Morphological study of basic neural circuitry of the lower sacral spinal cord.

2006 Fiscal Year Final Research Report Summary

• Project/Area Number: 16500221
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Nerve anatomy/Neuropathology
• Research Institution: Saga University
• Principal Investigator: SADAHIKO Sadahiko Saga University, Faculty of Medicine, Professor, 医学部, 教授 (20015100)
• Co-Investigator(Kenkyū-buntansha): KAWANO Hitoshi Saga University, Faculty of Medicine, Associate professor, 医学部, 助教授 (10152985) ; MURATA Yuzo Saga University, Faculty of Medicine, Reaserch associate, 医学部, 助手 (20128143) ; LI MIN-ZI Saga University, Faculty of Medicine, Reaserch associate, 医学部, 助手 (00304882)
• Project Period (FY): 2004 – 2006
• Keywords: Spinal cord / Sacral spinal cord / Neural cytoarchitecture / Nerve fibers / Immunohistochemistry / Neurotransmitter / Neuropeptide / Rat

Research Abstract

The most caudal region of the rat spinal cord, the conus medullaris has a simple anatomical feature, which lacks ventral as well as dorsal root fibers and somatic motor neurons in the ventral horn. To analyze this unique structure may provide valuable information on the basic neural cytoarchitecture and fiber connections of the spinal cord, particularly for the intraspinal circuitry. For this purpose, we made light and electron microscopic studies using immunohistochemistry for neuronal markers combined with the transection experiments and/or NADPH-diaphorase histochemistry (a marker for NO synthesizing neuron).
A small number of neurons are distributed around the central canal. These neurons are of small in size (about 10 μm), and some of them are nitric oxide synthase (NOS) positive. A dense distribution of nerve fibers immunoreactive to CGRP, SP, ENK and NPY was found in dorsal part of the conus medullaris similarly to that of other spinal cord levels. In addition, 5-HT-and TH-immuno reactive varicose fibers were richly distributed throughout the sectional plane. After bilateral transection of the dorsal roots (L6-Co3), SP-, ENK-, 5-HT-and TH-immunoreactive fibers showed no significant change, while CGRP-immunoreactive fibers disappeared. These immunoreactive nerve fibers were also unaffected by transverse section of the spinal cord at upper level (L6). Thus, SP-ENK-, 5-HT-and TH-immunoreactive fibers are considered to be originated from intrinsic neurons, and CGRP-immunoreactive fibers are derived from the dorsal root ganglia. NADPH-d-positive neurons around the central canal were associated with ENK-, SP-and 5-HT-immunoreactive nerve terminals, and synaptic contacts with ENK and SP terminals at their dendrites were demonstrated. These results suggest that NOS neurons play an important role in the basic intrinsic neural circuitry of the spinal cord.
The filum terminale (FT) of the rat spinal cord continues caudally from the apex of the conus medullaris at the caudal border of the fourth lumbar vertebra to the fourth segment of the coccyx. It is approximately 6.5 cm in length, and is composed of an internal segment (rostral 2/3, enclosed by the meninges within the sacral canal) and an external segment (caudal 1/3, closely invested by the dura within the narrow vertebral canal of the 1st-4th coccyx). It has been generally described that the external segment of FT is a strand of fibrous tissue. However, the present histological analysis revealed that the central canal of the spinal cord continues down into the full length of the rat FT. The external segment of FT consists of the central canal lined by layer of ciliated ependymal cells with a few neuronal components, and at initial and middle part of the external segment, the central canal abruptly bulges out forming a large sack showing peculiar structures of ependymal cell layer.