Satellite glial cells (SGCs) have been well known to be present in the sensory and autonomic ganglia of the peripheral nerves and play an important role in various brain functions. However, interactions between the ganglion cells and SGCs involved in transcytosis of materials remained as a poorly-solved problem. In the present study, the cellular processes and molecular mechanisms of the SGCs were investigated in the nodose ganglion (NG) of the rat vagus nerve. Immunofluorescent experiments of the SGCs led to expression of GFAP- and Iba-1-immunoreactivity in close vicinity to neuronal cell bodies. However, very weak Iba-1 expression was seen in GFAP- immunoreactive cells. It was of particular interest that Iba-1- immunoreactive cells seem to be extending a part of the glial cell bodies into neuronal cell bodies in the NG. In electron microscopic experiments, injection of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into the vagus nerve resulted in deep extension of the fine processes of the SGCs into neuronal cell bodies and uptake of HRPreaction product. These findings would indicate that the SGCs respond to environmental changes of neuronal cell bodies are reactive microglial cells in the NG.