Figure 3. Expression of the immediate-early gene Fos within the nucleus of LHRH cell body of a rat sacrificed in the afternoon of proestrus. Dual immunoperoxidase procedure was used to detect on the same brain section both Fos (black nucleus) and LHRH (brown cell) immunoreactive proteins. The black reaction (Fos) was obtained by nickel sulfate intensification. Filled arrowhead, nuclear Fos protein located within the nucleus of LHRH neuron.