[The cerebrospinal fluid contact processes in the central canal of the spinal cord. A scanning and transmission electron microscopic study of the rabbit].

The surface of the central canal of the rabbit spinal cord was investigated with scanning and transmission-electron microscopy. On the ventral wall of the central canal, a long cranio-caudally oriented area carries a row of bulbs (about 630 per millimeter of length). The bulbs are spinal ventricular processes of cerebrospinal fluid contacting nerve cells. Its cytoplasm contains mitochondria, smooth- and rough-surfaced endoplasmic reticulum and vesicles of various size and contents. The bipolar or multipolar nerve cells are situated below the ependymal cells of the central canal. The perikaryon has the general cytological structure of a neuron. Some nerve fibres are shown to be running in the cranio-caudal direction within the central canal. Axons containing synaptic vesicles (diameter 400 A) form synapses on some of the ventricular processes. Two main types of ventricular processes can be observed, they differ in the size and structure of the end bulb, in the shape of its sterocilia, and in the number of mitochondria. Big globular processes are filled with a great number of mitochondria, whereas stereocilia are lacking. On the contrary, small processes with numerous stereocilia extending radially into the cerebrospinal fluid contain a number of mitochondria. A third type takes the mid position between the two main types. The ventricular processes have no "sensory cilia". On the basis of these morphological differences the possible role of mitochondrial movements in the function of the ventricular processes and the question of the identity of the three types of processes are discussed.