Facial nerve transection leads to functional and structural reactions in lesioned motor neurones and surrounding glial cells. Data from this study provide evidence that the most rapid reaction described so far consists of an increase in immunoreactivity of connexin-43 (cx-43), the predominant gap junction protein in astrocytes. The ipsilateral facial nucleus is selectively marked as early as 0.75 to 1.5 hours after axotomy, while the unlesioned side as well as the unoperated controls remain faintly stained. Thus, enhanced coupling capacity of astrocytes by gap junctions appears to be a sensitive indicator of modified neuronal-glial interaction in the CNS.