Pial surface CSF-contacting texture, subpial and funicular plexus in the thoracic spinal cord in monkey: NADPH diaphorase histological configuration

In spinal cord, white matter is distinguished from grey matter in that it contains ascending and descending axonal tracts. While grey matter gets concentrated with neuronal cell bodies. Notable cell bodies and sensory modality of cerebral spinal fluid (CSF) in white matter are still elusive in certain segment of the spinal cord. Monkey Spinal cord was examined by NADPH diaphorase (NADPH-d) histochemistry. We found that NADPH-d positive neurons clustered and featured flat plane in mediolateral funiculus in caudal thoracic and rostral lumber spinal cord, especially evident in the horizontal sections. Majority of NADPH-d funicular neurons were relatively large size and moderately-or lightly-stained neurons. In horizontal section, the multipolar processes of the neurons were thicker than that of regular other neurons. The processes oriented laterally or obliquely in the lateral funiculus. Some of neuronal cell bodies and proximal processes attached NADPH-d positive buttons or puncta. The neuronal processes interlaced network medially linked to lateral horn (intermediolateral nucleus, IML) and laterally to subpial region, in which formed subpial plexus with subpial NADPH-d neurons. Subpial plexus appeared to contacting externally with CSF. The subpial plexus patterned like round brackets located in lateromarginal pial surface. Compared with sympathetic IML in rostral thoracic segments and sacral parasympathetic IML, the funicular plexus configurated a specialized neuro-texture in caudal thoracic segments. The dendritic arbor of funicular neuron featured variety geometric plane shapes. The funicular plexus oriented exclusive layered flat-plane organization between lateral horn and subpial region in caudal thoracic and rostral lumber spinal cord. The subpial plexus may work as CSF sensor outside of spinal cord. The cluster of funicular neurons may function as locomotion sensor, besides visceral regulation. Different to periventricular CSF contacting or pericentral canal structures, NADPH-d funicular neurons and subpial plexus that located in the pial surface. With advantage of NADPH-d, we found funicular neurons which termed academically as funicular plexus and specialized localization for subpial structure we termed subpial plexus. The funicular texture was regarded as neuronal bridge between the interior CSF in the central canal and external CSF out of the pial surface.