Noradrenergic (NA) neurons in the pons that project to the dorsal horn are thought to form an important antinociceptive control system (Milan, 2002). These NA neurones are distributed across three areas A5, A6 and A7, close to vital brainstem centres. Hence it has been difficult to study the role of this descending NA system in isolation. We have used an adenoviral vector (Ad-PRS) containing a synthetic promoter element (Hwang et al. 2001) that is specifically active in catecholaminergic neurones (Lonergan et al. 2005) to retrogradely target NA neurones that project to the lumbar dorsal horn. We used Ad-PRS transfection to express enhanced green fluorescent protein (eGFP) or monomeric red fluorescent protein (mRFP) and thus mapped the anatomical organisation of the NA system. Wistar rats (130-200g) were anaesthetised (ketamine 5mg/100g and medetomidine 30μg/100g i.m.) and 4-6 injections of Ad-PRS (500nl of 10⁸–10¹⁰ plaque forming units/ml) were made into the lumbar dorsal horn (L4-5, 400μm lateral from midline, 500μm deep to dorsal surface). Animals were killed 1 to 14 days later with an overdose of pentobarbital, perfused with 4% formaldehyde in 0.1M phosphate buffer and the brainstem and spinal cord were removed. Fluorescence immunocytochemistry was undertaken for adenovirus hexon protein and dopamine β hydroxylase (DBH). Neuronal counts from day 7 post injection are reported as mean ± S.E.M. Adenoviral hexon staining showed that the viral transfection at the injection site was confined to the dorsal horn. Retrogradely labelled neurones (127 ± 23, n=8) were only seen in the pontine A5, A6 and A7 areas. DBH staining showed that 95% of all retrogradely labelled neurones were noradrenergic. The majority of labelled cells were found in A6 (80%) with the remainder in A5 (15%) and A7 (5%). This retrograde labelling was seen as early as 1 day after lumbar injection. Unilateral spinal injection showed a predominantly ipsi- but also contralateral projection from A6. Indeed 4% of labelled A6 neurones were shown to project bilaterally to the lumbar dorsal horn using combined injections of eGFP and mRFP expressing vectors. We have demonstrated the use of an adenovirus to selectively target noradrenergic neurones projecting to the dorsal horn using the retrograde transport of the viral vectors by axonal terminals. Such adenoviral transfection strategy provides a powerful tool to explore the function of the noradrenergic system in nociceptive processing by the selective expression of genetic constructs.