified based on expression of choline acetyltransferase gene. Analyses of RNA-seq data is currently ongoing. This study is the first to attempt to characterize the SPN expression profile and diurnal rhythmicity in these cell types.