The myelinated nerve fibers that innervate the infrared receptor membrane of pit vipers were studied under the electronmicroseope. Along the course of the fiber, toward the nerve terminal, segments of the axon with an increasing concentration of mitochondria were found, and a special region was recognized where an active process of mitochondriogenesis seems to occur. In these regions the axon has varying amounts of mitochondria, is devoid of neuroprotofibrils, and the axoplasmic matrix is dense and contains numerous membranes, some of which can be traced as infoldings of the axolemma.
The images observed have led to postulate tentatively a mechanism of mitochondrial formation, which would start with the infolding of the axolemma, would continue with the curving of two parallel membranes around a denser portion of axoplasmic matrix, the development of inner crests and the final closing of the membrane. In this mechanism both the axon membrane and the axoplasmic matrix would be involved.
The possible electrochemical properties of mitochondrial membranes deriving from an excitable membrane are discussed in relation to the special receptive properties of these nerve fibers.
This paper was supported by a grant of the Office of Scientific Research of the U.S. Air Force given to the Instituto de Anatomía General y Embriología, Facultad de Ciencias Médicas, Universidad de Buenos Aires, Argentina.
Postdoctoral fellow of the Instituto Nacional de Microbiología, Buenos Aires, Argentina.