Confocal microscopy and the Ca(2+)-sensitive fluorescent dye fluo-3 were used to study subcellular Ca2+ signals in embryonic, neonatal, and adult dorsal root ganglion (DRG) neurons in excised dorsal root ganglia. Optical images obtained from isolated whole embryonic and neonatal ganglia revealed a marked variability in the resting Ca2+ signals of different neurons as compared to signals in adult neurons which were uniformly faint. Many of the embryonic and neonatal neurons displayed nuclear Ca2+ signals at rest which were larger than those in the cytoplasm. Embryonic DRG neurons showed a significant increase in nuclear and cytoplasmic fluorescence in response to depolarization with elevated extracellular potassium or electrical stimulation. A single brief electrical stimulus was sufficient to elicit nuclear Ca2+ signals in a subset of the embryonic neurons. The depolarization-induced Ca2+ signals were blocked by removal of extracellular Ca2+, but not by treatment with 2,5-di (tert-butyl)-1,4 benzohydroquinone (DTBHQ), a compound which depletes intracellular Ca2+ stores. The intensity of the depolarization-induced Ca2+ signals declined significantly between the late embryonic (E18-E20) and early postnatal time periods (P0-P1). The nuclear and cytoplasmic Ca2+ signals of the embryonic DRG neurons in the excised tissue preparation occur at a time of intense target innervation, suggesting a role for Ca2+ signals in the development and maturation of rat DRG neurons.