Neurotrophins are required by a variety of neuronal types for their survival during development and for the maintenance of normal function in mature animals. Within the nervous system, the neurotrophins are synthesized in limited amounts in postsynaptic cells, glia, or neurons. Within neurons, the neurotrophins are transported both retrogradely and anterogradely to neuronal somata or nerve processes, respectively (see, for example, ref. 1). Because of this mobility, distribution of the corresponding mRNA usually does not match that of the protein. Therefore, to understand their precise function, it is essential to localize both the neurotrophin proteins and their corresponding mRNA. Although immunohistochemistry provides only a view at one instant of time of the antigen’s presence at the site of examination, a more dynamic picture can emerge if several time-points are examined after experimental intervention. The movement of the neurotrophins has been studied extensively by the use of nerve ligations, which allows determination not only of the retrograde and/or anterograde movement of the protein, but also can be useful in demonstrating the absence of a neurotrophin in a particular class of nerves (1).