Clarification of the peripherally located F-actin network around the primary afferent neurons

The primary afferent neurons are enriched for F-actin in the peripheries, giving rise to ring-like appearances when stained with fluorescence probes for actin. A variety of data, mainly obtained from in vitro experiments, suggested that the satellite cell (SC) envelopes around sensory neurons may be a candidate for the F-actin positive structures. However, immunohistochemical studies on dorsal root ganglia (DRGs) suggested that F-actin was located exclusively within the cortical regions of the sensory neurons. Given this discrepancy, the present study has reexamined the distribution of F-actin in the DRGs at both the fluorescence light and electron microscopic levels. Double staining of F-actin with S-100 beta and neural cell adhesion molecule showed that the fluorescence signals for F-actin around the DRG neurons were restricted to the inner margins of the SC envelope. Subsequent ultrastructural observations, by use of a modified anti-FITC system, demonstrated that the F-actin-positive sites corresponded mostly to the adneuronal SC lamellae, while the cortical cytoskeletons in the neurons seemed to contribute little to the typical F-actin staining. The high concentration of F-actin in the SC envelope has not yet described before, and is thought to assist in understanding the functions of the SCs in the ganglia.