The absence of specific dye-coupling among frog spinal neurons

A double fluorescence labeling technique was developed to study the specificity of dye-coupling among frog spinal neurons. A pool of motoneurons known to be electrically coupled was prelabeled with a large molecule (rhodamine conjugated to horseradish peroxidase) that was not expected to pass through gap junctions. Then a single sensory or motor neuron within or outside this pool was injected with lucifer yellow to see if the dye spread specifically among neurons that are electrically coupled. We observed almost no examples of specific dye-coupling.