脊髄傷害後に認められる痙縮の発現機序とくにγ運動系の働きについて

MECHANISMS OF SPASTICITY FOLLOWING SPINAL HEMISECTION, WITH SPECIAL RE-FERENCE TO GAMMA MOTOR SYSTEM

I．はじめに

　疲縮spasticityとか固縮rigidity症状は，種々の疾患や特定の処置によつて，ヒトや動物にひき起こされることが知られているが，このような場合，いわゆるα運動系とともに，γ運動系（Granit, 1955）の関与がどのようであるかが最近とくに問題視されるようになつた。

　さて今日までに提唱されてきた脊髄傷害後に現われる痙縮の発現機序に関する学説のうち，もつとも合理的とみなされるものをあげると，Stavraky （1961）のいわゆる「除神経過敏」説（denervation supersensitivityまたはsupersensitivity of denervated structure）とMcCouch， Austinら（1958）のいわゆる「側芽」sprouting説とがあげられる。ところが実際にあたつて，そのいずれによるか，またはそのいずれがどの程度関与するかについては，今日いずれの学説も直接それを裏づける実証を欠いているものとみなされている。

In order to analyse the mechanism of spasticity developped following spinal hemisection, experiments were performed on 43 chronic adult cats. Great care was taken to compare various phenomena on the hemisected and control sides of the spinal cord.

(1) Marked augmentation of mono- and polysynaptic reflexes of gastrocnemius, semitendinosus or sural nerve was observed on the spastic side judging from lowering of threshold and shifting to the left to the input-output curves.

(2) The discharge patterns of Group Ia fibers in the spastic gastrocnemius muscle suggested the dec-rease of muscle spindle activity in the hemisected side.

(3) Attempt was made to record mass reflex respon-ses of gamma-motoneurons through selective blocking of alpha motor fibers by means of compressing the ventral root proximal to the recording electrode. There was no appreciable difference in the mass gamma-motoneuron reflex responses between the hemisected and control sides.

Above mentioned experimental results suggest that gamma-motor system does not play a primary role in developping spasticity following spinal hemisection. It is worthy to note, however, that spasticity deve-lopped in this experiment is due to some changes in the spinal cord caudal to the hemisection.