Gap junctional communication in the adult central nervous system plays an important role in the generation of network interactions between areas requiring synchronization of oscillatory activities. In vitro studies have shown evidence of electrotonic coupling through gap junctions between sympathetic preganglionic neurones (spns) in the neonatal and adult rat spinal cord (Logan et al. 1996; Leslie et al. 2000). Electrotonic transmission of membrane oscillations might be an important mechanism for recruitment of neurones and result in the generation of rhythmic sympathetic activity at the population level (Marina et al. 2006). Gap junctions in the adult spinal cord are constituted principally by connexin36 (Cx36) (Rash et al. 2000). However, the distribution of Cx36 in specific neuronal populations of the spinal cord is largely unknown. In this study we aim to identify the presence of Cx36 in spns along the thoraco-lumbar spinal cord of the adult rat. Adult Sprague Dawley male rats (280-300gr, n=6) were deeply anaesthetized with urethane (1.3g/kg, IP) and intracardially perfused with paraformaldehyde. The spinal cords and brainstems were collected, postfixed for 60 min and cryo-protected. Double immunostaining against Cx36 (Bittman et al. 2002) and choline acetyltransferase (ChAT) was performed on horizontal sections (20 µm) taken from spinal segments T1-T3, T6-T8, T10-T11, L1-L2. Positive and negative controls were performed in sections of caudal medulla (inferior olive) and spinal cord (motoneurones) to assay specificity of staining for Cx36 and ChAT, respectively. In all the spinal cords analysed, Cx36 punctate immunostaining was greatest in lower thoracic and lumbar segments and it was distributed in the grey and white matter. Cx36 punctate staining was consistently detected in ChAT-immunoreactive neurones from the intermediolateral cell column (IML) and the central autonomic nucleus (CAN). Cx36 puncta were distributed mainly along dendritic processes and to a lesser extent, in neuronal somata. The presence of Cx36 in spns is consistent with electrical coupling between spns through gap junctions in the adult spinal cord.