Cytosine arabinoside (1-beta-D-arabinofuranosylcytosine, AraC) is a commonly used antimitotic agent that kills proliferating cells by inhibiting DNA synthesis. We report that AraC is toxic to cultured chick embryo spinal cord motoneurons (MTNs) in a concentration-dependent fashion with an EC50 of about 2 microM. Interestingly, this type of MTN death is specific, resembles that occurring upon muscle extract (MEX) trophic deprivation regarding its morphological and temporal characteristics, and has apoptotic features, as judged by observation of nuclear morphology. The death of AraC-treated MTNs can be blocked by 2'-deoxycytidine (dC), a pyrimidine metabolite AraC is structurally related to. Overall, these findings suggest that dC may participate in a pathway, different from inhibition of DNA synthesis, that is necessary for cultured MTNs to respond to the trophic activities present in MEX.