Morphological changes of nerve by nerve block

2011 Fiscal Year Final Research Report

• Project/Area Number: 21592581
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Surgical dentistry
• Research Institution: Iwate Medical University
• Principal Investigator: JYOU Sigeharu 岩手医科大学, 歯学部, 教授 (20154411)
• Project Period (FY): 2009 – 2011
• Keywords: ペインクリニック / 神経ブロック

Research Abstract

A high dose local anesthetic, 5% lidocaine, and a semi-permanent neurolytic agent, 99% alcohol, were infused into the infraorbital foramen, and the morphological change progression from nerve injury to regeneration was observed. And the normal intraneural vascularisation of the infraorbital nerve from the infraorbital foramen to the peripheral vibrissae were examined.
Immediately post drug infusion, there were no significant changes seen in either the alcohol or the lidocaine groups. One day post drug infusion, both the alcohol group and lidocaine group showed near complete destruction of the myelinated nerve fibers within the fascicle. In the alcohol group, this destructed state continued for one month post-procedure, but in the lidocaine group, by the third day post-procedure, the number of destructed myelinated nerve fibers decreased by 50%. In the alcohol group, from 2 months post-procedure to 3 months post-procedure, 75% of the myelinated nerve fibers were less than 5μm in length, while 20% were thick myelinated nerve fibers greater than 5μm. By 6 months post-procedure, thick myelinated nerve fibers were 70%, while thin nerve fibers were 30%, which are close to values found in the control group. In the lidocaine group, from one week post-procedure to 6 months post-procedure, the percentage of myelinated nerve fibers less than 5μm gradually decreased over time, while the percentage of fibers greater than 5μm increased. Approximately 5% remained destructed. Optical microscopic observation of the cross-section of normal mouse infraorbital nerve near the infraorbital foramen revealed nerve fiber fascicles(about 150μm in diameter) covered with epineurium extending from proximal to peripheral areas, increasing in number as they branched. In the nerve fascicle surrounded by the perineurium near the infraorbital foramen, a few blood vessels were distributed. As the nerve fascicle branched and extended, the blood vessels also branched, providing one blood vessel in each nerve fascicle. There were multiple blood vessels in between the epineurium and perineurium. The blood vessels in nerve fascicles consisted of thin branches communicating with blood vessels outside of the perineurium. Nerve fascicles were surrounded by networks of blood vessels communicating with capillaries, arteriolae and venulae. Some blood vessels showed chain-like distribution in nerve fascicles. In the peripheral part of the infraorbital nerve, the blood vessel in the nerve fascicle exited before the nerve entered a vibrissa. There were no blood vessels in the nerve fascicle at the nerve terminal.