Positron emission tomography: an animal model of spinal distribution of drugs after intrathecal administration.

An animal model has been developed in the Rhesus monkey for noninvasive monitoring of CSF transport of drugs by external detectors i.e. positron emission tomography. The model compromises the cannulation of the subarachnoid space (with a spinal needle), and has been used without any damage to the monkey. With the method it was shown that injection rate had a major influence on the transport rate of 68GaCl3 in the CSF. Injection of 0.5 ml over 60 sec gave the highest radioactivity near the injection site, whereas an injection rate of this volume over 10 sec resulted in high radioactivity more rostrally shortly after injection. This method have been of value for the determination of drug kinetics after spinal administration.

Reissner's fiber and the wall of the central canal in the lumbo-sacral region of the bovine spinal cord. Comparative immunocytochemical and ultrastructural study.

Reissner's fiber (RF) of the subcommissural organ (SCO), the central canal and its bordering structures, and the filum terminale were investigated in the bovine spinal cord by use of transmission electron microscopy, histochemical methods and light-microscopic immunocytochemistry. The primary antisera were raised against the bovine RF, or the SCO proper. Comparative immunocytochemical studies were also performed on the lumbo-sacral region of the rat, rabbit, dog and pig. At all levels of the bovine spinal cord, RF was strongly immunoreactive with both antisera. From cervical to upper sacral levels of the bovine spinal cord there was an increasing number of ependymal cells immunostainable with both antisera. The free surface of the central canal was covered by a layer of immunoreactive material. At sacral levels small subependymal immunoreactive cells were observed. From all these structures sharing the same immunoreactivity, only RF was stained by the paraldehyde-fuchsin and periodic-acid-Schiff methods. At the ultrastructural level, ependymal cells with numerous protrusions extending into the central canal were seen in the lower lumbar segments, whereas cells displaying signs of secretory activity were principally found in the ependyma of the upper sacral levels. A few cerebrospinal fluid-contacting neurons were observed at all levels of the spinal cord; they were immunostained with an anti-tubulin serum. The lumbo-sacral segments of the dog, rat and rabbit, either fixed by vascular perfusion or in the same manner as the bovine material, did not show any immunoreactive structure other than RF. The possibilities that the immunoreactive ependymal cells might play a secretory or an absorptive role, or be the result of post-mortem events, are discussed.

Morphometry of the lumbar vertebrae. An anatomic study in two caucasoid ethnic groups.

A morphometric study of the lumbar vertebrae of 121 skeletons, 63 Italian and 58 Indian, revealed that the mean dimensions of the spinal canal, the lateral recesses, and the vertebral body were significantly greater in the Italian than in the Indian skeletons. The lowest normal limits of the midsagittal diameters of the spinal canal were 12.6 mm in the Italian skeletons and 11.5 mm in the Indian series. The midsagittal diameters of the canal measured, at one or more levels, 10.1-10.8 mm in 5% of the Italian skeletons and 9.0-10.5 mm in 10% of the Indian skeletons. In most vertebrae with midsagittal dimensions of the canal less than 11.5 mm, the width of the recesses was at or below the lower limits of normal. These observations cast doubt on the current view that a midsagittal diameter of the vertebral canal of less than 12.0 mm is pathologic and suggest that the diagnosis of developmental stenosis can not be based only on the dimensions of the spinal canal. Lateral recess stenosis may occur in a normally sized spinal canal but is more likely to occur in developmentally narrow canals.

Comparison of several parameters related to the secretory activity of the subcommissural organ in European green frogs.

In European green frogs the secretory activity of the subcommissural organ (SCO) was investigated and quantified measuring three parameters considered to be closely related to the cellular processes of synthesis and release of secretory material by the cells of the SCO: (1) the amount of stained secretory material in the SCO; (2) the amount of secretory material in the SCO labelled by a radioactive precursor; and (3) the growth rate of the "liquor (cerebrospinalis) fibre" (LF). A significant negative linear correlation appears to exist between the growth rate of the LF, on the one hand, and the amount of stained secretory material as well as the amount of radioactively labelled secretory material, on the other hand. A significant positive linear correlation exists between the amounts of stained material and radioactively labelled secretory material. The occurrence in the SCO of European green frogs of a larger amount of stained and/or of radioactively labelled secretory material is probably an expression of a lower (LF-producing) secretory activity. In the light of these observations the suitability of the three parameters as a measure of the secretory activity of the SCO is discussed.

Circulation of cerebrospinal fluid in the bullfrog, Rana catesbiana.

In order to demonstrate features of the cerebrospinal fluid (CSF) path in the amphibian, 2--6 microliters of either Evans Blue-albumin (EBA) or ferrocyanide were injected into the ventricular system of anesthetized bullfrogs. The animals were sacrificed 1 to 135 minutes after injection by either quick freezing (EBA injections) or fixative perfusion (ferrocyanide injections). The contents of the cranial and vertebral cavities were then examined grossly and histologically for distribution of the tracers. In all animals, the tracers were seen throughout the ventricular cavity and in the subarachnoid space surrounding the caudal hindbrain. The site of communication between these two fluid spaces was the posterior tela of the hindbrain. Within this tela, "pores" were found between groups of pavement-like ependymal cells. In many animals, tracer was also observed in the vertebral subarachnoid and epidural spaces, adjacent to spinal nerve roots. In three EBA-injected animals, this tracer was also seen in the subcardinal lymph spaces. These findings suggest that the subarachnoid space in the bullfrog communicates functionally with the ventricular system by way of specialized "pores" in the posterior tela of the hindbrain. There is also indication of movement of fluid within the subarachnoid space which is predominately caudal in direction, with a primary absorptive path for CSF that consists of a perineural route to the lymphatic system.