Faculty Bibliography

The purpose of this study was to ascertain the sequence of events and the cellular constituents involved in reconstituting the cortical mantle after ventricular shunting. The subjects were severely hydrocephalic adult cats. After insertion of a shunt, the ventricular system rapidly returned to normal size and there was gross reconstitution of the cortical mantle. However, there still remained in the cortical mantle many of the histological changes seen before insertion of the shunt. The effect of hydrocephalus is mainly upon axons in the periventricular white matter. The axons become stretched and finally disrupted, resulting in disintegration of the surrounding myelin. In the absence of axons, remyelination cannot take place. It would seem, therefore, that prompt reversal of hydrocephalus is necessary in order to preserve the anatomical and functional integrity of the brain.

The effects of kaolin-induced hydrocephalus on regional blood-flow and water content of cat brain and spinal cord were measured. The role of the central canal of the spinal cord as an alternative pathway for cerebrospinal fluid in experimental hydrocephalus was also studied by positive contrast ventriculography. In comparison with normal cats, blood-flow in the cerebrum, cerebellum and brain stem of cats with acute hydrocephalus was reduced by more than 20 per cent: in those with chronic hydrocephalus it was reduced by only 12 per cent. There was an absolute increase of 1-5 per cent in water content of the brain in cats with acute hydrocephalus. Water content in the spinal cord was increased by 6 per cent in cats with acute hydrocephalus and by 8 per cent in those with chronic hydrocephalus. When the increased water-content was taken into account, hydrocephalus caused no significant change in blood-flow in the cervical, thoracic or lumbar spinal cord. Contrast material perfused through the ventricles of hydrocephalic cats flowed directly into the enlarged central canal of the spinal cord. Kaolin-induced arachnoiditis completely obstructed communication between the ventricles and the cranial subarachnoid space. The contrast material in the central canal communicated both with the cavities extending into the dorsal columns and with the spinal subarachnoid space. When kaolin was injected directly into the spinal subarachnoid space there was an increase in spinal water-content, without an enlarged central canal. These results suggest that in addition to kaolin-induced arachnoiditis, increased intraluminal pressure is necessary to enlarge the central canal.

A brief sketch of the historic development of the concept of neuronal integration is given. Some of the properties of dendritic spikes in chromatolyzed motoneurons, alligator Purkinje cells, and fish oculomotor neurons are reviewed, as well as the various ways in which the generation of dendritic spikes has altered our basic concept of neuronal integration. The principles of dendritic inhibition are elaborated, both as a 'tonic modulatory action' and as a 'functional amputating system' for dendrites that generate spikes.