The pontospinal noradrenergic (NA) neurones are thought to form an important anti-nociceptive control system. These neurones are distributed across three areas, locus coeruleus, A5 and A7. Because of the diffuse distribution of NA somata (especially A5) and their widespread projections it has been difficult to study the pontospinal NA system in isolation. To investigate this role in nociception, we have used 2 adenoviral vectors (AVV), Ad-PRS-EGFP (control) and Ad-PRS-Kir2.1-EGFP (Kir), both containing a synthetic promoter element (Hwang et al., 2001) that is specifically active in catecholaminergic neurones to retrogradely target NA neurones that project to the lumbar dorsal horn (Howorth et al., 2005). By expressing a potassium channel (Kir2.1) we have aimed to inhibit these neurones and examine their role in modulating responses to noxious stimuli. Wistar rats (n=36) had injections of control or Kir AVV (tester blinded) under ketamine (5mg/100g) and medetomidine (30µg/100g i.m.) recovery anaesthesia into the lumbar dorsal horn (L4-5). After 7-14 days, the formalin assay was performed (50μl of 5% formalin into the plantar surface of the hindpaw). Flinches and foot lifts were scored for 1 hour and after a further 2 hours, animals were killed with an overdose of pentobarbital. A subgroup of animals (n=8) also had Hargreaves testing before surgery and again prior to formalin testing. The expression of Kir2.1 and c-Fos was determined using fluorescence immunocytochemistry. All data are reported as mean ± S.E.M. In the formalin assay, a typical biphasic behavioural nociceptive response was observed. However, the animals transfected with Kir, showed an increased number of flinches and foot lifts in phase 1 (113±10, n=11 vs control 85±4, n=17, P0.05). c-Fos staining in the spinal cord, was significantly increased in the deep dorsal horn (468±93, n=8 vs control 236±39, n=7, P0.05). Hargreaves testing showed paw withdrawal latency was significantly decreased in the Kir group (pre 15±2s vs post surgery 11±1s, P<0.05, n=4) but not the control group. We have demonstrated the use of an AVV to selectively inhibit noradrenergic neurones projecting to the dorsal horn. Further we have shown that the inhibition of these neurones results in hyperalgesia and increased spinal c-Fos expression. Thus indicating that this small population of pontospinal neurones (~150) projecting to the lumbar dorsal horn play a prominent role in the descending control of nociception.