Rapid and reproducible methods using fluorogold for labelling a subpopulation of cervical motoneurons: application in...

A murine model of motoneuron disease, the wobbler mouse, is characterized by a selective loss of cervical spinal cord motoneurons. To determine the number of motoneurons that degenerate in mice with ongoing disease, we have developed two rapid and reproducible methods for labelling specific pools of cervical motoneurons using the retrograde tracer fluorogold. The motoneurons can be labelled either by capsule application of the tracer onto the sectioned musculo-cutaneous, median and ulnar nerves or by intramuscular (i.m.) injection of the tracer into the biceps brachii muscle and flexor muscles of the forelimb. In wild-type animals, the largest number of retrogradely labelled motoneurons was found 4 days following capsule application ( approximately equal 1900 motoneurons labelled) and 6 days after i.m. injection ( approximately equal1500 motoneurons labelled). Application of these techniques in 5 week-old wobbler mice showed a 36% loss of motoneurons 4 days following tracer application to the cut nerves and a 16% loss 6 days after i.m. injections as compared to values obtained in age-matched wild-type animals in the same conditions. Our results indicate that these procedures can be applied to any rodent model to analyse quantitatively the loss of specific subpopulations of cervical motoneurons and are valuable tools for evaluating novel therapeutics.