DYE SCREENING AND SIGNAL-TO-NOISE RATIO FOR RETROGRADELY TRANSPORTED VOLTAGE-SENSITIVE DYES

Using a novel method for retrogradely labeling specific neuronal popul ations, we tested different styryl dyes in attempt to find dyes whose staining would be specific, rapid, and lead to large activity dependen t signals. The dyes were injected into the ventral roots of the isolat ed chick spinal cord from embryos at days E9-E12. The voltage-sensitiv e dye signals were recorded from synaptically activated motoneurons us ing a 464 element photodiode array. The best labeling and optical sign als were obtained using the relatively hydrophobic dyes di-8-ANEPPQ an d di-12-ANEPEQ. Over the 24 h period we examined, these dyes bound spe cifically to the cells with axons in the ventral roots. The dyes respo nded with an increase in fluorescence of 1-3% (Delta F/F) in response to synaptic depolarization of the motoneurons. The signal-to-noise rat io obtained in a single trial from a detector that received light from a 14 X 14 mu m(2) area of the motoneuron population was about 10:1. N onetheless, signals on neighboring diodes were similar, suggesting tha t we were not detecting the activity of individual neurons. Retrograde labeling and optical recording with voltage-sensitive dyes provides a means for monitoring the activity of identified neurons in situations where microelectrode recordings are not feasible.