Fig. 6.  In situ hybridization for nerve growth factor (NGF) mRNA in cortex of adult rat brain. Sections are counterstained with fast red for nuclei. (  A) In situ hybridization (ISH) for NGF mRNA with antisense probe. (  B ) A higher magnification of the rectangular area in  A , showing NGF expression (  blue ) in neuron cytoplasm. (  C ) ISH for NGF mRNA with sense probe. (  D ) A higher magnification of the rectangular area in  C .