Neurofilament immunoreactivity in developing rat autonomic and sensory ganglia

Immunoreactivity to neurofilament (NF) antiserum appears early in the development of both the central and peripheral nervous systems of the rat fetus. In 10 somite embryos, positive cell bodies are present in the ventromedial part of anterior rhombencephalic and mesencephalic neural tube. From there the appearance of immunoreactivity spreads cranially to the prosencephalic anlage before closure of the anterior neuropore and caudally following the sequence of neural tube closure. Immunoreactivity increases rapidly in axon bundles of central and peripheral systems, but in immature cell bodies of sensory ganglia the NF material only forms a ring around the nucleus. At 16 days of gestation, some cell bodies are progressively loaded with NF-immunoreactive material as a thick perinuclear network first and then in more excentrically located aggregates. This category of neurons is mainly observed in the distal part of the trigeminal ganglion, in petrous and nodose ganglia and in cervical dorsal root ganglia. In adult ganglia large cell bodies and some small ones present high NF immunoreactivity. In autonomic cell bodies (in superior cervical ganglion and in parasympathetic cranial ganglia) the immunoreactive material only forms a perinuclear ring slowly transformed into a loose perinuciear meshwork at the end of gestation. Intensely reactive nerve fibers are observed in cranial sensory as well as in sympathetic and parasympathetic ganglia and nerves. No positive cell bodies and only a few NF-immunoreactive nerves are observed in the carotid bodies. The NF immunoreactivity is better visualized on sections of fresh frozen material, treated with acetone, than in fixed specimens. These results are compared to previous observations reported for other species and for developing dorsal root ganglia. This immunostaining may be used to detect differentiation of peripheral sensory and autonomic neurons under experimental conditions. The uneven distribution of NF immunoreactivity in sensory neurons from stage 16 days of gestation as specific for precise subpopulations of neurons is discussed.