Spinal nerve roots
Springer Online Journal Archives 1860-2000
Abstract The purpose of the present investigation was to find out if a compound injected into the spinal subarachnoid space, after having entered ventral and dorsal nerve roots, can be traced to the epineurial-perineurial sheaths and the endoneurium of peripheral nerves. This would indicate a centrifugal movement of substances from the cerebrospinal fluid along nerves; one route of drainage of cerebrospinal fluid which in the past has been widely discussed. In vivo studies were made using Evans blue-albumin and lanthanum chloride as tracers. Evans blue-albumin is macromolecular in size and emits a red fluorescence after exposure to ultraviolet light. Lanthanum ions are small and easily visible in the electron microscope. The tracers were injected into the cervical subarachnoid space and 15 min to 24 h later sampled from roots, dorsal root ganglia, proximal part of spinal nerves and the median nerves were taken and further processed for detection of tracers. Fluorescence microscopy from samples removed 15 min and 24 h after the injection of Evans blue-albumin showed a red fluorescence of low intensity in the endoneurium of nerve roots, ganglia and proximal spinal nerve. After 24 h also the median nerve elicited some fluorescence. The sheaths around these structures were also fluorescent. Lanthanum was detected between cell layers of the nerve root sheath as well as inside the nerve root parenchyma. In about 50% of the samples from dorsal root ganglia extracellular lanthanum was found in the capsule. The tracer was also found in the epineurium of 50% of the spinal nerves and occasionally in the perineurium. At 15 min, 6 h and 15 h lanthanum was often present in the endoneurium of the spinal nerve sample but always absent in the median nerve. At 24 h electron-dense particles identical to, and suspected to be, lanthanum was rarely seen also in the median nerve. The results show that substances in the cerebrospinal fluid can be transferred to other parts of the peripheral nervous system indicating a centrifugal spread, which may take place in  extracellular spaces of the sheaths covering roots, ganglia and nerve, and  endoneurial spaces in roots, ganglia and nerve after passage across the sheath surrounding spinal nerve roots. If absorption of tracer into the blood occurs following injection into the subarachnoid space, leaky blood vessels in ganglia and epineurium may add tracer molecules to the extra-cellular environment of the peripheral nervous system.
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