Voltage-sensitive dye recording using retrogradely transported dye in the chicken spinal cord: staining and signal characteristics.

We describe a novel method for retrogradely labeling specific neuronal populations using voltage-sensitive dyes. Styryl dyes were injected into the ventral roots of the isolated embryonic chick spinal cord. After waiting several hours, the dye labeled motoneurons and autonomic preganglionic neurons. Neuronal cell bodies, dendrites and axons were labeled; we presume that the dye traveled either by retrograde transport or by diffusion within the membrane of the axon to which the dyes were initially applied. Using either a photodiode array or a photomultiplier, fluorescence changes could be recorded from motoneurons following antidromic or synaptic activation. Several characteristics of the fluorescence changes were measured indicating that the signals did indeed reflect changes in the motoneuron membrane potential. The best labeling and optical signals were obtained using the relatively hydrophobic dyes di-8-ANEPPQ and di-12-ANEPEQ. In the great majority of cases these dyes responded with an increase in fluorescence of 1-3% (delta F/F) in response to synaptic or antidromic depolarization of the motoneurons. We anticipate that these techniques should be useful in the mapping of activity patterns and connectivity in neural networks within a defined population of neurons.