MECHANISM OF INHIBITORY-ACTION OF CAPSAICIN ON PARTICULATE AXOPLASMIC-TRANSPORT IN SENSORY NEURONS IN CULTURE

The inhibitory effect Of capsaicin on axoplasmic transport in cultured dorsal root ganglion cells was analyzed by video-enhanced contrast mi croscopy. Capsaicin inhibited particle transports in a dose-dependent manner, irrespective of the diameter of axons. The effect of capsaicin was reversible at low concentrations. Capsaicin affected both the ant erograde and retrograde transport. Large organelles were more sensitiv e to capsaicin than small ones in the retrograde transport. An experim ent using calcium-sensitive dye, Fura 2, indicated that capsaicin rais ed the intraneuronal free calcium concentration preceding the inhibiti on of the transport. Electron microscopy revealed that microtubules an d neurofilaments are disorganized and disoriented by capsaicin. We rea ched a conclusion that capsaicin inhibits fast axoplasmic transport of both anterograde and retrograde directions in all types of somatosens ory neurons in culture by disorganizing intraaxonal cytoskeletal struc tures, through the elevated intracellular Ca2+ concentration.